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 1A. 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.