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by two different types of cell surface complexes, called MHC complexes. This difference in recognition, class I or II, is one difference between CD4 (helper) and CD8 (cytotoxic) T cells. Cytotoxic T cells release cytotoxins that kill infected or damaged host cells. Helper T cells secrete cytokines, which are more chemicals, to activate other cells in the immune response.

Some lesser known subsets of T cells are memory T cells, which are antigen-specific, and therefore invading-organism-specific, and are part of the long-term immune response. The cells recognize later infections by the same agent and can promote a faster response. Regulatory T cells, also known as suppressor T cells, suppress the immune response to prevent over activity against the host.

B cells are activated in a two step process of engulfing the foreign particles and recognizing them on their own surface. Plasma cells are mature B cells that make antibodies against those specific antigens. Antibodies are proteins that bind to the surface of a cell to mark it for destruction by other components of the immune response (called complement). Memory cells are long-term activated B cells that can quickly begin antibody production against re-infection by the same pathogen. Some antibodies are produced as a first line of defense in the mucus membranes, other specifically to attack an invading particle or organism.

Learn more about this author, Alicia M Prater PhD.
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