Long-term immunological memory induced by recombinant oral Salmonella vaccine vectors

We have previously shown that Salmonella enterica serovar Typhimurium expre ssing the hagB hemagglutinin gene from Porphyromonas gingivalis can induce primary and recall immune responses in serum and secretions in mice; howeve r, the longevity of memory induced by oral Salmonella carriers has not been adequately demonstrated. In this study, we examined the capacity of mice t o mount a recall response 52 weeks after primary immunization. Recall respo nses were seen in serum immunoglobulin G (IgG) and IgA following boosting a t week 52, and in most cases, they were equal to or greater than the primar y responses. Significant mucosal IgA recall responses in saliva and vaginal wash were also detected following boosting at week 52, In addition, there was a considerable residual response in secretions at week 51, prior to boo sting. These results indicate that oral Salmonella vectors can induce long- term memory to recombinant HagB and are particularly effective at inducing long-lasting mucosal responses as well as at inducing the capacity for muco sal recall responses.