APICAL EXPRESSION OF AN ANTIGEN COMMON TO RABBIT YOLK-SAC ENDODERM AND KIDNEY PROXIMAL TUBULE EPITHELIUM

The tissue distribution, molecular weight, and biochemical nature of an antigen detected by a mouse monoclonal antibody designated 283D3 and raised against rabbit visceral yolk sac endodermal cells, has been investigated. The antigen is located on the luminal side of apical tubules and large sub-apical vesicles in rabbit yolk sac endoderm and proximal kidney tubule epithelial cells. It is expressed in a similar polarised fashion in epithelial cells lining the epididymis. Western blotting showed the antigen to comprise proteins of molecular weight 330-380 kDa. The antigen has been affinity purified from yolk sac and kidney and is predominantly protein in nature with a small percentage of N-linked carbohydrate. In terms of tissue distribution and molecular weight it has close similarity to Heymann nephritis antigen but differs in not being confined to coated pits. Its function is not known, but the association with endocytic elements implies a possible role in non-specific protein absorption.