Effect of parenteral immunization on the intestinal immune response to Salmonella typhi Ty21a as measured using...

The effects of parenteral administration of a killed typhoid vaccine on the intestinal immune response to live orally administered Salmonella typhi Ty21a in human subjects was assessed using an assay of in vitro specific antibody production by circulating peripheral blood lymphocytes (PBL). Previous priming with the parenterally administered vaccine had no effect on secondary immune responses to a live oral vaccine in humans with this response not differing in magnitude or duration from that following the primary oral vaccination course (p = 0.38). Following the primary PBL anti-LPS IgA response to an oral course of live vaccine in all subjects (6/6), boosting with a single oral dose of live vaccine resulted in 0/6 responders, while 2/11 subjects responded after a single dose of parenteral vaccine. No additional responses were evident after the second parenterally administered booster dose. PBL IgG and IgM responses were also demonstrated following oral vaccination, with 1/6 and 2/6 subjects parenterally vaccinated demonstrating IgM PBL responses after the first and second vaccination respectively. This study confirmed that parenteral vaccination did not impair the PBL IgA immune response to a secondary course of live orally administered organisms, and that multiple parenteral booster doses did not induce primary or secondary recirculation of antigen-specific PBL.