Identification of human vascular endothelial cell/monocyte antigenic system using monoclonal antibodies

Recent studies have suggested that non-major-histocompatibility-encoded antigens expressed preferentially on vascular endothelial cells and/or monocytes may act as immunogens leading to allograft rejection. In order to further characterize the antigens and to investigate the roles of interleukins in the induction of such antigens, three murine monoclonal antibodies (SK2H10, SK3A1, SK2F11) were produced against interferon-γ-induced human umbilical vein endothelial cells. All three monoclonal antibodies reacted specifically with human endothelial cells cultured from umbilical veins as well as blood monocytes. Several human established cell lines with B, T, and erythroid/myeloid cell properties, as well as cell lines expressing HLA-class I and II antigens (SB, REH, HSB, K562 and HL-60) failed to react with these reagents, indicating that the binding structures on the endothelial/monocyte cell surface are distinct from HLA class I and II antigens. Furthermore, the binding characteristics of the three antibodies to endothelial cells, monocytes, and human monocytic cell line, U937, suggest that they recognize different determinants on the cell surface. Analysis of Ia-positive and Ia-negative clones of U937 demonstrated that the antibodies reacted strongly with the Ia-positive cell lines. The monoclonal SK2H10 reacted preferentially with phorbol esters-induced HL-60 and K562 cell lines; thus indicating that the antigens detected on the monocytes are associated with differentiation. The results indicate that these monoclonal antibodies to endothelial cells have specificities similar to those described for alloantisera defining the vascular endothelial cell/monocyte antigenic system and should facilitate definition of the biochemical and molecular nature of such antigens.