Antigen-Specific T Cell Clones Restricted by DR, DRw53 (MT), or DP (SB) Class II HLA Molecules. Inhibition Studies with Monoclonal HLA-Specific Antibodies Erik Qvigstad, Gustav Gaudernack, and Erik Thorsby ABSTRACT: T lymphocyte clones (TLCs) specificfor Chlamydia trachomatis were obtained after lim- iting dilution of activated T cellsfrom a single donor, BS (HLA-A3; B7,15; DR1,4; DRw53; DPw4). Most of the proliferative TLCs obtained apparently used restriction elements on DR1 or DR4 molecules, expressed in the antigen-presenting cells (APC). The restriction pattern of two TLCs, however, closelyfollowed the DRw5 3 specificity, while one TLC seemed to be restricted by elements on DPw4 molecules. A panel of murine monoclonal antibodies (Mabs) was employed to further dissect the restriction specificities. The proliferative capacity of some of the TLCs was studied with and without Mabs directed against different HLA molecules, using non-T cells, monocytes, and peripheral blood dendritic cells as APC. Two Mabs, 7.2 and D-54, which seem to detect monomorphic determinants on HLA-DR, inhibited both DR- and DRw53-restricted TLCs. One Mab, 109d6 which reacts with DRw53 determinants, selectively inhibited the DRw53-restricted TLCs. The DP-restricted TLC was not inhibited significantly by any tested Mabs, including two Mabs with putative specificity for monomorphic determinants on the DP molecule. ABBREVIATIONS APC antigen-presenting cells PBM FCS fetal calf serum IL-2 Interleukin 2 TLC Mab monoclonal antibody peripheral blood mononuclear cells T lymphocyte clone INTRODUCTION Human T4 helper/amplifier cells corecognize antigenic epitopes together with restriction elements on class II HLA molecules in antigen-presenting cell (APC) membranes. In man, at least three different class II HLA molecules have been detected: DR, DQ (the new nomenclature from The 9th International Histo- compability Testing Workshop) (DC), and DP (SB). In addition, recent data presented at the 9th International Histocompatibility Testing Workshop indicate that DRw53 (MT3) is encoded by the second/3 chain of the DR locus, the DR 32 chain. The DR molecules appear to be analogous to the murine I-E molecules From The Laboratory of Transplantation Immunology, The National Hospital (Rikshospitalet), Oslo, Norway. Address requests for reprints to Erik Qvigstad, M.D., Laboratory of Transplantation Immunology, Rikshospitalet, Oslo 1, Norway. ReceivedNovember 16, 1983; accepted August 7, 1984. Human Immunology 11,207-217 (1984) © ElsevierSciencePublishingCo., Inc.. 1984 52 VanderbiltAve., New York, NY 10017 2O7 0198-8859/84/$3.00