Co-ordinate expression of the pre-T-cell receptor complex and a novel immature thymocyte-specific antigen, IMT-1, during thymocyte development

Previously we described a monoclonal antibody (mAb) that reacted with a cel l-surface antigen, immature thymocyte antigen-1 (IMT-1), which is expressed on thymocytes of late CD4(-) CD8(-) (double negative) to early CD4(+) CD8( +) (double positive) differentiation stages. In this study, we investigated the expression of IMT-1 on various cell lineages in thymus as well as in p eripheral lymphoid organs. We found that IMT-1 is expressed on T-cell recep tor (TCR)-beta(lo) and TCR-delta(lo) thymocytes, but not on TCR-beta(hi), T CR-delta(hi) or natural killer (NK) 1.1(+) thymocytes, or on peripheral alp ha beta or gamma delta T cells. We also investigated the kinetics of expres sion of IMT-1 during fetal thymocyte development and compared it with the e xpression of the pre-TCR complex, comprising CD3, pre-TCR-alpha (pT alpha) and TCR-beta. We found that expression of both was similar, starting at day 14.5 of gestation, peaking on day 16.5 and gradually decreasing thereafter . Furthermore, the expression of both IMT-1 and pT alpha was drastically re duced when DN thymocytes in recombination activating gene (RAG)-2(-/-) mice were challenged in vivo with anti-CD3 mAb. These results indicate that IMT -1 is expressed on not only immature thymocytes of crp T-cell lineage but a lso on those of gamma delta T-cell lineage, and that the expression of IMT- 1 and the pre-TCR complex is co-ordinately regulated during the alpha beta lineage thymocyte development.