INTRAPERITONEAL CULTIVATION OF SMALL-CELL CARCINOMA INDUCES EXPRESSION OF THE RETINAL CANCER-ASSOCIATED RETINOPATHY ANTIGEN

Objective: We have inquired into the reason why patients with cancer-a ssociated retinopathy (CAR) produce antibody reactions with the 23-kd retinal CAR antigen. Possible reasons include the expression of this a ntigen in the related carcinoma. Previous studies have failed to ident ify any antigenic counterpart expressed by in vitro cultivated small-c ell carcinoma of the lung. We, therefore, inquired into the effects of in vivo cultivation of the cancer cells and its influence on protein expression, with specific reference to the appearance of the 23-kd ret inal CAR antigen. Design: A complementary DNA library was prepared fro m small-cell carcinoma of the lung cells propagated intraperitoneally in Lewis rats and probed with antibodies reactive with the 23-kd retin al CAR antigen. Results: We found evidence of the expression of a canc er-associated gene in ascites-propagated small-cell carcinoma of the l ung that encodes for a protein antigenically similar to the 23-kd reti nal CAR antigen. A complementary DNA encoding this protein revealed co mplete DNA sequence homology with the retinal CAR antigen showing the cancer cells are expressing this photoreceptor protein. Conclusions: W e hypothesize that the carcinoma-retina immunologic cross-reaction is responsible for the induction of the unique antibody response encounte red in patients with CAR with vision loss developing as a cancer-evoke d autoimmune retinopathy.