[Studies on the induction of the humoral immune responses to Bacteroides gingivalis fimbrial antigen in mice].

Serum and salivary antibody responses to Bacteroides gingivalis fimbriae administered either orally or subcutaneously (s.c.) with or without an adjuvant in various strains of mice were examined in this study. Following results were obtained. 1) Oral administration of B. gingivalis fimbriae with GM-53 as an adjuvant in liposomes, but not in Tris-HCl buffer, definitely enhanced the fimbriae-specific IgG responses, mainly IgG1 followed by IgG2b, IgG2a and IgG3 in serum and IgA response in saliva of BALB/c mice. On the other hand, s.c. injection of fimbriae with GM-53 or MDP-Lys (L18) also raised the fimbriae-specific IgG followed by IgA and IgM responses in serum, and both IgA and IgG responses in saliva of BALB/c mice. Oral immunization was less effective than s.c. injection in terms of the production of serum antibody in the mice. However, the level of salivary antibody of mice injected s.c. was similar to that of mice immunized orally. 2) High anti-fimbriae antibodies in serum were maintained in BALB/c mice immunized orally with fimbriae and GM-53 in liposomes for approximately 7 months after the primary immunizations. Oral administration also induced and held the fimbriae-specific IgA response in saliva for at least 6 months after the primary immunizations. The levels of fimbriae-specific IgA in saliva after the second boosters on days 123 and 124 were higher than those after the primary ones on days 27 and 28. 3) Among various strains of mice immunized orally with fimbriae and GM-53 in liposomes, BALB/c and DBA/2 mice (H-2d) significantly produced high levels of both serum IgG and salivary IgA antibodies specific for fimbriae. Furthermore, B10.D2 mice (H-2d) were responders followed by B10.BR (H-2k), while C57BL/10 mice (B10, H-2b) were low responders to the fimbriae. These results show that the combined use of fimbriae together with an adjuvant results in a sharply increased IgA antibody response in saliva and a predominantly stimulated IgG antibody in serum, and it was suggested that these responses are restricted by H-2 haplotype.