Immune effects of probiotics

Abstract

Twenty papers concerning the effects on the immune system of ingestion of probiotic bacteria in humans have been reviewed. Several studies report that intake of probiotics stimulate cell-mediated immune effector functions. Thus, enhanced production of interferon-y by blood cells, enhanced phagocytosis by polymorphonuclear leukocytes (PMN) and to a lesser extent monocytes, and enhanced expression of complement receptors on PMNs are effects quite consistently seen in subjects consuming probiotic bacteria. It is likely that this is the result of probiotic bacteria being taken up across the small intestinal mucosa and being ingested by macrophages, leading to the production of cytokines and other mediators stimulating cell-mediated immunity. Probiotics have also been suggested to function as adjuvants, i.e. agents that increase immune responses to other antigens administered concomitantly. However, responses to vaccination are generally only mildly increased during probiotic consumption and most likely depend on the occurrence of cross-reactive antibodies that are induced by the probitic bacteria but also bind to structures on unrelated antigens. A few studies have tested the clinical effect of probiotics on allergy, but to date no effect has been convincingly proven. In conclusion, probiotic treatment could be beneficial in conditions where stimulation of cell-mediated effector functions is desired. Key words: clinical studies, humans, immune, probiotics