In interleukin-4-deficient mice, alum not only generates T helper 1 responses equivalent to Freund's complete adjuvant, but continues to induce T helper 2 cytokine production

The role of interleukin (IL)-4 in the activity of two frequently used vaccine adjuvants, Freund's complete adjuvant (FCA) and the aluminum hydroxide gels (alum), was studied using the standard antigen ovalbumin (OVA) in IL-4 genedisrupted mice (IL-4 -/-). In the absence of adjuvant, there was an overall reduction in antibody production to OVA in IL-4 -/- mice and significantly greater amounts of interferon (IFN)-gamma were produced following restimulation of splenocytes with antigen in vitro compared with immunocompetent controls (IL-4 +/+). FCA and alum boosted the immune response to OVA in both IL-4 -/- and IL-4 +/+ mice. In IL-4 +/+ mice, while FCA stimulated a wide-spectrum immunoglobulin response, including both Th1-associated IgG2a and Th2-associated IgG1, alum enhanced only Th2 antibody production and no OVA-specific IgG2a could be detected. In IL-4-deficient mice, however, not only was IgG2a production increased in all adjuvant-treated groups, but alum was as potent at stimulating this antibody subclass as FCA. Similarly, increased production in vitro by splenocytes of the Th1 cytokine IFN-gamma, equivalent to that produced after inoculation with FCA/OVA, was only detected in IL-4 -/- mice inoculated with alum/OVA. There was no IgE production in IL-4 -/- mice and OVA-specific IgG1 production, although still at significant levels, was reduced compared with wild-type mice irrespective of the adjuvant used. However, although production of the Th2 cytokine IL-5 was totally inhibited in IL-4-deficient mice inoculated with FCA/OVA, there was no significant difference in IL-5 production between the two strains when alum was used as adjuvant.