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A T lymphocyte expresses on its surface one of two types of antigen receptor, T-cell receptor alpha beta or T-cell receptor gamma delta, encoded by a pair of somatically rearranged alpha and beta or gamma and delta genes. It has been suggested that alpha beta T cells are generated only from precursor T cells that failed to rearrange gamma and delta genes in a functional form. However, we found that transgenic mice constructed with functionally rearranged gamma and delta genes produce a normal number of alpha beta T cells. The transgene gamma present in these alpha beta T cells is repressed apparently through an associated cis DNA element (silencer). We propose that some T-cell precursors are committed to generate alpha beta T cells independent of the rearrangement status of their gamma gene and that this commitment involves activation of a factor(s) that interacts with the gamma gene-associated silencer.

Three hamster monoclonal antibodies (mAbs), all recognizing different epitopes present on the native form of the murine T-cell antigen receptor (TCR) gamma delta subunits, have been generated. mAb 3A10 is specific to a pan-murine TCR gamma delta, recognizing a C delta constant region determinant. mAb 8D6 is specific to a subset of T cells expressing V gamma 4- and V delta 5-encoded gamma delta TCR, and mAb 5C10 is clonotypic. Using these and other mAbs directed against a variety of T-cell surface markers, we quantitated and characterized gamma delta T cells present in developing thymuses as well as in the conventional lymphatic organs by flow cytometry. These studies revealed that (i) many gamma delta thymocytes and peripheral T cells bear CD4 and/or CD8 molecules, (ii) T cells bearing both alpha beta and gamma delta TCRs are scarce, and (iii) thymocyte subsets bearing TCR gamma delta encoded by different combinations of V gamma and V delta gene segments appear in waves during ontogeny.