Lec.9 Cytokines

Cytokines are soluble low molecular weight proteins secreted by immune cells and act on many target cells and play an important role in the regulation of the immune response so they are chemical messengers of immune cells. Cytokines initiate their actions by binding to specific membrane receptors on target cells and alter gene expression, resulting in the new biological functions and sometimes the proliferation of the target cells. A variety of cells are capable of producing cytokines however the principle producers are T- helper cell and macrophage.

Action of Cytokines Autocrine: acts on same cell that produced it; such as IL-2 produced by T cell and cause T- cell activation). Paracrine: acts on nearby cells; T cell cytokine help for B cells activation. Endocrine: acts on cell at a distance (through bloodstream); such as Inflammatory cytokines.

Pleiotropy: one cytokine affects multiple cell types.

Redundancy: Multiple cytokines affects same type of the cells

Synergy: Two or more CKs cooperate to produce an effect that is different or greater than effect of the two cytokines when functioning separately

Antagonism: Two or more cytokines work against each other

Cytokines are classified based on the cell that produced it and their function into: Interleukins ( IL): produced by leukocyte and acting on other leukocyte. Lymphokines: produced by lymphocytes. Monokines: produced by monocytes. Chemokine: cytokine which have chemotactic activity; it stimulate attraction and migration of cells to infected areas.

Colony stimulating factor (CSF): stimulation of cell growth. Interferons (IFN): cytokine which have antiviral activity; it Protect against viral infections. Transforming growth factors (TGF): regulation of cell growth. Colony stimulating factor (CSF): stimulation of cell growth. Tumer necrosis factor (TNF): induction of apoptosis.

Cytokine functional grouping: 1.Mediators and regulator of innate immunity: IL-1, IL-6 , TNF- , IFN; act on endothelial cells and leukocytes to stimulate early innate response. Mononuclear phagocytes( such as macrophage) are the major source of cytokines of innate immunity

2.Mediators and regulators of adptive immunity: IL-2, IL-4 , IL-5, TGF- , act on lymphocyte to stimulate and regulate adaptive response. Cytokine of adaptive immunity are produced mainly by T lymphocytes in response to specific recognition of antigen.

3. Stimulators of hematopoiesis: stem cell factor (SCF), granulocyte-macrophage colony stimulating factor (GM-CSF), IL-3, IL-7, act on bone marrow to stimulate growth and differentiation of leukocyte and lymphocyte. 4. Inflammation: proinflammatory cytokines such as IL-1 , IL6 , TNF.