Major histocompatibility complex antigens stimulation

Quiescent T lymphocytes are stimulated largely by direct binding to an antigen fragment presented on the surface of a macrophage in the context of major histocompatibility complex (MHC) (Figure 5.3). This results in the induction of expression of at least 70 genes whose products are collectively important in immune stimulation. These products include ... 

To initiate a T-cell immune response, antigen presenting cells have to display antigenic peptides com-plexed with the major histocompatibility complex (MHC) on their cell surface. The T-cell receptor of CDS cells is specific for the peptide-MHC class I complex while the CD4 cell receptor binds the peptide-MHC class II complex. This binding of the peptide-MHC II complex stimulates CD4 cell proliferation and subsequent lymphokine release. This CD4 cell response can initiate a delayed hypersensitivity reaction. However CD4 activation and the production of various lymphokines is also needed for the generation of cytotoxic T-cells and for the differentiation of plasma cells from B-lymphocytes and the antibody response by these plasma cells. For their role in also the humoral immune response CD4 cells are called T-helper cells. 

Suppressor lymphocytes control immune responses in part by secretion of an antigegjspecific factor which is not active across histocompatibility barriers. This product has a molecular weight between 35,000 and 55,000 daltons and can be completely absorbed with an alloantiseruij2 specific for the I region of the major histocompatibility complex. A soluble immune response suppressor (SJ S) is produced by concanavalin A-stimulated murine splenic lymphocytes and inhibits plaque-fcjjjming responses of B lymphocytes and cytotoxic lymphocyte responses t allo-antigens. SIRS has a molecular weight between 48,000 and 67,000, does... 

U2, Uchiyama, T., Saito, S., Inoko, H., Yan, X, J., Imanishi, K., Araake, M., and Igarashi, H. Relative activities of distinct isotypes of murine and human major histocompatibility complex class 11 molecules in binding toxic shock syndrome toxin 1 and determination of CD antigens expressed on T cells generated upon stimulation by the toxin. Infect. Immun. 58, 3877-3882 (1990). 

Fig. 18.1-6 T helper cell differentiation. Thl and Th2 cells develop from a common precursor, the naYve CD4+ T cell. Nai ve CD4+ T cells differentiate into T helper type 1 and T helper type 2 (Thl and Th2) cells that protect against microbial pathogens by producing cytokines that mobilize appropriate defence mechanisms. The differentiation process is initiated by stimulation oftheT-cell receptor (TCR) on the naive CD4+ T cell with a peptide-major histocompatibility complex (MHC) complex on an antigen-presenting cell (APC).

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