Cells of Immune System: Development, Activation, Effector Functions

While understanding the role of certain cell populations and subpopulations is being more precisely identified, the pool of immunocompetent cells becomes continuously broader. It has rather recently been shown that hematopoietic precursors that express CD34 on their surface may be served as precursors of both monocytes/macrophages (Mn/Mf), and dendritic cells (DC) Huge experimental data obtained for recent years have shown that DC may just be comprehensive APC, capable to present both bacterial, and viral antigens in both primary, and secondary immune response for recognition by both T helpers (CD4(+)) and cytotoxic T lymphocytes (CD8(+)). Both Mf, and DC are producers of cytokines. After microbe phagocytosis by Mf or after DC infection, microbe components may induce production of IL-12 in these cells followed by IL-12 induction of IFNgamma production in NK and CD4(+) T lymphocytes. IFNgamma production is highly inducible: primary steps of IFNgamma production require, at least, two activation signals: from TCR, from adhesive or costimulatory molecules or from receptor for any additional cytokine, for example, IL-12. IFNgamma is synergistic agent for IL-12 that is providing costimulatory signal in induction of Th1 differentiation and is enhancing the sensitivity of naive T lymphocytes to stimulatory action of IL-12. Either Th1, and Th2 express beta1-chain of IL-12 receptor, but only Th1 express beta2-chain of this receptor. Incapability of Th2 to respond to IL-12 by activation is related to such a situation.