No abstract

In contrast to B cells or their antibody products, T lymphocytes have a dual specificity, for both the eliciting foreign antigen and for polymorphic determinants on cell surface glycoproteins encoded in the major histocompatibility complex (MHC restriction). The recent identification of T-cell receptor glycoproteins as well as the genes encoding T-cell receptor subunits will help to elucidate whether MHC proteins and foreign antigens are recognized by two T-cell receptors or by a single receptor. An important feature of MHC restriction is that it appears to be largely acquired by a differentiating T-cell population under the influence of MHC antigens expressed in the thymus, suggesting that precursor T cells are selected on the basis of their reactivity with MHC determinants expressed in the host thymus. To understand this process of 'thymus education', knowledge of the developmental regulation of T-cell receptor gene expression is necessary. Here we report that whereas messenger RNAs encoding the beta-and gamma-subunits are relatively abundant in immature thymocytes, alpha mRNA levels are very low. Interestingly, whereas alpha mRNA levels increase during further development and beta mRNA levels stay roughly constant, gamma mRNA falls to very low levels in mature T cells, suggesting a role for the gamma gene in T-cell differentiation.

Purified peripheral murine T cells, in the presence of concanavalin A, can be activated to produce interleukin 2 (IL-2) through stimulation either with a previously described murine lymphokine designated T cell-activating factor (TAF) or with a cloned human lymphokine that has been called P2 interferon, B-cell-stimulatory factor 2, hybridoma growth factor, inducible 26-kDa protein, or hematopoietic colony-stimulating factor 309 by different investigators. We and others propose the designation interleukin 6 (IL-6) for the latter molecule. Our experiments demonstrate that either murine TAF or human IL-6 can restore the ability of purified T cells to proliferate in response to Con A or antibodies against the T-cell antigen receptor. Most if not all of the proliferation can be blocked by antibodies against the a chain of the IL-2 receptor. Furthermore, highly purified CD8-T cells can be activated by IL-6 in the presence of Con A to secrete IL-2. We propose that IL-6 and murine TAF are important "second signals" in primary antigen-receptor-dependent T-cell activation. Whether or not murine TAF is a homologue of human IL-6 remains to be determined.The antigen-dependent pathway of T-cell proliferation appears to require engagement of the T-cell receptor complex by antigen associated with one of the major histocompatibility complex (MHC)-encoded glycoproteins (1)