Local immunological response in the posterior intestinal segment of the rainbow trout after oral administration of macromolecules.

This paper deals with the effect of an orally administered antigen (human immunoglobulin G, IgGH) on the local intestinal immune system of trout kept at 12 degrees C. Significantly increased numbers of antigen-binding (ABC) and plaque forming cells (PFC) were induced in the epithelium by a single oral administration of antigen. In the primary immune response, ABC and PFC first occurred on days 4 and 6 respectively and peak counts were obtained at day 6 and 10 respectively. PFC counts returned to background levels by day 18. Lymphoid cells recovered from the intestinal epithelium 3 days after immunization were able to proliferate and to secrete Ig in vitro. 24 h after administration, the antigen could be visualized by immunofluorescence on the outer surface of the intraepithelial macrophages. An intestinal secretory immune system stimulated by oral administration of antigens is operative in trout, a carnivorous species with a well differentiated stomach.