An adjuvant formulation that preferentially induces T helper cell type 1 cytokine and CD8+ cytotoxic responses is associated with up-regulation of IL-12 and suppression of IL-10 production

Adjuvant preparations of Non-ionic surfactant vesicles (NISV) were compared, where appropriate, with Alum and Freund's complete adjuvant (FCA) for their ability to stimulate humoral and classical cell-mediated immune responses to a standard antigen, ovalbumin (OVA), and cell-mediated responses to a known T-cell epitope in BALB/c mice. Although NISV were able to induce antigen-specific, interferon-γ (IFN-γ) dependent, immunoglobulin G2a (IgG2a) production, the antibody response using Alum as adjuvant consisted entirely of the IgG1 isotype. Although OVA-specific lymphocyte proliferation in vitro was similarly enhanced by the use of Alum or NISV as adjuvant, cytokines detected in the culture supernatants were markedly different. Whereas production of the T helper cell 2 (Th2)-associated cytokine, interleukin-5 (IL-5), was significantly enhanced when Alum was used, the Th1-associated cytokine, IL-2, was primarily produced when NISVs were used as adjuvants. The use of this adjuvant also enhanced cytotoxic T-cell responses to OVA. Significant T-cell proliferation could also be generated against a synthetic peptide containing a T-cell epitope derived from the amino acid sequence of measles fusion protein when NISVs were used as adjuvant, but not FCA (Freund's Complete Adjuvant). In fact, over a range of antigen concentrations, greater stimulation indices were produced using NISV rather than FCA as adjuvant. Similarly, greater (though not significantly greater) quantities of the Th1-associated cytokine IFN-γ, were produced by antigen-stimulated lymphocytes when NISVs were used compared with FCA as adjuvant. Ex vivo studies of IL-12 and IL-10 production indicated that following administration of NISV, splenocytes were primed for increased IL-12 production, whereas IL-10 production was down regulated. We conclude that NISVs are effective adjuvants capable of stimulating Th1 and cytotoxic T-cell responses against protein and synthetic peptide antigens. Our results also suggest that this activity is associated with the ability of NISV to modulate IL-10 and IL-12 production to favor generation of Th1-type immune responses.