Induction of Mucosal and Serum Immune Responses to a Specific Antigen of Periodontal Bacteria

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Abstract
The dynamics of the host immune response to periodontal bacteria not only may be informative from the standpoint of specific mucosal protection to these pathogens, but also may reveal the capacity of the mucosal immune response to provide protection of the host. To this end, we have examined the immune response to chromatographically purified fimbriae of P. gingivalis administered orally or systemically with liposomes and adjuvant in BALB/c mice, high responders to this antigen. Oral administration of P. gingivalis fimbriae clearly enhanced the fimbriae-specific salivary IgA response. ELISPOT analysis revealed that significant numbers of fimbriae-specific IgA SFC were seen in lamina propria and mesenteric lymph nodes but not in Peyer's patches of mice immunized orally. In contrast, antigen-specific IgM and IgG SFC were seen mainly in the circulating blood mononuclear cells. On the other hand, subcutaneous injection of fimbriae with GM-53 also raised the fimbriae-specific IgG followed by IgM and IgA responses in serum, and both IgA and IgG responses in saliva. Oral immunization was less effective than subcutaneous injection in terms of the serum antibody response. However, the salivary antibody level of mice injected subcutaneously was similar to that of mice immunized orally. In the subcutaneously immunized mice, fimbriae-specific SFC were detected in the spleen, blood, and brachial lymph nodes by ELISPOT assay. Fimbriae-specific IgM SFC appeared earlier and antigen-specific IgG SFC were seen later. These results show that the combined use of fimbriae together with the adjuvant results in sharply increased IgA responses in saliva and IgG responses in serum. In summary, it is clear that the nature of the host's antibody response in serum and mucosal secretions is distinct, and depends on the route of antigen administration, the use of adjuvant and/or liposomes, and the temporal phase of the humoral immune response following various immunization regimes.