Effect of pre-existing immunity for systemic and mucosal immune responses to intranasal immunization with group B Streptococcus type III capsular polysaccharide-cholera toxin B subunit conjugate

The effects of priming with a group B Streptococcus type III capsular polys accharide (GBS CPS III)-recombinant cholera toxin B subunit (rCTB) conjugat e, purified GBS CPS III or rCTB alone on the systemic and mucosal immune re sponses to CPS III after intranasal (i.n.) immunization were investigated i n mice. Priming with purified GBS CPS III followed by boosting with GBS CPS III-rCTB conjugate or priming with the conjugate followed by boosting with foe CPS induced comparable levels of specific IgG and IgA in both serum an d in lungs and vagina. However, i.n. immunization comprising both priming a nd boosting with conjugate was superior to priming with CPS and boosting wi th conjugate or the reverse, especially with regard to inducing mucosal IgA anti-CPS responses. All the immunization schemes, except priming and boost ing with free CPS, induced high and similar levels of IgG1 in serum. In con trast, mice primed with free CPS III and then boosted with CPS III-rCTB con jugate by the i.n. route failed to produce significant levels of IgG2a, IgG 2b and IgG3 in serum, at difference from mice primed with the conjugate and boosted with either conjugate or free CPS. Pre-immunization with rCTB eith er i.n. or i.p. did nut suppress specific serum IgG responses induced by GB S CPS III-rCTB conjugate intranasally, but did inhibit serum and especially mucosal IgA responses. Our findings suggest that priming with CPS affects the distribution of IgG subclasses to GBS CPS and that pre-existing anti-ca rrier rCTB immunity can have an inhibitory effect on mucosal immune respons es elicited by the conjugate vaccine given by the i.n. route. (C) 2001 Else vier Science Ltd. All rights reserved.