Characterization of kidney cell-specific, non-major histocompatibility complex alloantigen using antibodies eluted from rejected human renal allografts.

Previous studies from our laboratories (1) have indicated that eluates prepared from rejected kidneys have antibodies not only reactive to MHC class I and class II antigens but also to antigens unique for monocytes, endothelial cells, and kidney cells. To further define the serological and biochemical nature of antigens detected by the antibodies eluted from rejected kidneys, 13 eluates prepared from rejected renal allografts and two eluates from normal kidneys were absorbed with pooled platelets, normal splenic leukocytes and/or B cells from chronic lymphocytic leukemia patients. All of the eluates failed to react with normal T and B lymphocytes by microcytotoxicity and immunofluorescence assays. However, the eluates from rejected kidneys, but not normal kidneys, reacted with peripheral blood monocytes, endothelial cells cultured from umbilical cord as well as primary kidney cells. Detailed immunohistochemical analysis of frozen kidney sections showed that the eluates from rejected kidneys reacted with structures of the cortex while sparing the structures in the medullary region. All eluates bound to the glomerulus with intense fluorescence, but not to the mesangium and Bowman's capsule, while binding to interstitial capillaries, venous endothelium, and tubular epithelium varied. More significantly, none of the eluates reacted with frozen sections of the liver, spleen, or lymph node including the endothelial lining of blood vessels in these organs. Thus, the data indicate that the eluates prepared from rejected kidneys are recognizing organ-specific antigens expressed on the kidney cells. To identify the alloantigen(s) recognized by the eluted antibodies, an immunoblot analysis was performed against phase separated membrane proteins isolated from cortical kidney cells solubilized in 2X precondensed Triton X-114. A protein of Mr. 90,000-100,000 was identified as the target non-MHC antigen to which the eluates prepared from rejected allografts were reactive. Furthermore, our results suggest a possible polymorphism among these antigens.