Systemic and intestinal immunities after different typhoid vaccinations.

The comparative studies of systemic and intestinal immunities to S. typhi were performed in 29 healthy volunteers during 2 years after receiving oral vaccination with attenuated S. typhi Ty21a in gelatin capsule, parenteral vaccination with acetone inactivated or heat inactivated-phenol preserved S. typhi Ty2. The methods used were immunobead ELISA for total secretory IgA and indirect ELISA for specific secretory IgA in the intestinal lavage fluid. The specific systemic IgG, IgM and anti-O, anti-H agglutinins were measured by indirect ELISA and Widal test respectively. The leukocyte migration inhibition test was used for the measurement of systemic cell mediated immunity. The results indicate that the oral S. typhi Ty21a stimulated intestinal immunity better than both parenteral vaccines but evoked less systemic antibody response. The stimulation of systemic cell-mediated immunity by the live attenuated and acetone inactivated vaccine was comparable while stimulation by heat inactivated-phenol preserved vaccine was less pronounced. The same studies were performed in 26 healthy volunteers during 6 months following different doses of oral vaccination with S. typhi Ty21a in enteric-coated capsule. The results suggest that the stimulation of intestinal and systemic immunities by this vaccine is dosage dependent. Three doses of vaccine provide better stimulation than two doses and one dose, respectively.