Antigens thymus-dependent

This class of lymphocytes differentiates from immuno-logically incompetent hematopoietic stem cells of the bone marrow within the thymus - hence, the name thymus-dependent (T-) lymphocytes. Two major subclasses develop simultaneously, T-helper lymphocytes (Th) and cytotoxic effector lymphocytes (Tc). The cytotoxic T-lymphocytes (carrying on the surface the differentiation marker CD8) destroy cells, which cany their cognate antigen bound to MHC class I molecules on the surface by inducing apoptosis. From an evolutionary point of view Tc cells appear to have developed predominantly to cope with vims infections. As vituses can only replicate within cells, Tc eliminate them by destroying their producers. 

Mechanism of Action Antibodies of multiple specificities interact with lymphocyte surface antigens, depleting numbers of circulating, thymus-dependent lymphocytes and interfering with cell-mediated and humoral immune responses... 

Thymus-dependent antigens are those in which antibody production requires thymus-derived (T) cell participation, i.e.. serum proteins. Thymus-indcpcndcnt antigens do not require this participation, i.e.. polysaccharides, such as endotoxins. 

T-lymphocyte (thymus dependent T-cell) A type of lymphocyte involved in cellular immune reactions and aiding in the production of antibodies. They originate in haemopoietic stem cells, but undergo essential maturation in the thymus gland. They interact with other cells (e.g. B-lymphocytes) and e.g. antigens, lymphokines via receptor sites on their membranes. There are several subsets of T-lymphocytes see cytotoxic T-cells helper T-cells inducer T-cells suppressor T-cells. 

In order to fully understand the complex biochemical mechanisms by which the thymus and its hormones control the expression of immunity, it is first necessary to review briefly the organization of the thymus-dependent (T cell) immune system (Fig. I). The predominant cells of the peripheral lymphoid tissue (i.e., spleen, lymph nodes) includes both B and T lymphocytes. In the presence of foreign antigens, B lymphocytes differentiate into plasma cells, which in turn synthesize antibody thus, B cells make up the humoral arm of the immune system. In contrast, T lymphocytes are responsible for mediating all the classical cellular immune responses such as delayed type hypersensitivity skin responses, organ transplant rejections, and sensitized antitumor immunity as well as immunity toward various viral, fungal, and protozoal pathogens (Reinherz and Schlossman, 1980). 

One of a series of arylhydroxytriazenes, PR-H-986 BS (JL) was effective in both hvimoral and cell-mediated immune responses and in rat adjuvant-induced arthritis.97 The orally active antiviral agent tilerone (2), effectively inhibited symptoms of adjuvant arthritis and allergic encephalomyelitis in rats but paradoxically, it potentiated the humoral immune response to the thymus dependent and Independent antigens as well as to homocytotropic antibody.98... 

MILLER NW, CLEM Lw (1984), Temperature-mediated processes in teleost immunity differential effects of temperature on catfish in vitro antibody responses to thymus-dependent and thymus-independent antigens , / Immunol, 133,2356-9. 

In summary, although numerous AhR-dependent changes in the bone marrow and thymus have been found in TCDD-treated mice, it appears that these effects are self-limiting in adult mice, as T and B cell numbers are not reduced in secondary lymphoid tissue except after exposure to high doses of TCDD or in the context of an adaptive immune response. More subtle effects, such as changes in the antigenic specificity of peripheral T and B lymphocyte populations, have not been documented. 

In addition, a distinction is made between cellular and humoral immune responses. The T lymphocytes (T cells) are responsible for cellular immunity. They are named after the thymus, in which the decisive steps in their differentiation take place. Depending on their function, another distinction is made between cytotoxic T cells (green) and helper T cells (blue). Humoral immunity is based on the activity of the B lymphocytes (B cells, light brown), which mature in the bone marrow. After activation by T cells, B cells are able to release soluble forms of their specific antigen receptors, known as antibodies (see p. 300), into the blood plasma. The immune system s memory is represented by memory cells. These are particularly long-lived cells that can arise from any of the lymphocyte types described. 

Nitschke, L., Kosco, M.H., Kohler, G., Lamers, M.C. (1993). Immunoglobulin D-deficient mice can mount normal immune responses to thymus-independent and -dependent antigens. Proc. Natl. Acad. Sci. USA 90, 1887-1891. 

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