Antigenic Stimulation

Lymph nodes, spleens, and Peyer's patches of germ-free mice are relatively inactive. The tissues are small and contain rare, small, indistinct, germinal zones. When exposed to antigenic stimuli (Salmonella paratyphi A and lymphocytic choriomeningitis virus), the tissues become larger and germinal zones appear coincident with antibodies in the blood. The Peyer's patches were activated if antigen was absorbed from the intestinal lumen into the circulation but not if the antigen was administered parenterally. There was no demonstrable immunological response by the germ-free mouse to Streptococcus faecalis.