Accessory molecules in T lymphocyte activation.

The currently accepted hypothesis used to explain the role of Lyt-2 and L3T4 in T cell activation proposes how these molecules interact with class I and II major histocompatibility complex molecules, respectively, on the antigen-presenting or target cell, to increase the avidity of binding of the antigen-specific T cell receptor. This has been tested using two antigen-specific, class II-restricted T cell clones expressing both Lyt- and L3T4. Inhibition of function was observed only with monoclonal antibody against L3T4, not Lyt-2. One interpretation of these results is that L3T4 and the class II-restricted T cell receptor can physically associate during T cell activation to form a multi-molecular complex from which Lyt-2 is excluded.