Innate Cells

Lymphoid Cells

For the blood chapter, we understand that the master stem cell is responsible for creating all of our white blood cellsThe basic structural and functional units of life.. It also creates our red blood cells. This cell is called a hematopoietic stem cellA multipotent stem cell that gives rise to all blood cells.. This stem cell can divide into two other quasi type stem cells. These cells can then differentiate into the final cells. These are the cells we see in tissue and blood.

We have discussed this myeloid stem cell earlier. It gives rise to the erythrocytes(RBCs): Red blood cells responsible for oxygen transport. and four out of the five leucocytes. It also gives rise to platelets. We have talked about macrophages cells that eat debris and other cells. I have mentioned dendritic cellsImmune cells in the epidermis that help fight infections. which are cells that drink fluids in order to ingest debris or other cells. Both macrophages and dendritic cells derive from monocytes. These monocytes float in the blood. They decide to exit and take residence in a certain tissue.

What we haven’t previously discussed is a lymphoid stem cell. It is capable of dividing into T cells, B cells, and natural killer cells. These cells are also known as NK cells. T cells can divide into a whole bunch of more versions. B cells can divide into plasma cellsImmune cells that develop from B cells and produce antibodies. that create antibodies.

Phagocytes

The term phagocytes just refers to cells that eat things.  More specifically, there are macrophages, derived from monocytes, and there are microphages.  Microphages are neutrophils and eosinophils that circulate in blood and are summoned to a tissue only when needed.  You can see this neutrophil here phagocytozing some bacteria and some other foreign type cells. 

Phagocytes encounter a pathogen or debris. They surround it with their cell membrane. They ingest it into a small compartment known as a phagosome. This process is called endocytosisThe process of a cell engulfing material by wrapping its membrane around it.. The phagosome then fuses with a lysosomeAn organelle filled with digestive enzymes that break down waste and cellular debris., which contains enzymesProteins that speed up chemical reactions in the body. that break down and digest the material.  Macrophages and dendritic cells have a special ability. They can present the antigensMolecules on the surface of cells that trigger an immune response. of the pathogen to B and T cells in lymph nodes.  This is a process called antigen-presentation and is discussed in another mini-lecture

Macrophages

Monocytes are white blood cells that derive from the myeloid stem cell. Monocytes float around in the blood however they don’t spend the entirety of their life in blood circulation. Monocytes will move into tissues in the body and take up residence there. Once there we usually give them a more specific name.

You might not have realized this, but osteoclasts are cells capable of breaking down bone. They are not derived from the other stem cells that own cells come from. OsteoclastsBone-resorbing cells that break down bone matrix. are actually a monocyte that has moved into bone to take up permanent residence. In the brain, you have microgliaSmall CNS glial cells that act as macrophages, cleaning up debris and pathogens.. In the liverA large organ that produces bile, detoxifies blood, and stores nutrients., there are cells called cup for cells, and in your lungs, you have cells called alveolar macrophagesImmune cells found in the alveoli that engulf and digest pathogens, debris, and dust particles.. There are tons of different macrophages in the spleen, not just the four that are listed here.

Mast Cells

Mast cells are important to us.  Mast cells reside in tissues instead of floating around in blood.  Mast cells release histamine and heparin in response to encounters with pathogens.  Histamine induces vasodilationThe widening of blood vessels due to relaxation of smooth muscle, decreasing blood pressure and incr and draws more immune response cells to the site of injury more quickly. In addition, histamine slows the spread of pathogens by causing capillary plasmaThe liquid component of blood. to leak. Clotting proteinsLarge molecules made of amino acids with various functions in the body. also leak into the tissue spaces.

Therefore, the greater the concentration of histamine released, the greater the inflammatory response. Mediation of inflammation through complement serves to temporarily repair the tissue and prevent additional pathogens from entering the wound. It slows the spread of pathogens from the site of injury or infection.