Systemic Immunity after Local Antigenic Stimulation of the Lymphoid Tissue of the Gastrointestinal Tract

Abstract

Abstract The distribution of antibody-producing cells (APC) in the lymphoid tissues of rabbits orally immunized to a low concentration of bovine serum albumin (BSA) was compared to that found in intravenously (i.v.) or subcutaneously (s.c.) immunized animals by determining the concentration of direct and indirect plaque-forming cells in the lymphoid tissues. The spleen was the major site of APC in the i.v. immunized animals and APC predominated in the peripheral lymph nodes of the s.c. immunized group. In contrast, a major site of APC in the orally immunized animals was not directly identified. The concentrations of APC in the spleens of the orally immunized animals were similar to those in the s.c. immunized group, and a relative absence of APC was found in the peripheral and mesenteric lymph nodes, appendix, and Peyer's patches from orally immunized animals. For determining if systemic immunity is acquired in orally immunized animals in the absence of antibody production by systemic lymphoid tissues, rabbits ingesting the antigen for several weeks were given 50 mg BSA i.v. and the concentrations of APC in the systemic lymphoid tissues were determined 3 days later. Plaque-forming cells were not detectable 3 days after an i.v. injection of BSA given to previously nonimmunized animals, although at this time a marked increase in their concentration was detected in the lymphoid tissues of the i.v. challenged-orally immunized animals. These studies provide additional evidence that after local antigenic stimulation at gastrointestinal mucosal surfaces, the major site of both secretory and circulating antibody production is the gut-associated lymphoid tissues and that the systemic lymphoid tissues acquire the capacity to produce anti-BSA.