Characterization of the target cell antigen in I region-mediated lympholysis.

Cytotoxic T lymphocytes (CL) can be produced by culturing I region disparate spleen cells as previously reported. More recently, it was shown that these CL can lyse other target cells which shared only the I-A subregion with the stimulator cells, i.e., lysis of these target cells is not H-2K/D restricted. Since I region-mediated lympholysis represents the only strong exception ruling out the obligatory role for H-2K/D products in mediating cytolysis of target cells, it is important to characterize further the target antigen recognized by CL in this system.A.TH anti-A.TL or (A.TL × B10.A) Fl anti-B10.HTT CL were generated in a 4-day primary culture system. The CL, shown to be Thy-1⁺, are able to kill targets that share only the central region of H-2 with the stimulator cells. These I region-specific CL can also lyse target cells that express a cross-reacting Ia antigen with the stimulator cells. Incompatibilities at IA/IB and IE/IC gave stronger cell-mediated lympholysis than incompatibilities at IA/IB only. Experiments involving the use of cold target competition, inhibition by specific anti-Ia serum, and target cells containing different proportions of Ia⁺ cells, strongly suggest that the target antigens recognized by the CL are in fact Ia antigens.