LACTOBACILLUS-CASEI INHIBITS ANTIGEN-INDUCED IGE SECRETION THROUGH REGULATION OF CYTOKINE PRODUCTION IN MURINE SPLENOCYTE CULTURES

Background: Lactobacillus casei is a nonpathogenic gram-positive bacte rium widely used in dairy products and has been shown to enhance the c ellular immunity of the host. Methods: To examine the inhibitory effec t of L. casei on IgE production, splenocytes obtained from ovalbumin ( OVA)-primed BALB/c mice were restimulated in vitro with the same antig en in the presence of heat-killed L. casei. The effect of this bacteri um on T helper (Th) phenotype development was also examined with naive T cells from OVA-specific T cell receptor-transgenic mice. Results: L . casei induced IFN-gamma, but inhibited IL-4 and IL-5 secretion, and markedly suppressed total and antigen-specific IgE secretion by OVA-st imulated splenocytes. The inhibitory effect of L. casei on IgE, IL-4, and IL-5 production was partially abrogated by addition of neutralizin g antibody to IFN-gamma. Augmented IL-12 production was also observed in the cell cultures containing L. casei, and anti-IL-12 monoclonal an tibody completely restored the IgE, IL-4, and IL-5 production to the c ontrol levels. The IL-12 augmentation by L. casei was macrophage-depen dent. The Th cell development assay showed the ability of L. casei to induce Th1 development preferentially. This effect was also completely blocked by anti-IL-12 antibody. Conclusions: This is the first demons tration that a nonpathogenic microorganism, L. casei, can inhibit anti gen-induced IgE production through induction of IL-12 secretion by mac rophages. The findings suggest a potential use of this organism in pre venting IgE-mediated allergy.