Studies on the adjuvant activity of non-ionic surfactant vesicles: adjuvant-driven IgG2a production independent of MHC control.

The ability of non-ionic surfactant vesicles (NISV) to stimulate humoral responses to bovine serum albumin (BSA) in H-2b, H-2d and H-2k congenic mice on the Balb genetic background was compared with that of Freund's complete adjuvant (FCA). After two subcutaneous inoculations of BSA formulated in each adjuvant, the NISV preparation was found to stimulate significantly higher total antibody production than FCA in mice carrying the H-2b haplotype at all time points measured after secondary inoculation (2, 5 and 10 weeks) and in Balb/c mice (H-2d) at two weeks after inoculation. Both adjuvants were found to overcome the apparent non-responsiveness of Balb/B mice (H-2b) to BSA alone. Analysis of the IgG subclass responses to BSA revealed a pattern of IgG1 but not IgG2a production similar to that for whole immunoglobulin. IgG1 responses invariably differed significantly, not only between adjuvant formulations but also between different H-2 haplotypes receiving the same inoculation. On the other hand, IgG2a responses did not differ significantly between H-2 haplotypes in animals given the same adjuvant preparations, although they did differ significantly in mice given BSA alone. Therefore, these results suggest that adjuvants cannot only circumvent antigen-specific non-responsiveness or low responsiveness, but also can induce antibody isotype switching independent of major histocompatibility complex controls.