Regular consumption of fermented foods containing lactic acid bacteria, such as yoghurt has been found to have a beneficial effect on immune function. In human studies, yoghurt intake has been shown to stimulate the response of systemic natural killer cells when presented with their targets and enhance phagocytic activity of monocytes. In other studies, the stimulation of immune function by probiotic bacteria and classical yoghurt starter cultures has been demonstrated.
Under normal conditions, most ingested bacteria are not able to cross the mucosal barrier of the gut; hence it is not immediately obvious how yoghurt starters and probiotic strains exert their systemic immunomodulatory effects. Cytokines, which act as mediators between the different cells of the immune system and are produced only in response to a stimulus, have been implicated as mediators of these effects. Supporting this theory is the fact that lactic acid bacteria have been shown to enhance the production of several cytokines by human peripheral blood mononuclear cells in vitro. However, evidence of a direct effect of yoghurt on cytokines production in vivo would help clarify their role.
A study by Meyer et al. investigated the effects of a daily intake of probiotic yoghurt on cytokine production in young healthy women, as compared with those of conventional yoghurt. Both yoghurts contained Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, while the probiotic yoghurt also contained additional L. casei DN 114 001. The stimulated production of tumour necrosis factor-α increased significantly for both yoghurts, a rise of 63% and 24% for the probiotic yoghurt and conventional yoghurt, respectively. Significant increases in the production of interleukin-1β and interferon-γ occurred with consumption of conventional and the probiotic yoghurt, respectively; the latter also decreased production of interleukin-10. No significant differences in cytokine responses were found between the two types of yoghurt, with both enhancing the stimulated production of proinflammatory cytokines.
Meyer, AL; Elmadfa, I; Herbacek, I; Micksche, M (2007). Probiotic, as well as conventional yogurt, can enhance the stimulated production of proinflammatory cytokines. Journal of Human Nutrition and Diet 20 (6) 590-598. View Abstract
