From the Developmental Expression of γδ T Cell Receptors to the Implications in the Acquisition of Tolerance
T cell precursors arising from hematopoietic stem cells colonize the thymus during ontogeny, where they undergo differentiation and maturation events involving genotypic changes that result in the expression of distinct surface molecules. During this process, an ordered rearrangement and expression of the T cell receptor (TCR) genes leads to the acquisition of two distinct types of CD3 associated TCR structures, α,β and γ,δ, which are independently expressed on the surface of distinct intrathymic subpopulations. The first TCR characterized α,β is expressed on the majority of mature thymocytes and peripheral T lymphocytes, and mediates the specific recognition of antigen (peptides) in association with Major Histocompatibility Complex (MHC)-encoded class I and class II molecules. The second TCR, γ,δ is expressed early in thymic ontogeny, and in adulthood its expression is restricted to a small fraction of peripheral blood and thymic T cells. A major difference between the α,β and γ,δ TCR bearing cell subsets resides in the differential distribution of CD4 and CD8 molecules, whose expression appears to be dictated by the TCR specificity.
KeywordsMajor Histocompatibility Complex Major Histocompatibility Complex Class Major Histocompatibility Complex Molecule Clonal Deletion Double Positive Thymocyte
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