Immunity: Antimicrobial Proteins

Cytokines
& Interleukins

Cytokines include several subtypes such as interleukins, interferons, tumor necrosis factors (TNFs), and growthAn increase in size and number of cells. factors, among others. Interleukins (ILs) are a specific type of cytokine. Interleukins are numbered (IL-1, IL-2, IL-3, etc.), with each number representing a specific interleukin that has different functions.

The term “interleukin” comes from “inter” (meaning between) and “leukin” (meaning white blood cell). They are mainly produced by and act on white blood cellsThe basic structural and functional units of life. (leukocytes). Cytokines are like communication between cells.  These proteinsLarge molecules made of amino acids with various functions in the body. can recruit more immune cells like neutrophils to leave the blood stream and come to an infected area.  Some interleukins tell neutrophils to stop their processes so that tissue repair can begin.

Shows you how these types of T cells in the left hand column secrete different interleukins. The interleukins have a variety of effector cells. These include basophils, neutrophils, and dendritic cellsImmune cells in the epidermis that help fight infections.. They recruit them to come to the injured area and help amplify the immune response in positive feedbackA control mechanism that amplifies a change instead of reversing it.. Just one of these T cells can recruit thousands of these effector cells period

Interferons

Interferons are proteins secreted by infected cells in a last ditch effort to save adjacent uninfected cells from viral attack. Interferons diffuse into adjacent cells. They trigger the still healthy cell to synthesize proteins. These proteins stop viral protein synthesis and degrade the viral RNA.

Interferons are chemicals secreted by various cells, playing a vital role in immune communication. They are part of a broader category of cell secretions known as cytokines. Alpha interferons, produced by virus-infected cells, act as alarm signals to attract NK cells. Beta interferons are secreted by fibrocytes and connective tissue cells. They regulate inflammation and start repair processes. This is particularly the case in autoimmune conditions rather than infections. Gamma interferons, secreted by damaged skinThe body’s largest organ, providing protection and regulation. cells, stimulate macrophages in the dermisThe thick inner layer of the skin that contains blood vessels, nerves, and connective tissue., further supporting the immune response.

Complement

The complement system consists of a set of at least twenty plasmaThe liquid component of blood. proteins. These proteins circulate in the blood when they are inactive. The complement proteins have four main functions; mediate inflammation, cause cell lysis, attract phagocytes, and facilitate phagocytosis. Complement can be activated in two ways. One is by antibodies. Another way is when certain complement factors interact with microbial moleculesGroups of atoms bonded together. and target them for destruction.

Complement proteins can be activated in more than one way.  The classical pathway is the faster of the two and is antibody-based.  The alternative pathway is slower and tends to be used for parasitic infections or viruses.  The result of both pathways includes enhancing inflammation, initiating cell lysis, attracting phagocytes to the area, and promoting phagocytosis.

Complement proteins mediate inflammation by stimulating the release of histamine by Mast cells and basophils.  This powerful vasodilator increases the ability of leukocytes to come to the area.

The complement system also uses lysis.

 The complement proteins bind to the antibodies and are then fixed or embedded into the target cell membrane. A group of complement proteins called the membrane attack complex, or MAC for short, are inserted into the cell membrane. The membrane attack complex makes a pore in the target cell membrane, inducing a massive influx of waterThe universal solvent essential for life..

Complement proteins can attract phagocytes to the area of infection. This is called opsonization.  The root word for opsonization means “condiment.”  Just as ketchup, or whatever your chosen dipping sauce is, complement can make a pathogen more tasty to macrophages. 

A product of complement activation is called C-reactive protein or CRP. CRP is produced by the liverA large organ that produces bile, detoxifies blood, and stores nutrients. in response to inflammatory molecules. CRP has useful clinical applications. For instance, physicians use it as a marker to determine acute infection or inflammation. They can also gauge how well a patient responds to treatment by measuring the levels of CRP.