Cloned human T cells synthesize Ia molecules and can function as antigen presenting cells.

TNP-specific proliferative cloned human T cell lines were investigated for their synthesis and cell surface expression of HLA-DR molecules and for their capacity to function as antigen presenting cells. Utilizing radioactive amino acid precursors for metabolic labeling, these studies demonstrated endogenous synthesis of HLA-DR molecules by cloned T cells, which by two-dimensional gel electrophoresis were similar to HLA-DR molecules expressed by B cells and monocytes. Moreover, when TNP-modified, the irradiated cloned T cells functioned very effectively to stimulate TNP-specific proliferation by cloned responders; when unmodified they were potent stimulators of allogeneic mixed leukocyte responses. Thus, for haptens covalently attached to cell membrane proteins and for allogeneic HLA antigens, Ia+ cloned T cells can function as effectively for antigen presentation and T cell activation as other Ia+ populations to which such properties have been ascribed.