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3.7 Inside the Neutrophil

Case home  ·  Start at the beginning  ·  The Reveal

Time To Read

35–53 minutes

Date Last Modified

The Cell & Its Transport · Chapter 7 of 7

1990, age fifteen: “They took my appendix out on Tuesday. The surgeon called it textbook: fever, pain low on the right, white count up.” At the follow-up the pathology was back — “‘Unremarkable,’ he said, like that was good news” — and the explanation was “probably an early appendicitis that settled down or a virus.” Three weeks later: “The pain came back. Same place, same fever, new scar. I didn’t tell anyone.” This chapter goes inside the white cell that count was made of — how a neutrophil leaves the blood, what it carries, how pyrin builds its alarm — and reads the chart’s undated row about every workup that looked for a germ and found none. Chart Clue #3.

The question you will answer

“White count up” is the only lab-like line in five years of her childhood, and the organ it pointed at turned out to be normal. What is a white count made of, where did those cells go that Tuesday, what did they do when they got there — and what does it mean when every search for a germ comes back empty?

Opener · Textbook · about 2¼ minutes

The opener is the same narrated animation you will watch in Scene 1.

Watch it in Scene 1 ↓

Watch the opener first. It sets the question; the chapter answers it.

1

Read the chart

Patient chart · Stina

1990 · age 15 · “Unremarkable” and three weeks later — and every workup, undated (Chart Clue #3)

1986 · 11
Module 2’s scene, one line back: an ER for a belly pain that “starts under my belly button and slides down low on the right”; “they said it wasn’t my appendix, it was a stomach bug.” By Sunday she was fine.

1990 · 15
“The cycle” (her own account; 3.1’s scene): day one of her period, the fever; then the vomiting; then the legs; three or four days, then it lifts. “It’s on my calendar.”

1990 · 15
The chart’s age-15 row: “Fever, stabbing pain low on the right, white count up: textbook appendicitis. The appendix comes out. Pathology reads it as completely normal.” Diary: the surgeon said “fifteen is right on schedule for an appendix.”

1990 · 15 · three weeks later
“Three weeks later, the same pain returns in the same place. She tells no one.” Diary: “Same place, same fever, new scar. I didn’t tell anyone.”

Every workup · undated
“When she’s acutely ill, doctors look for infection – cultures, scans, the works – and find nothing. The episodes are inflammatory, but sterile: no bug to blame.” No culture is recorded in the diary for 1986–1990, and no lab value of any kind.

Told
“Appendectomy; appendix unremarkable.” “probably an early appendicitis that settled down or a virus” (the surgeon, at the follow-up). “An infection we cannot find.”

Chart clues this module: 3 · logged here (Chapter 7) — undated, “Every workup”; the appendix at fifteen is its childhood instance; no culture or lab value is recorded for 1986–1990

Before you go on · your prediction

Fifteen: fever, pain low on the right, white count up — “textbook.” The appendix comes out and pathology calls it normal; three weeks later the same pain is back in the same place. Before you go inside the white cell, what is the best first reading?

Open the one you lean toward. Nothing is recorded and nothing is revealed — you come back to it at the end.

“Probably an early appendicitis that settled down or a virus”

Watch what an early appendicitis would leave in the appendix wall for a pathologist to find, and whether a virus would bring the pain back to one spot, on a calendar, for years.

Real inflammation in the lining, with no germ in it

Watch what this would need: the right cells in the count, signals that call them with no bacterium, attacks that end on their own.

“Appendectomy; appendix unremarkable” — the organ is out, so the problem should be over

Watch which tissue was on the pathologist’s slide, which tissues stayed behind in her belly, and what the pain did three weeks later.

From Stina’s diary

Age 15 · “Unremarkable”

2

The story

Three short movements: the case, the anatomy and physiology, then the tie back to Stina. Each links to the scene where you’ll see it move.

I · Unremarkable

They took her appendix out on a Tuesday in 1990, when she was fifteen. The surgeon called it textbook: fever, pain low on the right, white count up. He told her she was lucky they had caught it in time, and that fifteen is right on schedule for an appendix. It was not the first time the pain had gone there. At eleven, in another emergency room, it had started under her belly button and slid down low on the right, and the doctors had said it wasn’t her appendix, it was a stomach bug — and by Sunday she was fine; her stomach bugs left “like somebody switched off a light.” This time they took it out. At the follow-up the surgeon said the pathology report was back and the appendix was normal. “‘Unremarkable,’ he said, like that was good news.” She asked him the obvious question: then what caused the pain? Sometimes these things are hard to explain, he said. It was probably an early appendicitis that settled down, or a virus, and anyway it was out now, so she would never have to worry about it again. That same year she worked out the pattern on her own — day one of her period, the fever; then the vomiting; then the legs; three or four days of it, then it lifts — and she wrote: “Nobody has ever asked what all the visits have in common. I know what they have in common. It’s on my calendar.” Nobody asked that day, either. Three weeks after the operation the pain came back. “Same place, same fever, new scar.” She didn’t tell anyone.

See it move: Scene 1 · Textbook · Scene 6 · Sterile

II · The foot soldier and its alarm

A white count is a census. Smear a drop of blood, stain it, count a hundred white cells: on an ordinary day 50 to 70 of them are neutrophils — 10–12 µm across, a nucleus pinched into two to five lobes, a cytoplasm full of fine granules. The marrow makes on the order of a hundred billion a day and keeps a reserve many times larger than the number in your blood; an alarm opens that reserve within hours, and young band forms, nuclei still shaped like horseshoes, spill out with the rest. That is what “white count up” usually means. This foot soldier lives six to eight hours in blood and a day or two in tissue, and dies on the job. Leaving the blood is a four-gate course: signals from inflamed tissue make the vessel lining show selectins, and the cell slows and rolls; chemoattractants — IL-8 (CXCL8) displayed on the wall, C5a and leukotriene B4 drifting in from the tissue — switch on its integrins, which grip ICAM-1 and stop it; it squeezes between endothelial cells (diapedesis) and crawls toward the signal’s source (chemotaxis), actin pushing the front while microtubules hold front and back, their hub (the centrosome) behind the nucleus, toward the tail. Its granules are a toolkit: azurophil granules are specialized lysosomes of myeloperoxidase and elastase, specific granules hold lactoferrin, and a membrane enzyme, NADPH oxidase, fires a respiratory burst that myeloperoxidase turns into bleach. In the cytosol sits pyrin — a sensor, not a brake that fails. While a switch protein called RhoA is on, PKN1 and PKN2 tag pyrin with two phosphates and 14-3-3 proteins clamp it. Switch RhoA off and the clamp lets go; pyrin and ASC build one speck — a step that, in ordinary cells, needs intact microtubules; caspase-1 switches on, cuts pro-IL-1β and gasdermin D, and IL-1β leaves through gasdermin pores. “A fire alarm that builds itself only when there’s smoke.”

See it move: Scene 2 · Innate Immunity’s Foot Soldier · Scene 3 · Roll, Stick, Squeeze, Crawl · Scene 4 · The Ring Assembles · Scene 5 · Rails for the Alarm

III · Sterile, and the clue

Here is the reading nobody in that room could make in 1990. The white count was real, the fever was real, and the pain sat exactly where the surgeon’s hands said it did. The abdominal attack of familial Mediterranean fever is an inflamed peritoneum — the lining’s flat mesothelial cells and the tissue under them filling with neutrophils, its sensitive parietal layer making every movement hurt — and it can imitate appendicitis closely enough that many people with FMF have had a normal appendix removed before anyone named their disease. A pathologist can only report on the tissue in the jar. The appendix was normal, so “Unremarkable” was very likely true: the alarm was in the white cells of the lining around it, and a lining does not come out with an organ. Three weeks later the same lining, in the same place, did it again. That is the shape of sterile inflammation — real inflammation with no pathogen in it, arriving and leaving on its own schedule. FMF is the textbook autoinflammatory disease: innate immune cells firing from the inside, with no germ to blame and no autoantibodies (those would make it autoimmune). In the textbook variant, pyrin’s clamp lets go too easily; her own changed copy, and what one copy can do, is the Chart Reveal’s question (Module 4). Chart Clue #3 is logged here as the chart logs it, undated: every workup looked for infection and found nothing. Honesty flags: the diary records no culture and no lab value from these years, and nobody sampled her peritoneum in 1990 — this is a reading of a pattern, not a slide anyone saw. Decades later Stina found the word herself: “I have been sterile my whole life. Sterile fevers, a sterile appendix…”

See it move: Scene 1 · Textbook · Scene 4 · The Ring Assembles · Scene 6 · Sterile

3

Watch · explore · think · check

6 scenes. Each one has a short animation or a slide, something to explore, a true/false spot-check of your thinking, and a quick check. Every scene gives you an evidence card for your board.

How to read the scenes

  • Animation (dark teal) — a short animated explainer, one idea each
  • Slide (dark teal) — a still to study: a micrograph, a diagram or a map
  • Explore (purple) — something to push on while you watch
  • Game (purple) — a quick challenge
  • Think (gold) — reason it out, then spot-check yourself with a few true/false questions; not graded
  • Check (gold) — a quick H5P that scores itself

Scene 1 of 6

Textbook

Fever, pain low on the right, white count up: three true words — and the third one is a census of neutrophils that can’t say where they went, or why.

Animation · in production · 2 min 20 s

Textbook

A wall calendar for 1990 with one Tuesday circled. Three words stamp down across the frame one at a time: FEVER · PAIN LOW ON THE RIGHT · WHITE COUNT UP. The third stamp opens like a door into a stained blood smear, labeled TEXTBOOK SMEAR — NOT STINA’S (canon keeps no values): a hundred white cells counted into a strip of tally boxes, the neutrophil box about half to two-thirds full. A second smear slides in beside it, labeled DURING ACUTE INFLAMMATION — A MODEL: the neutrophil box overflows, and a few young cells with horseshoe-shaped nuclei are tagged BANDS. Cut to a long bone in cross-section: a marrow cavity packed with finished neutrophils, drawn as sleeping firefighters, and a station door that swings open; the cells pour into a vein. Cut to the belly: a right-lower-quadrant locator on a body outline, then a small vessel running along the peritoneum, the lining’s flat mesothelial cells drawn shoulder to shoulder. Neutrophils leave the vessel and gather in the lining, and the lining glows. Last: the appendix lifted out, set in a jar, a typed label reading UNREMARKABLE. The camera pulls back from the jar to the lining it came out of, still glowing. Caption: A white count says something is inflamed. It doesn’t say where, or why.

Prefer the full lecture? Immunity: Barriers, Fever and Inflammation (original video on the site)

Explore · in production

Count the smear

A virtual microscope field of a stained blood smear: pale pink red cells packed as a background, and scattered among them drawn white cells in a consistent style — neutrophils (two to five lobes, fine pink granules), band neutrophils (one unsegmented, horseshoe-shaped nucleus), lymphocytes (a round dark nucleus filling the cell), monocytes (larger, a kidney-shaped nucleus), eosinophils (two lobes, orange granules) and an occasional basophil (dark granules hiding the nucleus). Beside the field, a lab’s differential counter: six labeled keys — N, BAND, L, M, E, BASO — a running total to 100, and a bar for each cell type. Round 1, BETWEEN ATTACKS · A TEXTBOOK SMEAR: the student identifies and counts 100 white cells; a wrong key flashes a one-line reason (“Two lobes and orange granules — that’s an eosinophil”). At 100 the bars sit beside textbook reference bands (OpenStax): neutrophils 50–70%, lymphocytes 20–40%, monocytes 2–8%, eosinophils 1–4%, basophils 0.5–1%, and a total white count of about 5,000–10,000 per µL. Before Round 2 the student predicts what will happen to the lymphocyte bar — and whether the number of lymphocytes in the blood changes (the animation showed only the neutrophils). Round 2, DURING ACUTE INFLAMMATION · A MODEL: the field refills with more white cells per view, most of them neutrophils, and a handful of bands. Counting it reveals the shift — the neutrophil bar climbs well past its band, bands appear (a “left shift”), the lymphocyte share falls even though lymphocytes haven’t left. A banner keeps the honesty rule in view the whole time: canon keeps no white count for Stina at any age — these are textbook and model smears, and “white count up” in her chart has no number. Round 3, WHERE DID THEY COME FROM? A cross-section of marrow shows a storage pool many times larger than the blood’s supply; dragging an alarm card (IL-1β, IL-6, G-CSF) onto it opens the pool, and a timer shows the count rising within hours, not days. A second card shows the marginated cells — about half the neutrophils in a blood vessel are rolling along its wall, uncounted, until adrenaline or inflammation shakes them loose. Round 4, WHERE DID THEY GO? A slider moves the view from a vein in the arm (where the blood was drawn) to a small vessel along the peritoneum: neutrophils leave the second one and gather in the lining. Last card, WHAT THE COUNT CAN’T SAY: two smears side by side, one labeled a bacterial infection and one labeled inflammation with no germ — and they look the same. The student completes the sentence “A white count tells you ______, not ______ or ______” (that something is inflamed; where; why). Keyboard path: Tab to the field, arrow keys move a focus ring from cell to cell, the letter keys (N, B, L, M, E, S) tally the focused cell, Enter advances a round; every tally is read out in a polite live region (“Neutrophil — 41 of 100”). With prefers-reduced-motion the marrow and vessel scenes are stills with numbered labels. A <details> text version gives both smears as tables (cell type · textbook band · model count) and the four rounds’ conclusions. Alt text for the static view: a stained blood smear with scattered white cells — mostly multilobed neutrophils and a few horseshoe-nucleus bands — beside a six-key tally counter.

Think · not graded

“White count up” was the one lab-like line in her chart at fifteen. Name the cell that most likely made it go up, and where that cell came from within a few hours. Then write what the count cannot tell you — about where the cells went, and about whether a germ called them.

The true/false spot-check for this prompt is in production.

Check · Single Choice

At fifteen the surgeon’s “textbook” included “white count up.” In acute inflammation, what is most of that rise usually made of?

This self-scoring check is in production.

Evidence card 1

Add it to your evidence board

“The surgeon called it textbook: fever, pain low on the right, white count up” — and at the follow-up, “the pathology report was back and the appendix was normal.”

Scene 2 of 6

Innate Immunity’s Foot Soldier

Disposable by design: the most numerous white cell, first to arrive, packed with enzymes and bleach — and the cell doing the inflaming.

Narrated slide · in production · 1 min 02 s

Innate Immunity’s Foot Soldier

Two of Amy’s narrated slides. Slide 1, Inside the Neutrophil (“Pyrin, the inflammasome & microtubules — assembled inside one cell”): “Today we walk through the doorway and find someone living inside”; the membranes, organelles and transport of this module as if they were “just architecture — a wall, a factory, a set of pumps”; the tour — meet the cell, locate the regulator, watch the alarm assemble, follow the signal out, and land on where the medicine acts; “If cell biology felt like a parts list before, watch it become a diagnosis.” Slide 2, Innate Immunity’s Foot Soldier (eyebrow THE CELL OF INTEREST; bullets Most common · First responder · Pyrin lives inside it): “If the immune system had an infantry that was disposable,” this is the foot soldier — the most abundant white cell in the blood, almost always first to arrive; it “crawls toward bacteria, swallows them whole… and dies doing it”; “The cell is doing the inflaming.” Case box on the slide: “Nothing about it looks abnormal under the microscope, which is part of why her diagnosis took so long.” Caption lines under the player (each also a timed caption cue at the moment it is spoken): (1) “For three modules” means this module’s three topics — membranes, organelles and transport (cue at about 0:03); the tour line about where the medicine acts is re-recorded to name the medicine used for FMF — nobody prescribes it in Stina’s story until 2026. (2) Pyrin is not the neutrophil’s alone: it is highest in neutrophils and monocytes, and also made in eosinophils and dendritic cells (site slip 76). (3) The numbers: 10–12 µm across, two to five nuclear lobes, 50–70% of white cells, about 6–8 hours in blood and a day or two in tissue. (4) Phagocytes include neutrophils and macrophages; neutrophils kill inside a phagolysosome with granule enzymes and a respiratory burst, not with peroxisomes.

Prefer the full lecture? Immunity: Barriers, Fever and Inflammation (original video on the site)

Explore · in production

Open the drawers

A wooden specimen cabinet labeled ONE NEUTROPHIL, with five drawers and a work tray in front of it. The drawers are labeled AZUROPHIL (PRIMARY) GRANULES · SPECIFIC (SECONDARY) GRANULES · GELATINASE (TERTIARY) GRANULES · SECRETORY VESICLES · and, set slightly apart, A MEMBRANE ENZYME. Step 1, predict: “When a neutrophil is called out of the blood, which drawer opens first?” The student picks one, then presses Call the cell. The drawers open in their real order with a short line for each, and the prediction is scored: SECRETORY VESICLES first (they carry integrins such as Mac-1 and other receptors to the surface — the cell needs grip before it needs weapons, Scene 3) → GELATINASE GRANULES (gelatinase, MMP-9, which cuts the vessel’s basement membrane on the way out) → SPECIFIC GRANULES (lactoferrin, which grabs the iron bacteria need; lysozyme; parts of the NADPH oxidase) → AZUROPHIL GRANULES last (myeloperoxidase, neutrophil elastase, defensins, cathepsin G — a specialized lysosome, acid hydrolases and all; the bridge back to 3.3). A note under the order: the granules were filled while the cell was maturing in the marrow, azurophils first — the cell spends them in reverse. Step 2, the kill tray: a bacterium token is swallowed into a phagosome. The student chooses tools in any order: fuse an azurophil granule (the phagosome becomes a phagolysosome); switch on the membrane enzyme, NADPH oxidase (superoxide → hydrogen peroxide — the respiratory burst, named for the oxygen it burns, not for breathing); add myeloperoxidase, which turns hydrogen peroxide and chloride into hypochlorous acid, bleach; add lactoferrin to starve it of iron. A kill meter fills; the right combination works fastest. A trap tile labeled PEROXISOME sits on the tray: dropping it in returns “Not a weapon — peroxisomes oxidize fatty acids and detoxify, and their catalase breaks hydrogen peroxide down (3.3).” Step 3, the last resort: a NET card — the cell throws out a web of its own chromatin studded with elastase and myeloperoxidase to trap what it can’t swallow. Step 4, the twist: the bacterium token is removed and the call comes anyway — “a lining with no germ in it.” The drawers still open; elastase, oxidants and bleach now land on the lining’s own cells, and a short honesty line says that tissue injury from neutrophils is real but that how much it contributes to an FMF attack’s pain is not settled. Step 5, the lifespan clock: hours in blood, a day or two in tissue, then the cell dies quietly (apoptosis) and a macrophage eats it — the foot soldier is disposable by design. Keyboard path: Tab to each drawer, Enter opens it, a radio group holds the prediction, Space picks up a tool and Enter drops it on the phagosome; each event is announced in a polite live region (“Specific granules open: lactoferrin, lysozyme, oxidase parts”). A <details> text version lists each drawer, its contents, its release order and its job in a table. Alt text for the static view: a five-drawer specimen cabinet labeled One Neutrophil, one drawer open on small labeled granules, with a tray holding a swallowed bacterium in a bubble.

Think · not graded

A neutrophil lives hours in blood and a day or two in tissue, and it dies on the job. Why would a body build its first responder to be so disposable — and what does a cell full of enzymes and bleach cost the tissue around it when it arrives somewhere with nothing to kill?

The true/false spot-check for this prompt is in production.

Check · Single Choice

What is a neutrophil’s normal job?

This self-scoring check is in production.

Evidence card 2

Add it to your evidence board

“He said I was lucky we caught it in time, and that fifteen is right on schedule for an appendix.”

Scene 3 of 6

Roll, Stick, Squeeze, Crawl

Four gates between the blood and the lining — and not one of them needs a germ to open.

Animation · in production · 2 min 20 s

Roll, Stick, Squeeze, Crawl

A small vein running along the peritoneum, drawn in cutaway: red cells streaming down the middle, the vessel’s flat endothelial cells lining the wall, and beyond the wall the lining’s mesothelium. On the far side, inflamed lining cells send up signal envelopes marked IL-1β and TNF; the endothelium answers by putting E- and P-selectin out on its surface, drawn as small hooks. Gate 1, ROLL: neutrophils drift to the edge of the stream (margination) and begin to tumble along the wall, catching and letting go of the selectin hooks with sugar-tipped ligands on their own surface. Gate 2, ACTIVATE: chemoattractant flags — IL-8 (CXCL8) displayed on the wall, C5a and leukotriene B4 drifting in from the tissue — touch receptors on the rolling cell, and a light inside it switches its integrins on; a fourth slot on the flag board, labeled bacterial product (fMLP), stays empty. Gate 3, STICK: integrins (LFA-1, Mac-1) clamp onto ICAM-1 and the cell stops dead. Gate 4, SQUEEZE: the neutrophil flattens, pushes a foot between two endothelial cells and pulls itself through in an hourglass, its gelatinase cutting a path through the basement membrane (diapedesis). Then CRAWL: a front edge of actin ruffles forward, the nucleus trails, and inside the cell the centrosome sits behind the nucleus, its green microtubules reaching back toward the tail — label: actin pushes the front, microtubules hold front and back (chemotaxis). The cells gather in the lining. A colchicine token waits in the corner (labeled the medicine used for FMF — not in Stina’s story), unplayed: what it does to these moves is the explore’s to reveal. Last frame: the four gates in a row, and the empty fMLP slot. Caption: No germ required.

Prefer the full lecture? Immunity: Barriers, Fever and Inflammation (original video on the site)

Explore · in production

Run the gates

A side-on obstacle course built along a vessel wall, read left to right: a stream lane where a neutrophil token rides with the red cells, then four gates mounted on the wall — GATE 1 ROLL, GATE 2 ACTIVATE, GATE 3 STICK, GATE 4 SQUEEZE & CRAWL — and, past the wall, the peritoneal lining as a finish line. Each gate is locked by a two-part key: one piece on the neutrophil, one on the wall or in the tissue. A molecule tray holds twelve tiles: E-selectin · P-selectin · sugar-tipped ligand (sialyl-Lewis X on PSGL-1) · IL-8 (CXCL8) · CXCR1/2 receptor · C5a · leukotriene B4 · fMLP (a bacterial product) · integrin (LFA-1 / Mac-1) · ICAM-1 · PECAM-1 (a junction protein the cell follows between endothelial cells) · and three decoys: albumin · IL-1Ra · colchicine. Before each gate the student predicts which pair opens it. Gate 1 opens for selectin + its sugar-tipped ligand, and the token slows from a stream speed to a tumble (“catch, let go, catch”). Gate 2 opens for a chemoattractant + its receptor — IL-8, C5a or leukotriene B4 all work; fMLP works too, and a note says bacteria make it — and damaged mitochondria release similar formyl peptides, so even this key can come from the body’s own injured cells. Gate 3 opens for integrin + ICAM-1 — but only after Gate 2 has switched the integrin on; trying it first returns “The integrin is still in its off shape — activation comes first.” Gate 4 opens for PECAM-1, and the token squeezes through in an hourglass; then the student steers the crawl with a direction control while a small readout shows the inside of the cell (actin at the front; the microtubule hub behind the nucleus, toward the tail, holding front and back). Decoys bounce with a reason: albumin (“a carrier protein of plasma; it opens nothing”), IL-1Ra (“it blocks IL-1β’s receptor — it calms gates, it doesn’t open them”). Two toggles after the first full run: NO GERM — the fMLP tile is removed from the tray and the student runs the course again; IL-8, C5a and leukotriene B4 still open Gate 2, and the token still arrives: the course never needed a bacterium. COLCHICINE — drop the colchicine tile on the cell: the microtubule hub fades, Gate 3’s grip weakens and the crawl wanders (labeled: by disrupting microtubules, colchicine reduces how well neutrophils stick and crawl — the medicine used for FMF, not prescribed in Stina’s story). A score panel records each prediction against the reveal. Reveal card: roll on selectins, activate on chemokines, stick on integrins, squeeze and crawl on a cytoskeleton — and every key can be cut from the tissue’s own signals. Keyboard path: Tab to a gate, Enter selects it, arrow keys move through the tray, Space places a tile in the gate’s lock; the direction control takes arrow keys; each gate’s state is announced in a polite live region (“Gate 3 open: integrin bound to ICAM-1 — the cell has stopped”). With prefers-reduced-motion the token jumps gate to gate. A <details> text version lists every gate, its key pair, what happens and the two toggles’ results. Alt text for the static view: a vessel wall with four numbered gates, a neutrophil token waiting in the stream, and a tray of labeled molecule tiles below.

Think · not graded

The four gates — roll, activate, stick, squeeze — work the same whether a germ called the neutrophils or not. Which gate needs a signal from the tissue, and which molecules could send that signal with no bacterium present? What does that tell you about reading “neutrophils arrived” as evidence of infection?

The true/false spot-check for this prompt is in production.

Check · Sort the Paragraphs

Put a neutrophil’s trip from the blood into the inflamed lining in order.

This self-scoring check is in production.

Evidence card 3

Add it to your evidence board

Age eleven, four years before the operation: “It starts under my belly button and slides down low on the right” — and “they said it wasn’t my appendix, it was a stomach bug.”

Scene 4 of 6

The Ring Assembles

Pyrin waits in the cytosol with two tags and a clamp on it; switch RhoA off and a whole alarm machine snaps together — the committed step.

Narrated slide · in production · 1 min 29 s

The Ring Assembles

Two of Amy’s narrated slides. Slide 4, The Inflammasome Assembles (eyebrow THE ALARM MACHINE; “Protein by protein”): the inflammasome “isn’t one molecule — it’s a machine that assembles on demand,” subunits snapping “into a wheel-like complex”; “a fire alarm that builds itself only when there’s smoke”; “Pyrin says, we don’t need this right now. So the machinery stays in pieces until pyrin says, okay… Assemble away”; “It’s kind of like a police officer says, I’ve already started writing the ticket. Right? Assembly is the committed step.” Slide 5, IL-1β Is Produced (eyebrow THE ALARM CYTOKINE; “The signal that spreads”): the assembled machine switches on caspase-1, which “cuts a molecule that’s just kind of hanging out” — pro-IL-1β — into its active form; IL-1β is “the chemical shout that travels,” telling the body to mount fever, pain and inflammation of serous linings “when there is no infection. And this is what is called serositis.” Caption lines under the player: (1) The brake is on pyrin, not pyrin on the alarm: pyrin is itself the sensor that builds this inflammasome. While RhoA is active, the kinases PKN1 and PKN2 tag pyrin at two serines (Ser208, Ser242) and 14-3-3 proteins clamp it; when RhoA is switched off (bacterial toxins such as C. difficile’s TcdA and TcdB do it), the tags come off, the clamp lets go, pyrin’s PYD grabs ASC’s PYD, ASC builds one speck per cell, and the speck switches on caspase-1. (2) Pro-IL-1β had to be made first (a priming signal, Module 2.6’s cut); caspase-1 also cuts pro-IL-18 and gasdermin D, whose pieces open pores that let IL-1β out (3.4 Scene 6) — not exocytosis. (3) Potassium leaving a cell trips a different sensor, NLRP3 (3.6), never pyrin. (4) In FMF the textbook variant lets the clamp go too easily; what her own changed copy does is Module 4’s question. Card beside the player, from Amy’s slide-4 note: “The parts are all normal. The subunits are fine; the enzyme is fine. It’s only the threshold for snapping them together that sits too low.”

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Release the brake

A cutaway of a neutrophil’s cytosol, drawn as a workbench with labeled parts. On the left, a wall switch labeled RhoA (ON · OFF). In the middle, pyrin as one purple token with its PYD end marked, wearing two small phosphate tags (Ser208, Ser242) placed by two kinase hands labeled PKN1 and PKN2, and gripped by a pair of 14-3-3 clamps. Pyrin’s five domains are not redrawn — a link says “Module 2.6 mapped them”. On the right, a parts shelf: ASC pieces (a PYD end and a CARD end), pro-caspase-1, pro-IL-1β, pro-IL-18 and gasdermin D; and across the bench, a line of green microtubule rails. A meter at the top reads THRESHOLD, and a second at the bottom reads IL-1β OUT. Step 1, predict: “Which single change frees pyrin?” — choices: switch RhoA off · add potassium leaving the cell · add a bacterium to the bench · add more pyrin. The student commits, then tries. Only RhoA OFF works: a toxin card (C. difficile toxins TcdA/TcdB, which modify RhoA) flips the switch, the PKN hands stop, the tags fall off one at a time, the 14-3-3 clamps drop. The potassium card bounces with “That’s NLRP3’s trigger, not pyrin’s — 3.6”; the bacterium card bounces with “Pyrin doesn’t recognize the germ itself; it notices what some germs’ toxins do to RhoA”; more pyrin changes nothing while the clamps hold. Step 2, assemble: the freed pyrin meets ASC near the microtubule hub (in ordinary cells this step needs intact microtubules — Scene 5); the student joins PYD to PYD, and ASC filaments grow into one bright speck — a label reads ONE SPECK PER CELL. Step 3, switch on: the student docks pro-caspase-1 on ASC’s CARD end and it becomes caspase-1, drawn as scissors. Step 4, cut: caspase-1 cuts pro-IL-1β (“Module 2.6 taught this cut”), pro-IL-18 and gasdermin D; the gasdermin pieces fly to the membrane and open pores, and the IL-1β OUT meter climbs as IL-1β leaves through them; a side note says neutrophils often release IL-1β this way while staying alive, and that sometimes the cell bursts (pyroptosis). Step 5, the variant: a toggle labeled THE TEXTBOOK FMF VARIANT lowers the THRESHOLD meter — now the clamps let go after a smaller dip in RhoA, or when the tags come off with no toxin at all (dephosphorylation alone is enough). The same five parts, the same speck, sooner. A locked card in the corner: “Her own changed copy — where it sits and what one copy can do is Module 4’s question.” Reveal card: the parts are all normal; only the threshold for snapping them together sits too low. Keyboard path: Tab moves switch → cards → parts shelf → bench; Space picks up a part, arrow keys move it, Enter docks it; every change is announced in a polite live region (“Second phosphate tag removed; 14-3-3 released”). With prefers-reduced-motion the steps advance as stills. A <details> text version gives the five steps, the three wrong answers and why each fails. Alt text for the static view: a workbench inside a cell with a RhoA switch, a pyrin token held by two tags and two clamps, a shelf of ASC, caspase-1, pro-IL-1β and gasdermin-D pieces, and green rails across the bench.

Think · not graded

Pyrin sits ready in the cytosol the whole time, tagged and clamped while RhoA is active. Why might a cell build an alarm that watches one of its own normal processes (RhoA working) instead of one that recognizes a germ directly? And what would a sensor whose clamp lets go too easily do in a tissue with no germ in it at all?

The true/false spot-check for this prompt is in production.

Check · Drag and Drop

Drag each label to the place in a neutrophil where it happens. Text labels on a labeled cell drawing — no image hotspots.

This self-scoring check is in production.

Evidence card 4

Add it to your evidence board

The follow-up: “the pathology report was back and the appendix was normal” — a report on the organ that came out.

Scene 5 of 6

Rails for the Alarm

The cell’s railway is the most important real estate in the story: it holds the crawling cell’s front and back, and in ordinary cells the alarm can’t assemble without it — and an ancient drug pulls up the track.

Narrated slide · in production · 1 min 14 s

Rails for the Alarm

Amy’s narrated slide, Microtubules Move the Neutrophil (eyebrow THE CYTOSKELETON; “The cell’s rails”; bullets Internal rails · Drive movement · Essential · Colchicine’s target): microtubules “are not just a skeleton like we think of our skeleton… Microtubules are actually like an internal railway system”; “they disassemble some of their scaffolding and assemble it over here” as the cell moves; “a very important real estate problem in our cells”; “these microtubules are the exact target of our medicine”; “The next slide kind of pays us off.” Caption lines under the player (each also a timed caption cue at the moment it is spoken): (1) In a crawling neutrophil actin pushes the leading edge; microtubules hold the cell’s front and back (in a crawling neutrophil the centrosome sits behind the nucleus) and position organelles (notes-digest SCI 14; 3.3 Scene 5). (2) In ordinary cells the pyrin speck needs intact microtubules (Gao et al. 2016; Van Gorp et al. 2016); how they help is still being worked out, and FMF variants depend on them less. (3) “Our medicine” means the medicine used for FMF (cue at “the exact target of our medicine”); nobody prescribes it in Stina’s story until 2026, and the next slide in the deck is not played here — its payoff is the card beside the player. Card beside the player, in the narrator’s voice: colchicine binds free tubulin dimers (at the colchicine site between α- and β-tubulin); the bound dimer caps a growing end, so new rails can’t grow. In ordinary cells that blocks pyrin-inflammasome assembly; it also weakens neutrophil sticking and crawling — and in FMF the second half may matter most, because the variants need the rails less in cell studies (Van Gorp et al. 2016). How colchicine prevents FMF attacks is not fully settled. It comes from the autumn crocus, Colchicum autumnale (meadow saffron, not a true crocus), and remedies from the plant for swollen joints go back to antiquity. Its dose window is narrow; a pump, P-glycoprotein, throws it out of cells and CYP3A4 in the smooth ER clears it (3.6). It acts on the cell, not the code.

Prefer the full lecture? Non-Protein-Making Organelles (original video on the site)

Explore · in production

Switch the yard

A rail yard seen from above, drawn inside the outline of a neutrophil: a round hub near the nucleus labeled CENTROSOME (the microtubule organizing center, 3.3) with track running out from it like spokes; switch points where tracks fork; two sidings at the cell’s edge holding small cars — purple PYRIN cars (already released, Scene 4) and teal ASC cars; a depot beside the hub labeled SPECK YARD; and at the top edge a FRONT marker that the cell is trying to crawl toward. A supply depot at the bottom holds stacks of TUBULIN rail sections. This yard is about whether the track is there, not about the growing and shrinking of single tracks (3.3 built that). A banner stays in view: the cars are a model — in ordinary cells the pyrin speck needs intact microtubules (Gao et al. 2016; Van Gorp et al. 2016), but how the rails help is still being worked out, and nobody has shown pyrin and ASC riding them together. Round 1, predict: “In an ordinary neutrophil, will a speck form if the track is gone?” — yes · no · only near the edge. Then the student throws switch points to connect the sidings to the speck yard by the hub. With the track laid, a speck lights in the speck yard and the IL-1β counter ticks; with the track pulled up, the ordinary-pyrin yard stays dark. Round 2, steering: the FRONT marker moves; the hub stays behind the nucleus; with its tracks intact, the cell keeps a steady front and tail as actin pushes toward the new marker — remove track and the cell loses its axis and wanders (a label: actin pushes the edge; the rails hold front and back). Round 3, colchicine: a token labeled COLCHICINE — THE MEDICINE USED FOR FMF (NOT IN STINA’S STORY UNTIL 2026) lands on the supply depot. Before anything moves the student predicts what will fail first. Then: colchicine-bound tubulin can’t be laid as new track; sections that wear out aren’t replaced; the yard thins. In this ordinary-pyrin yard the speck yard dims, the cell loses its front and tail, and the crawl wanders: two meters drop — SPECKS FORMED and CELLS REACHING THE LINING. Round 4, compare: a toggle runs three yards side by side for one minute each — ordinary pyrin, the textbook FMF variant (released more readily, so more specks), and the textbook variant with colchicine: this variant needs the rails less (Van Gorp 2016), so some specks still form — but grip and crawl fail, so fewer cells reach the lining. Card: how colchicine prevents FMF attacks is not fully settled; stopping neutrophils from sticking and migrating is very likely a large part of it. A locked card: “Her own changed copy — Module 4.” A last card, “On the cell, not the code”: the MEFV recipe in the nucleus is untouched in every run; take the token away and the yard rebuilds — which is why a drug like this is taken daily, not once. Keyboard path: Tab moves hub → switch points → depot → toggles; Enter throws a switch, arrow keys move the FRONT marker, Space drops the colchicine token; track changes and meter changes are announced in a polite live region (“Track connected to the speck yard — one speck”). With prefers-reduced-motion each round shows as labeled stills. A <details> text version gives each round’s setup and result as a table. Alt text for the static view: a rail yard inside a cell outline — spokes of green track running from a central hub, purple and teal cars on sidings, and a dark depot labeled speck yard beside the hub.

Think · not graded

Colchicine never touches pyrin, ASC, caspase-1 or IL-1β; it binds tubulin. Using the rails, explain two ways a drug aimed at the scaffold could quiet an alarm — through the speck and through the crawl — and which one is more likely to matter for an FMF variant that needs the rails less. Then say why a drug that acts on the cell rather than the code has to be taken again and again.

The true/false spot-check for this prompt is in production.

Check · Sort the Paragraphs

Put colchicine’s action in order, from the pill to the patient — the medicine used for FMF, in the narrator’s voice.

This self-scoring check is in production.

Evidence card 5

Add it to your evidence board

Fourteen: “Two Tylenol take the edge off for about an hour, and then it comes back” — the only medicine her diary names in these years, besides the school nurse’s aspirin at thirteen.

Scene 6 of 6

Sterile

Same place, same fever, new scar: an appendicitis can’t come back after the appendix is gone — Chart Clue #3.

Animation · in production · 2 min 20 s

Sterile

A title card in the diary’s hand: Three weeks later. A body outline with a fresh scar low on the right, and the same place glowing again, the same fever on a thermometer, and a closed mouth — she doesn’t tell anyone. Inside the glow: the peritoneal lining, neutrophils rolling, sticking and squeezing in from a small vessel exactly as in Scene 3; inside one of them a speck lights and IL-1β leaves through pores. A culture plate slides in under the lining, labeled WHAT A CULTURE ASKS: does anything grow? Nothing does. Then the attack ends on its own: the glow fades over a few days, the neutrophils die quietly and macrophages clear them, and the lining is calm. Three cards line up — INFECTION (a germ; a culture that can grow it; antibiotics change the course) · AUTOIMMUNE (antibodies or T cells aimed at the body’s own tissue) · AUTOINFLAMMATORY (innate cells firing from the inside; no germ, no autoantibodies) — and the glow settles on the third. The chart’s undated row slides in: Every workup — doctors look for infection and find nothing; beneath it, What the chart said: “An infection we cannot find.” The word cannot is underlined, then the underline moves to the word find. The row pins to the course timeline as a long bar with no date, and the appendix at fifteen sits inside it as one dot. Caption: Sterile is an answer, not a dead end.

Prefer the full lecture? Immunity: Barriers, Fever and Inflammation (original video on the site)

Explore · in production

Keep the ledger

An open accounts ledger on a desk, two columns ruled in ink: INFECTION on the left, AUTOINFLAMMATION on the right, with a narrow center column headed FITS BOTH. Ten entry slips wait in a tray, each a line from the diary or the chart, dated as canon dates them: “It starts under my belly button and slides down low on the right” (11) · “they said it wasn’t my appendix, it was a stomach bug” (11) · “By Sunday I was fine… leaves like somebody switched off a light” (11) · “Day one of my period: the fever” and “four weeks later it happens again” (15) · “It’s on my calendar” (15) · “fever, pain low on the right, white count up” (15) · “the appendix was normal. ‘Unremarkable’” (15) · “probably an early appendicitis that settled down or a virus” (15) · “Three weeks later — The pain came back. Same place, same fever, new scar” (15) · “Every workup… doctors look for infection… and find nothing” (chart, undated). For each slip the student predicts a column, then drops it, and the slip asks one test question before it settles: “Would an infection do this?” and “Would autoinflammation do this?” The answers are written plainly and none is a verdict on its own. White count up → FITS BOTH (neutrophils rise either way; Scene 1). A stomach bug → INFECTION, with a note: possible at eleven, but a bug doesn’t keep a calendar for years. Fine by Sunday, like a light switch → leans AUTOINFLAMMATION (self-limited attacks that end on their own are the pattern; an untreated bacterial infection usually doesn’t switch off in a day or two). Day one of the period, every four weeks → leans AUTOINFLAMMATION (menstruation is a recognized trigger of FMF attacks — the 3.9 evidence page cites the studies; germs don’t follow a cycle). Normal appendix → leans AUTOINFLAMMATION, with the honest caveat that an early appendicitis can be missed. Probably an early appendicitis or a virus → INFECTION, the chart’s own reading. Same place three weeks later, with the appendix gone → leans AUTOINFLAMMATION (an appendicitis can’t recur without an appendix; a lining can). Every workup, nothing found → leans AUTOINFLAMMATION, and opens a side panel, WHAT A NEGATIVE CULTURE CAN PROVE: four switches — sampled the wrong place · antibiotics given first · a germ that won’t grow on a plate · a virus (not cultured routinely) — each one weakens a single negative result; then a REPEAT slider stacks negatives across years, attacks and sites, and a line reads: one negative is weak evidence; a lifetime of them, with this pattern, is a finding. A trap slip, added last: “Autoantibodies against the appendix” — dropping it anywhere returns “Not in her chart, and not this disease: that would be autoimmunity.” When the tray is empty the ledger totals each column, and the student writes the chart entry from phrase tiles — “Inflammation with no pathogen found” · “recurring on a calendar” · “ending on its own” · “in the same place after the organ was gone” — while two decoy tiles wait (“An infection we cannot find.” · “A lot of stress at home.”). The finished line becomes Chart Clue #3, and the student pins it to Module 1’s course timeline: the pin won’t take a single date and stretches into a bar, with the appendix at fifteen as one dot inside it. Keyboard path: Tab to a slip, Space picks it up, arrow keys choose a column, Enter drops it; the test answers and the side panel are read in a polite live region; the REPEAT slider is a native range input. A <details> text version lists every slip, the column it leans toward, and the one-line reason. Alt text for the static view: an open ledger with three ruled columns — Infection, Fits both, Autoinflammation — and a tray of handwritten slips below.

Think · not graded

A single negative culture can be wrong for half a dozen reasons. Name two. Then explain why the same negative, coming back attack after attack for years — with fevers that start on a calendar, end on their own and return to the same place after the organ is gone — becomes evidence rather than a dead end. What exactly does the word “sterile” claim, and what does it not?

The true/false spot-check for this prompt is in production.

Check · Single Choice

Fifteen: fever, pain low on the right, white count up; a normal appendix; three weeks later the same pain in the same place — and in every workup, the chart says, no infection is found. Which question is worth asking next?

This self-scoring check is in production.

Evidence card 6

Add it to your evidence board

“Three weeks later — The pain came back. Same place, same fever, new scar. I didn’t tell anyone.”

4

Your evidence board

Every scene gave you an evidence card, and the chart adds more. Sort each card into the column it supports: Sterile inflammation from inside her own cells, Neither on its own, or An infection we cannot find. Some cards can honestly go in more than one place — that’s allowed, and the feedback tells you which cards decide the case.

Evidence board · drag and drop · in production

The sorting board for this chapter’s cards is being built. Until it arrives, sort your evidence cards on paper into the three columns above.

5

Your verdict

Time to decide. Look back at your bet, then build your verdict from statements that hold up — no writing needed.

Look back at your prediction

Fever, pain low on the right and white count up; a normal appendix; the same pain three weeks later; and in every workup, no infection found — read through the neutrophil, the reading that fits best is…

Find the one you chose at the top. Does the evidence support it, refute it, or revise it?

  • “Probably an early appendicitis that settled down or a virus”
  • Real inflammation in the lining, with no germ in it
  • “Appendectomy; appendix unremarkable” — the organ is out, so the problem should be over

Build your verdict · no writing

Choose the statement that holds in each set. The ones you keep become your argument.

This activity is in production.

6

The finding

Finding · Chart Clue #3

Sterile Is the Clue

1990, age fifteen: fever, pain low on the right, white count up — “textbook” — and an appendix that pathology called normal; three weeks later, the same pain in the same place, told to no one. Every workup (undated in the chart): doctors look for infection and find nothing — “An infection we cannot find.” Chart entry: Chart Clue #3 — sterile inflammation, inflammation with no pathogen, is itself the clue. A white count rises with neutrophils whether or not a germ called them; neutrophils roll, stick, squeeze and crawl into a lining on signals the tissue makes itself; and inside them pyrin — a sensor that in FMF lets go too easily — builds its alarm and sends IL-1β out through gasdermin-D pores. This was autoinflammation, driven from inside her own cells: not autoimmunity, and not a missed infection. Held open: no culture and no lab value is recorded for 1986–1990; nobody sampled her peritoneum in 1990; one negative culture is weak evidence on its own; and what her own changed copy of pyrin does is Module 4’s question.

Next · Module 3 conclusion

Module 3 · Conclusion and Assessment

Fifteen: an appendix called unremarkable and a pain that came back to the same place. Seven chapters of cell biology come down to one question for the whole chart — an infection we cannot find, or an alarm with no intruder? Replay the fifth visit as a cell consult, sort what was measured from what was said, and pin Chart Clue #3 to the course timeline. Finish The Cell & Its Transport →

Continue to the Conclusion →

Reliable information on rare diseases

NORD · NIH GARD · Orphanet · MedlinePlus Genetics: FMF · FMF & AID Global Association · Autoinflammatory Alliance · Global Genes · Amyloidosis Foundation

Stina has one rare disease. In the United States, about 1 in 10 people live with one of the more than 7,000 known rare diseases. These organizations are where patients, families and clinicians go for trustworthy information.

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← Familial Mediterranean Fever — case home

All pages for Module 3 — The Cell & Its Transport

3.0 Module Overview
3.1 The Membrane
3.2 Meet the Cells
3.3 Organelles and the Scaffold
3.4 The Protein Factory and Its Two Exits
3.5 Osmosis, Tonicity, Effusion
3.6 Pumps, Channels and Voltage
3.7 Inside the Neutrophil
3.8 Conclusion and Assessment
3.9 The Evidence Behind the Case

All Modules
  1. Anatomical Language, Membranes & Homeostasis
  2. Just Enough Chemistry
  3. The Cell & Its Transport
  4. Making Cells & Proteins
  5. The Integumentary System
  6. The Skeletal System
  7. The Muscular System
  8. Nervous Tissue & the Senses
  9. The Spinal Cord
  10. The Brain & the Blood–Brain Barrier
  11. The Autonomic Nervous System
  12. Special Senses (in development)
  13. The Endocrine System
  14. Blood
  15. The Heart
  16. Blood Vessels
  17. The Digestive System
  18. The Respiratory System
  19. The Urinary System
  20. Fluids, Electrolytes & Acid–Base Balance
  21. The Reproductive System
  22. The Immune System

List of terms