Species cross-reactive membrane-associated urothelial differentiation antigen

An antigen, termed "urothelium membrane antigen" (UMA), confined to urothelium and most abundantly associated with the asymmetric unit membrane of the terminally differentiated luminal cells was identified with a monospecific (absorbed or affinity purified) rabbit antiserum obtained by immunization with membranes from normal bovine urothelium. A cross-species immunofluorescence-positive reaction was observed in normal bladder: Luminal urothelial membrane reacted most intensely. Underlying normal urothelial cells also showed a weaker cytoplasmic reaction. Specific luminal membrane labeling was confirmed by transmission and scanning electron microscopy. Specificity of the anti-UMA differed from the general epithelial reactivity obtained with antibodies to bovine urothelium cytosol. Anti-UMA did not cross-react with keratin, although there was some evidence of a filamentous localization in the cytoplasm of permeabilized cells. UMA was variably expressed by urothelial carcinoma-derived cell lines to a degree apparently related to the degree of cell differentiation, showing the highest positivity on the well-differentiated RT4 and RT112 lines and only a very weak reaction with the anaplastic MGHU-1 (EJ) and T24 lines. On immunoblots, anti-UMA reacted with a peptide of approximately 54,000 daltons.