Circulatory antigen of Heymann nephritis. III. Presence of the 70‐kD circulatory protein in the immune deposits of Heymann nephritis
An antigen of 70 kD size has been isolated previously from normal rat serum which has immunological cross‐reactivity to the Heymann nephritis antigen, F x 1 A. Its role in the pathogenesis of Heymann's nephritis was unknown. In this investigation we tested for the presence of 70‐kD circulatory antigen in the glomerular immune deposits of Heymann's nephritis. Further, its presence was correlated with severity of disease. It was observed that the presence of the 70‐kD antigen strongly correlated with the existence of electron‐dense deposits in the lamina rara externa (LRE) of the glomerular capillary wall and with pathologic proteinuria. Temporally, the presence of the 70‐kD antigen in the immune deposits was followed by large electron‐dense deposits, enhanced complement activity and proteinuria. The data suggest that in the growing immune complex lattice in the LRE. the 70‐kD circulatory antigen by virtue of its small size, mobility and antigen cross‐reactivity facilitates cross linking and coalescence of immune complexes, resulting in electron‐dense immune deposits (EDD) formation which initiates complement activation and consequent proteinuria.