Antibody to rat collagen, prepared in rabbits and injected into the circulation of normal or adjuvant-prepared rats, becomes fixed to its antigen and can then be identified in tissue sections under ultraviolet light by its fluorescence after application of fluorescein-conjugated anti-rabbit globulin. In heart, lung, liver, spleen, adrenal, kidney, jejunum, lymph node, thymus, joint synovia, peripheral nerve, aorta, skeletal muscle, eye, and brain, the antibody was found at all sites where collagen and reticulin are normally present, but except for the kidneys of the adjuvant-prepared rats, no pathological abnormalities were demonstrated. It was not found within cells.
Specific fluorescence was absent from tissues of rats injected with normal rabbit serum or rabbit anti-fish collagen serum or rabbit anti-rat collagen serum after absorption with rat collagen, but was present when the anti-rat collagen serum had been absorbed with fish collagen. The reaction could be blocked by pretreatment of sections with unlabeled anti-rabbit globulin and did not occur with heterologous labeled anti-duck globulin.
After serial treatment in vitro with homologous antibody to collagen and the conjugated anti-rabbit globulin, purified reconstituted collagen fibers showed the same fluorescence as fibers in the tissues; no fluorescence of the fibers occurred when heterologous antibody to collagen was applied.
These findings indicate that the antibody to rat collagen is directed toward an antigen present in both collagen and reticulin.