Secretory immunity induced in catfish, Ictalurus punctatus, following bath immunization

Individual adult channel catfish were immunized by immersion in an antigen bath containing dinitrophenylated-horse serum albumin. Anti-DNP hemagglutination titers of serum and cutaneous mucus were determined following both primary and secondary bath immunization. The results showed that five of the six fish had a cutaneous mucosal anti-DNP titer following the bath immunizations. In contrast, only one of the six catfish was shown to have any demonstrable change in its serum anti-DNP titer following the bath immunizations. The mucous anti-DNP hemagglutinin was shown to be antibody (Ab). The affinity-purified mucous Ab was found to have the same complex tetrameric architecture as well as the same molecular weight heavy and light chains as serum anti-DNP Ab. Histological studies showed that the catfish epidermis was richly vascularized. Within the epidermis there were numerous lymphocytes which were predominantly associated with the basal layer. These studies indicate that the secretory immune system of catfish can be stimulated by external antigens. Secondly, these studies show that bath immunization can differentially effect the relative antibody response of the catfish secretory and systemic immune systems.