Pertussis toxin can replace T cell receptor signals that induce positive selection of CD8 T cells

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Abstract
CD4+ helper T lymphocytes and CD8+ killer T lymphocytes are both generated in the thymus from common precursor cells expressing CD4 and CD8. The development of immature CD4+ CD8+ thymocytes into mature ‘single‐positive’ T cells requires T cell antigen‐receptor (TCR)‐mediated positive selection signals. Although it is known that the recognition specificity of TCR expressed by CD4+ CD8+ thymocytes determines their fate to become either CD4+ or CD8+ T cells, the molecular signals that direct precursor thymocytes to become CD4+ and CD8+ T cells are unclear. By using ZAP‐70− mutant thymus organ cultures in which T cell development is arrested at the CD4+ CD8+ thymocyte stage, the present study shows that distinct biochemical treatments can selectively restore the generation of mature CD4+ and CD8+ T cells, bypassing TCR‐induced positive selection signals. The combination of phorbol ester and ionomycin selectively restores the generation of CD4+CD8− TCRhigh cells consistent with previous results. On the other hand, we find that the generation of CD4− CD8+ TCRhigh cells is selectively induced by pertussis toxin. Interestingly, the signals generated by pertussis toxin, which increase Notch expression, can dominate the signals by phorbol ester and ionomycin, steering thymocyte development to CD8 lineage. These results indicate that distinct biochemical signals replace TCR signals that selectively induce positive selection of CD4+ and CD8+ T cells, and that biochemical treatment can manipulate the development and choice of CD4+ and CD8+ T cells.