Influences of a fermented milk with Lactobacillus bulgaricus and Streptococcus thermophiles on gut associated lymphoid tissue, mucosal IgA, and gut flora in mice

Abstract

<h2>Summary</h2><h3>Background</h3> Various effects of fermented milks on the immune system have been reported. However, their effects on gut associated lymphoid tissue (GALT) remain controversial. We examined influences of a fermented milk with <i>Lactobacillus bulgaricus</i> and <i>Streptococcus thermophilus</i> on intestinal flora, GALT mass and mucosal IgA levels using uninjured and injured murine models. <h3>Methods</h3> Experiment 1: Mice were fed a fermented milk diet containing 20% fermented milk with <i>Lactobacillus bulgaricus</i> and <i>Streptococcus thermophilus</i> (FM group) or an unfermented milk diet (UFM group) for 7 days (Days 0–6) <i>ad libitum</i>. The mice were killed on Day 7, and lymphocyte numbers in Peyer patches (PP), intraepithelial spaces (IE), and the lamina propria (LP) were determined, as well as the phenotypes of these lymphocytes (B cells, CD4+ T cells, CD8+ T cells, αβTCR+ T cells, γδTCR+ T cells), and the mucosal IgA levels in nasal, bronchoalveolar, and intestinal washings. We also measured bacterial flora in the cecum. Experiment 2: Mice were fed the FM or the UFM diet for 7 days ad libitum. On Day 7, the mice underwent gut ischemia reperfusion (IR). On Day 8, the mice were killed, and the same parameters as in experiment 1 were measured. <h3>Results</h3> In experiment 1, the percentage of CD4+ T cells in the LP was significantly higher in the FM than in the UFM group. The percentage of bacteria of the order <i>Lactobacillales</i> in cecal contents was higher in the FM than in the UFM group, while the <i>Bacteroides</i> percentage of cecal contents was lower. In experiment 2, the phenotypic expressions of γδ+TCR cells in PP and IE lymphocytes were significantly lower in the FM-IR than in the UFM-IR group. <h3>Conclusion</h3> The fermented milk with <i>Lactobacillus bulgaricus</i> and <i>Streptococcus thermophilus</i> examined herein does not clearly exert beneficial effects on GALT lymphocyte cell numbers and mucosal IgA levels in mice regardless of gut flora modulation.