Phenotypic and Functional Heterogeneity of Double Negative (CD4-CD8-) αβ TcR+ T Cell Clones
The CD4 and CD8 T cell markers are useful phenotypic landmarks which in general terms divide the T cell pool into those cells which aid B cell responses and T cells with cytotoxic capabilities. CD4+ T cells respond to antigen in the context of class II MHC and are predominantly helpers of B cell responses whereas CD8+ T cells are stimulated by antigen in the context of class I MHC and function as cytotoxic T cells. It has been assumed that all mature T cells express either of these markers, however, recently a T cell subpopulation has been described which lack both CD4 and CD8. The majority of these double negative T cells bear the alternative γδ T cell receptor (TcR) with between 7% (Bender and Kabelitz, 1990) and 38% (Scott, 1990) being αβ T cell receptor positive. T cells with this phenotype are known to exist in the thymus but are thought to be immature and destined to either die or differentiate into mature single-positive (CD4+ CD8− or CD4− CD8+) T cells. Therefore their existence in the periphery indicates either the existence of a novel mature T cell subset or leakage of immature cells from the thymus.
KeywordsArthritis Chromium Nephritis
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