The γ-δ Heterodimer
T cells play an important role in the mammalian immune system, participating in a number of cell-cell interactions. It is through these interactions, and the products that result from these interactions, that T cells aid in the regulation and differentiation of the immune response. T cells can be divided into those that mediate the cellular response (cytotoxic T lymphocytes) and those that regulate the humoral response (helper and suppressor T lymphocytes). Cytotoxic T lymphocytes (CTL) lyse abnormal host cells, including neoplastic cells and those infected by virus, while helper T lymphocytes (HTL) enhance the response of B cells and other T cells, and suppressor T cells down-regulate their response. T cells are closely related to B cells, which provide the fine tuning of the immune response by the production of immunoglobulins; antigen-specific molecules involved in a variety of immune reactions that lead to the elimination of antigen and the neutralization of antigen-bearing cells (Davies and Metzger, 1983; Honjo, 1983). Both B and T cells have diverse, clonally distributed repertoires, recognize antigen in a specific manner by means of cell surface receptors, and generate the genes that encode their receptors by the rearrangement of sequences that are noncontiguous in germ-line DNA, using the same enzyme system. However, there are a number of significant differences between the two cell types, including their products, specific functions, and modes of antigen recognition.
KeywordsChain Gene Gene Segment Mixed Lymphocyte Reaction Gamma Gene Cell Antigen Receptor
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