De Novo Expression of Receptors on T Cells

Abstract

The ability to effect selective and limited regulation of the vigor of the immune response is a potential therapeutic tool of almost unlimited promise. Since transition of T cells from the quiescent to the active state is a prerequisite for most immune functions, a detailed understanding of the T cell activation process is a logical first step toward achieving this goal of immunotherapy. Antigenic or mitogenic activation of lymphocytes initiates an ordered, complex sequences of entra- and intracellular events. Activated lymphocytes are phenotypically as well as functionally distinct from their progenitors (see Chap. 1). Cell surface antigens, often receptor proteins, that are induced to appear on T cells activated by the lectin phytohemagglutinin-P (PHA) can be classified both on the basis of the kinetics of their appearance and on their growth association properties. Seven distinct T cell activation antigens, defined by monoclonal antibodies (mAb), have been classified as early, intermediate, or late antigens based on their temporal appearance relative to DNA synthesis. Four antigens, the transferrin receptor, the T cell activation antigen Tac, the 4F2 antigen, and Tac antigen 49.9 are early antigens, whereas the OKT10 antigen appears at intermediate times, and both HLA-DR and antigen 19.2 appear late (Coiner et al. 1983). These findings are similar to the previously reported early expression of insulin-binding sites on activated lymphocytes (Heldermann and Strom 1979) and confirms the result of Uchiyama et al. (1981a) that Tac, the _p55 subunit of the interleukin 2 (IL-2) receptor, is expressed before DNA synthesis.