By Stefan

Using antigen-specific human T lymphocytes as immunogens, it has been possible to generate monoclonal antibodies against clonally unique surface determinants expressed on a novel class of 90-kdalton Ti molecules. Each surface Ti molecule exists as a heterodimer comprised of a covalently linked 49-kdalton aand 43-kdalton 0-chain and, in addition, is membrane-associated with the 20 / 25-kdalton T3 molecule (1-3). Perhaps more importantly, in contrast to the monomorphic T3 structure, differences in proteolytic cleavage and isoelectricfocusing analyses of Ti structures from clones of unrelated specificities suggest that peptide variability exists within the latter (2). Given the fact that monoclonal antibodies to the Ti structure of clones of unrelated specificities are non-cross-reactive and by themselves inhibit antigenspecific clonai function, it is likely that anti-Ti monoclonal antibodies define variable regions of the T cell antigen receptor (3). If such a notion were correct, then it might be anticipated that under the appropriate conditions, anti-Ti antibodies could induce clonal T cell activation in a fashion analogous to antigen. In the present study, this possibility was investigated by triggering T cell clones with purified anticlonotypic monoclonal antibodies coupled to the surface of a solid support (Sepharose 4B) and this mode of activation compared with that induced by cell surface bound antigen itself. In the results to be reported, we demonstrate that analogous to antigen, anticlonotypic monoclonal antibodies selectively induce clonal proliferation and lymphokine production.