Selective expression of V_δ6 genes by B2A2⁻ CD4⁻ CD⁻ T cell receptor γ/δ thymocytes

Abstract Most CD4 − CD8 − adult murine thymocytes characterized by absence of the B2A2 (J11d) antigen express T cell receptors (TcR) α/β and utilize preferentially V β 8.2 segments. To a much lesser extent, B2A2 − CD4 − CD8 − thymocytes also express TcR γ/δ, as evidenced by biochemical and Northern blot analysis. We have now been able to exclude the possibility that these cells might co‐express both types of TcR: V β 8 B2A2 − CD4 − CD8 − thymocytes expressed no TcR δ mRNA whereas the corresponding V β 8 − subset transcribed full‐length TcR γ as well as δ mRNA. Furthermore, the TcR γ/δ expressing B2A2 − thymocytes were found to use preferentially V δ 6 genes. Conversely, they did not express V δ 5 genes which are most frequently used by other TcR γ/δ‐bearing populations such as B2A2 CD4 − CD8 − thymocytes or CD4 − CD8 − peripheral lymph node cells. RNase protection experiments showed that two particular V δ 6 transcripts predominate in these γ/δ populations, the most prominent V δ 6 sequence being highly homologous if not identical to V α 7.1. Our observations extend previous information on overlapping V α and V δ gene repertoires, particularly in the cross‐hybridizing V α 7/V δ 6 gene family. Moreover, our data suggest that B2A2 − CD4 − CD8 − thymocytes represent a developmentally unique subset in which both V δ and V β segments are nonrandomly expressed.