Systemic and Mucosal Immune Responses in Mice after Mucosal Immunization with Group B Streptococcus Type III Capsular Polysaccharide-Cholera Toxin B Subunit Conjugate Vaccine

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Abstract
Group B streptococci (GBS) colonize the female genital and rectal tracts and can cause invasive infection in susceptible newborns. An optimally effective GBS vaccine should induce mucosal and systemic immunity. In this study, we investigate the local and systemic immune responses to GBS type III capsular polysaccharide (CPS) after mucosal vaccination of mice via intranasal, peroral, rectal, and vaginal routes, with GBS type III CPS conjugated with recombinant cholera toxin B subunit (GBS III CPS-rCTB). Cholera toxin (CT) was added as an adjuvant. Immunoglobulin G (IgG) and IgA antibodies to the CPS were tested in serum, lungs, and intestinal, rectal, and vaginal extracts by enzyme-linked immunosorbent assay. The conjugated CPS administered by intranasal, peroral, rectal, and vaginal routes was much more effective at inducing both mucosal and systemic antibody responses to GBS III CPS than was unconjugated CPS. The CPS-specific immune responses in various organs were dependent on the route of immunization. Generally, the highest levels of IgA and IgG were generated in the regions or sites of the conjugate exposure. Thus, intranasal vaccination elicited the highest anti-CPS IgA and IgG antibody levels in the lungs, whereas peroral administration in the intestinal site and vaginal vaccination elicited the highest antibody levels in the vagina. Rectal vaccination was superior to the other routes in inducing high antibody levels in the rectum. The four routes of mucosal vaccination also induced distant antibody responses to CPS. Rectal vaccination induced high specific IgA levels in the vagina and intestine, and oral administration induced high specific IgA levels in the lungs and rectum. All four routes of vaccination with the conjugate elicited similarly high levels of anti-CPS IgG in serum. Intranasal vaccination with different doses of the conjugate (10, 30, and 80 μg of CPS) did not have a significant influence on the anti-CPS specific antibody responses. Intranasal immunization induced better antibody responses when one dose of the conjugate was divided and given on three consecutive days compared to administration of the full dose on one occasion. In conclusion, rectal and vaginal vaccination may be the best way of stimulating anti-CPS immune responses in the rectal and vaginal tracts, while high levels of anti-CPS antibodies in the lungs can be achieved after intranasal administration. The vaccination regimen thus might influence the mucosal immune response to CPS. This conjugate may serve as an effective mucosal vaccine for preventing mucosal colonization and invasive infection caused by GBS.

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