Immune response simply means, the reaction of our immune system to any foreign body entering the Human body. The processes concerned with the immune response are: Cell mediated immunity, humoral immunity, antibody dependent cell-mediated immunity, NK cells- Natural Killer cells mediated immunity, leucocytes élevés dans les urines causes and Macrophages-mediated immunity.
Cell mediated Immunity: This is mediated by the T cells.
A. Immunity against infections: Effective immunity against bacteria such as mycobacteria and listeria, certain viruses and almost all parasites is mediated by T cells. T cells from sensitized individuals lyze the target cells bearing the viruses.
B. Helper function: Helper cells (TH) are a subgroup of cells with receptors for the Fc portion of IgM (Tu). They form about 50% of the T cells of peripheral blood. They are necessary for optimal antibody production by plasma cells and for generation of cytotoxic T cells.
C. The rejection of allograft and destruction of tumor cells: These are also mediated mainly by T cells, although other mechanisms are also involved.
D. Suppressor function: The suppressor cell (TS) subgroup which constitutes 10% of the total can be separated by the presence of surface receptors for Fc portion of IgG (Tr). They regulate the activities of both T and B cells. The TS activity is depressed in many autoimmune diseases and in some of the human malignancies.
E. Production of soluble mediators: T cells, stimulated by antigens, liberate certain soluble substances called lymphokines. Lymphokines include macrophage migration inhibition factor (MIF), macrophage activation factor (MAF), leucocyte migration inhibition factor (LMIF), leucocyte adherence inhibition factor (LAIF), chemotactic factor, transfer factor and interferon. The MIF and MAF help in the accumulation of macrophages at the site of reaction. The resulting erythema and induration form the basis of skin tests. Administration of transfer factor to non-sensitized individuals leads to specific sensitization. Interferon interferes with virus multiplication in host cells.
F. Delayed hypersensitivity: When tuberculin (or a similar antigen) is injected intradermally in sensitized individual, monocytes bas an erythematous indurate lesion develops slowly, reaching its maximum within 48-72 hours. This is called delated type of hypersensitivity. Hypersensitivity is the abnormal over-reaction of the immune system and it usually results in un-wanted tissue destruction. This is responsible for caseation in the case of tuberculosis, granulomatous skin lesions in tuberculoid leprosy, rashes in smallpox and measles, skin lesions in herpes simplex, and contact hyper-sensitivity to chemicals and plants. Hypersensitivity reaction mediated by T cells is called type IV reaction.
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