Differences in immune responses induced by oral and rectal immunizations with Salmonella typhi Ty21a: Evidence for compartmentalization within the common mucosal immune system in humans

Based on the concept of the common mucosal immune system, immunization at v arious inductive sites can induce an immune response at other, remote mucos al surfaces. The immune responses elicited through rectal and oral routes o f antigen delivery were compared with respect to (i) measurement of antibod y responses in serum and various external secretions of the vaccinees and ( ii) characterization of the nature and homing potentials of circulating ant ibody-secreting cells (ASC). Specific ASC appeared in the circulation in 4 of 5 volunteers after oral and 9 of 11 volunteers after rectal immunization with Salmonella typhi Ty21a. The kinetics, magnitude, and immunoglobulin i sotype distribution of the ASC responses were similar in the two groups. In both groups, almost all ASC (99 or 95% after oral or rectal immunization, respectively) expressed alpha 4 beta 7, the gut homing receptor (HR), where as L-selectin, the peripheral lymph node HR,was expressed only on 22 or 38% of ASC, respectively. Oral immunization elicited a more pronounced immune response in saliva and vaginal secretion, while rectal immunization was mor e potent in inducing a response in nasal secretion, rectum, and tears. No m ajor differences were found in the abilities of the two immunization routes to induce a response in serum or intestinal secretion. Thus, the rectal an tigen delivery should be considered as on alternative to the oral immunizat ion route. The different immune response profiles found in various secretio ns after oral versus rectal antigen administration provide evidence for a c ompartmentalization within the common mucosal immune system in humans.