T cells are classified into CD4 (mainly cytokine-secreting helper cells, making up about 75% of peripheral blood T cells) and CD8 (mainly cytotoxic suppressor cells, which account for the remainder). These cell types are indistinguishable morphologically, but can be separated by the presence of cell-surface molecules detected by monoclonal antibodies detecting cluster of differentiation or CD molecules.

Cytotoxic/suppressor cells

The cytotoxic/suppresser lymphocyte can be recognized by the presence of the CD8+ cell surface molecule and its ability to recognize antigen only when presented with MHC class I molecules. Cytotoxic T cells kill other cells, either by inserting perforins into target cell membranes, producing pores through which granzyme is inserted and causing the action of granule-associated osmotic lysis of the cell (similar to the membrane attack complex of complement) or via activation of caspases to induce apoptosis in the target. This kind of response is used in controlling viral infections and possibly malignancies. The suppressor cell downregulates immune responses. It may function by releasing soluble factors which act on B lymphocytes to reduce their output of antibodies. CD8 cells can also mount a non-cytotoxic antiviral response (NCAR) that blocks viral replication through the secretion of CD8 antiviral factor (CAF); this has been demonstrated in HIV infection.

Helper/inducer cells

T-helper cells can be distinguished by the presence of the CD4 protein on their surface and the ability to recognize antigen only when expressed with MHC class II on antigen-presenting cells. Whereas the cytotoxic response is a simple recognition system for foreign invasion, the CD4-cell system is more elaborate, involving a limited number of cells to produce an even more specific series of reactions. T-helper cells are viewed as orchestrating the immune response. They cannot directly destroy their target, but recognize specific foreign antigen and proceed to activate other parts of the system which can eradicate it.

T-helper cells have been categorized into two major functional subpopulations based on their pattern of cytokine production. A single clone of T cells can differentiate to either type, depending on antigen route, dose, the cytokine environment in which the response occurs and hereditary tendency. The T-helper 1 (Th1) class produces IL-2, IL-3 and gamma-interferon. These cytokines will promote immune responses that are primarily cell-mediated/inflammatory by activating cytotoxic T cells, NK cells and macrophages. Cells in the T-helper 2 (Th2) category produce cytokines that favour induction of antibody responses by B cells, i.e. IL-4, IL-5, IL-6, IL-10, and are thought to be involved in the development of allergic disease.

2 Comments »

1. [...] LYMPHOID SYSTEM. T lymphocytes [...]

   Pingback by Cold and Flu Prevention Part II – With Nutrients | Helpful Health Tips — December 10, 2009 @ 1:25 am

2. [...] this new set of MHC molecules and a few have activated leading to a full blown immune response …Health Nova: Your Ultimate Medical Portal LYMPHOID SYSTEM …The cytotoxic/suppresser lymphocyte can be recognized by the presence of the CD8+ cell surface [...]

   Pingback by mhc molecules — March 18, 2010 @ 8:34 pm

RSS feed for comments on this post. TrackBack URL

Leave a comment

Name (required)

Mail (will not be published) (required)

Website