Can immunoregulatory lactic acid bacteria be used as dietary supplements to limit allergies?

Studies in gnotobiotic animals have suggested that the intestinal bacterial flora may play an important role in priming the immune system during ontogeny to limit dysfunctional responses, including allergy. Prospective clinical studies have identified a higher incidence of allergy expression in early childhood among children who have low enteric populations of lactic acid bacteria (LAB), such as lactobacilli and bifidobacteria, further supporting a role for gut-colonizing bacteria in regulating immunological atopy. There is some evidence to suggest that supplementing the human diet with probiotic LAB might combat both allergy development and expression of atopy in allergy sufferers; however, definitive information, in the form of controlled intervention trials, remains scant. Recent immunological evidence has indicated that certain strains of LAB can stimulate the production of type I and II interferons and pro-interferon monokines (IL-12 and IL-18), following contact with the immune system; therefore, probiotic forms of immunoregulatory LAB could be used as dietary supplements to modify the gut microflora and provide pro-T helper cell 1 (Th1) STAT-activating signals sufficient to deviate the immune phenotype and correct the Th2-type bias which promotes allergy. This review outlines the clinical and laboratory evidence of a role for LAB in combating allergies, and attempts to explain this phenomenon in terms of our current understanding of immunoregulatory signals produced by gut-colonizing microbes.