On the basis of principal biologic actions; cytokines are grouped under three basic categories:
(i) Mediators and regulators of innate immunity:
These are produced mainly by mononuclear phagocytes in response to infectious agents: Pathogen-associated molecular patterns; like bacterial lipopolysaccharides (LPS) and viral double stranded RNA (dsRNA), also bind to Toll like receptors (TLRs) on the cell surface or in endosomes of macrophages and stimulate the synthesis of some important cytokines of innate of Innate immunity. They act on endothelial cells and leukocytes.
(ii) Mediators and regulators of adaptive immunity:
These are produced mainly by T-lymphocytes in response to specific recognition of foreign antigens. Some T-cell cytokines regulate the growth and differentiation of various lymphocyte populations and are related with T cell-dependent immune responses. These cytokines also regulate and activate mononuclear phagocytes, neutrophils and eosinophils.
The comparative feature of cytokines of Innate and Adaptive immunity are placed in Table 8.3.
(iii) Stimulators of haematopoiesis:
These are produced by bone marrow stromal cells, leukocytes and other cells, and stimulate the growth and differentiation of immature leukocytes. Therefore, in general, the cytokines of innate and adaptive immunity are produced by different cell populations and act on different target cells. The functions of different cytokines are mentioned in Table 8.4.
