Evidence for a cutaneous secretory immune system in rainbow trout (Salmo gairdneri)

Serum and mucus of untreated rainbow trout did not contain detectable agglutinating antibody to sheep red blood cells. Intraperitoneal injections of sheep erythrocytes resulted in production of specific antibody in both serum and mucus. Immuno-diffusion and absorption studies confirmed that mucus and serum antibodies are antigenically similar. Indirect fluorescent antibody techniques demonstrated the presence of immunoglobulin-containing plasma cells in cutaneous dermis and mucus, supporting the hypothesis that an independent mammalian-like secretory immune system is operative in fish.