The response of gut-associated lymphoid tissue in gnotobiotic piglets to the presence of bacterial antigen in the alimentary tract.

The cellular changes in the ileum and duodenum and in the mesenteric and prefemoral lymph nodes of gnotobiotic piglets were observed following feeding with a live culture of a non-pathogenic E. coli. There was a rapid and intense reaction in the lower ileum, and follicles were formed; germinal centres were formed in the mesenteric lymph node after a short delay. Germinal centres were not seen in the prefemoral lymph node, though there were pyroninophilic cells in the cortex of this node. Plasma cells were not detected in the medulla of either the mesenteric or the prefemoral lymph nodes, but pyroninophilic cells and plasma cells were found in the lamina propria of the duodenum from 7 days after infection oneards. These observations demonstrate the requirement of an intestinal flora for the development of normal Peyer's patch architecture and indicate that the Peyer's patch response secondarily affects the mesenteric lymph node. The observations also suggest that there is a haematogenous dissemination of pyroninophilic cells from gut-associated lymphoid tissue to, amongst other sites, the duodenum; this may be of importance in both natural and artificial immunization by the oral route.