Gut immunology in fish: a review.

During recent years considerable study has been made of the systemic immune system of fish, although less attention has been paid to local immunity at sites such as the gut, reproductive tract and skin. Recent work on the structure of gut-associated lymphoid tissue and other intestinal cell populations, the absorption of macromolecules from the intestinal lumen and the production of specific mucosal antibodies strongly suggests, however, that the gut of these lower vertebrates is immunocompetent. This review briefly deals with current concepts on the nature of gut-associated lymphoid tissues and other cell populations in the gut, intestinal and biliary immunoglobulin (Ig), antigen uptake and the significance of oral vaccination in the protection of commercially reared fish against infectious disease.