Supplementation with the probiotic Lactobacillus casei Shirota has no immunomodulatory effect in healthy men with a low baseline NK cell activity

Abstract

Probiotics have been shown to modulate the immune system. In healthy humans, however, contradictory results were observed. Thus, in a randomized double‐blind, placebo‐controlled trial the effect of the probiotic Lactobacillus casei Shirota (LcS; 1,95x1010 cfu/day) on immune functions of healthy men with low baseline NK cell activity (n=34/group) was investigated (study period 8 wk, i.e. a 2‐wk run‐in period, 4 wk supplementation and a‐2 wk follow‐up). Individuals of the control group (n=34) consumed the same drink manufactured without LcS. LcS had no effect on NK cell activity and immune cell phenotypes in peripheral blood mononuclear cells. Further, phagocytic activity and intensity of monocytes and neutrophils, oxidative burst, cytokine secretion pattern and saliva SIgA concentrations did not differ between groups. The incidence of potentially pathogenic microorganisms including S. aureus and hemolytic streptococci in the nasopharyngeal microflora was also not changed. In summary, under the present conditions supplementation with LcS caused no immunomodulation. However, other dosages of LcS might be effective as indicated by trials using higher LcS dosages. Dietary habits of study subjects may also be relevant for the outcome of the trial and may impede a demonstration of immunomodulatory activities of probiotics in open studies.The study was supported in part by a grant from Yakult Honsha CO., Ltd.