A human leukocyte antigen identified by a monoclonal antibody

Leukocyte antigen of approximate molecular weight 200,000 daltons have beendescribed in mouse, rat, and man. We described here the reactivities of a monoclonal antibody. GAP 8.3, which identified such an antigen on human leukocytes. We found the leukocyte antigen H-T200 on T and B lymphocytes, granulocytes, monocytes, and platelets, but not on erythrocytes or nonhematopoetically derived cells. Resting and activated T cells had more antigen or their surfaces than did resting B lymphocytes and EBV-transformed B cells, respectively. The leukocyte antigen was detected on approximately 75% of bone marrow cells; cells of the erythroid series comprised the negative population. The GAP 8.3 antibody and its F(ab′)₂ fragments had no effect on in vitro stimulation of peripheral blood cells by mitogens or allogeneic cells. Antigen isolated from T cell lines had a higher electrophoretic mobility than did antigen from B cell lines; antigen from the mycloid line U937 comigrated with that from B cell lines. In addition, we detected very small but reproducible differences in the electrophoretic mobility of the antigen on two T cell lines.     

Inhibition of anti-class I cytotoxicity by anti-class II monoclonal antibodies (MoAb). I. Blocking of bulk non-DR and non-DQ-directed cytotoxic T cells by MoAb against DR, DQ, and DP

We previously demonstrated that although human cytotoxic T lymphocytes (CTL) generated against a lymphoblastoid cell line (LCL) mutant that had lost DR and DQ (formerly known as MB) expression were directed primarily at class I antigens, the lytic activity of such CTL could be inhibited by monoclonal antibodies (MoAb) against monomorphic determinants on DR molecules. Furthermore, the inhibitory effect was found to occur by binding of the MoAb to the target cell, not the effector cell, because lysis of LCL target cells not expressing DR was not inhibited. In this paper we extend this phenomenon to show (i) that MoAbs directed against DQ and DP class II gene products also inhibit the lysis of LCL target cells by CTLs recognizing class I antigens; and (ii) that not all DR-specific MoAbs blocked target cell lysis by non-DR specific CTLs. In addition, when PBLs were used to stimulate the generation of CTLs in mixed leukocyte culture (MLC), inhibition using anti-class II (DR, DQ, and DP) MoAb occurred only when LCLs but not PHA blasts were used as targets. This might be explained by elevated expression of class II molecules on LCLs compared to PHA blasts.     

The avidity of cross-reactive virus-specific T cells for their viral and allogeneic epitopes is variable and depends on epitope expression

Virus-specific T cells can recognize allogeneic HLA (allo-HLA) through cross-reactivity of their T-cell receptor (TCR). In a transplantation setting, such allo-HLA cross-reactivity may contribute to harmful immune responses towards the allograft, provided that the cross-reactive T cells get sufficiently activated upon recognition of the allo-HLA. An important determinant of T-cell activation is TCR avidity, which to date, has remained largely unexplored for allo-HLA-cross-reactive virus-specific T cells.For this purpose, cold target inhibition assays were performed using allo-HLA-cross-reactive virus-specific memory CD8⁺ T-cell clones as responders, and syngeneic cells loaded with viral peptide and allogeneic cells as hot (radioactively-labeled) and cold (non-radioactively-labeled) targets. CD8 dependency of the T-cell responses was assessed using interferon γ (IFNγ) enzyme-linked immunosorbent assay (ELISA) in the presence and absence of CD8-blocking antibodies.At high viral-peptide loading concentrations, T-cell clones consistently demonstrated lower avidity for allogeneic versus viral epitopes, but at suboptimal concentrations the opposite was observed. In line, anti-viral reactivity was CD8 independent at high, but not at suboptimal viral-peptide-loading concentrations.The avidity of allo-HLA-cross-reactive virus-specific memory CD8⁺ T cells is therefore highly dependent on epitope expression, and as a consequence, can be both higher and lower for allogeneic versus viral targets under different (patho)physiological conditions.