What are Cytokines?

 

Q: What are Cytokines?
Cytokines are signaling molecules produced by immune system cells. These molecules help different branches of the immune system talk to each other and respond to threats. After cells release them, they bind target receptors on other cells to alter cell function. The molecules can ramp up the immune system or tone it down.
Examples of cytokine types include colony-stimulating factors (CSFs), interferons (IFNs), interleukins (ILs), and growth factors (Table). Covered here are the most clinically relevant cytokines and their functions.
Cytokines are released in response to an interaction between T cells, an antigen-presenting cell (e.g., a macrophage or dendritic cell), and an antigen that stimulates an immune response. The cytokines produced depend on the type ofT cell involved (termed a ‘T-cell subset’) and the cytokine profile of that subset.
Major subsets include T-helper ThO, Th I, Th2, and Th 17:
ThO cells are unrestricted. They are naive T cells that can respond to novel antigens that the immune system has not yet encountered.
Th1 cells produce IFN-gamma, IL-2; are important in cell-mediated immune response (e.g., delayed-type hypersensitivity reaction); and are stimulated by the IL-12 superfamily.
Th2 cells produce IL-4 , IL-IO; are important in humoral immune response (antibody development and allergic responses); and are stimulated by IL-4, IL-I 8, and IL-33, working together.
Th17 cells produce IL-17 A, IL-l 7F, IL-22; areimportant in antifungal immunity and also autoimmune-related chronic inflammatory diseases (e.g., rheumatoid arthritis, inflammatory myopathies); and are stimulated by IL-I, -6, -21, -23.
Cytokines that mediate cellular migration into tissue are called chemokines. IL-8 is an example. Some cytokines that inhibit the immune system are prostaglandins, transforming growth factor (TGF)-beta, and IL-10. Unregulated cytokine activation contributes to the systemic inflammatory response syndrome (SIRS), which is a severe condition with systemic inflammation and organ dysfunction and failure. SIRS is diagnosed if any 2 of the following parameters are present: temperature > 38 or < 36; heart rate > 90; respiratory rate > 20; WBC > 12.0 or> I 0% bands on peripheral smear.
SIRS may have an infectious or a noninfectious etiology. When infection is suspected or demonstrated, the condition is called sepsis. Tumor necrosis factor (TNF)-a may be the most important mediator. TNF-a is a cytokine released by neutrnphils, monocytes, and macrophages in response to endotoxin (lipopolysaccharide; LPS). Once released, TNF-a amplifies the signal LPS and transmits it to other cells.
Table : Cytokines
Type Functions
Interleukins
IL-1 Fever, stimulates T cells
IL-2 Proliferates T cells, activates B cells
IL-4 Immunoglobulin switch signal,
suppresses Th 1
IL-6 Cell proliferator, acute-phase reactant
IL-12 Increases IFN-gamma, induces Th1
differentiation
IL-15 Induces TNF-alpha release
IL-17 Important in autoimmune chronic
inflammatory reactions and anti-fungal
immunity.
TNF-alpha Cachexia, stimulates T cell
IFN-gamma Activates T cells, NK cells,
macrophages
TGF-beta Inhibits T-cell proliferation and
pro-inflammatory cytokines

Platelet-derived growth factor

Proliferates fibroblasts
Reference : Internal Medicine

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