Expression of RT1.A and RT1.B/D antigens on endothelium of rat kidneys

The presence of major histocompatibility complex (MHC)-encoded antigens (RT1) on endothelium of rat kidneys was investigated using hyperimmune allogeneic rat sera (HIS) in an indirect immunofluorescence technique with kidney sections. Endothelial antigens detected with anti-MHC sera segregated in an F2 generation with the RT1 antigens on erythrocytes. The MHC specificity of the endothelial staining was established with kidneys from congenic strains. The existence of public and private determinants on endothelium was shown by absorption experiments with spleen cells from several strains. RT1.A antigens were demonstrated on the endothelium of arteries, capillaries, and veins, using purified anti-RT1.A antibodies. This was confirmed using the MHC-recombinant PVG.1R strain. RT1.B/D antigens were found on the endothelium of capillaries and veins of the same strain. Furthermore, red blood cell-absorbed HIS, monoclonal anti-Ia antibodies, and mouse alloantisera which cross-react with rat Ia-like antigens were used. Based on this cross-reactivity, it appeared that I-E/C-like but not I-A-like antigens were detected on endothelium. RT1.C region antigens were not detected. Antisera against RT2, Ag-F, Ag-S, and immunoglobulin allotypes did not bind to normal kidneys. We conclude that RT1.A and some RT1.B/D specificities are expressed on rat renal endothelium.