Inhibitory effect of heat-killed Lactobacillus strain on immunoglobulin E-mediated degranulation and late-phase immune reactions of mouse bone marrow-derived mast cells

This study investigated the in vitro effect of Lactobacillus strains, a major group of probiotic lactic acid bacteria, on immunoglobulin E (IgE)- and antigen-induced mast cell degranulation and subsequent gene expression. Bone marrow-derived mast cells (BMMCs) from DBA/2 mice were cultured with heat-killed Lactobacillus strains for 24 h. Some strains significantly inhibited IgE- and antigen-induced beta-hexosaminidase release from BMMCs. Furthermore, Lactobacillus reuteri NBRC 15892, which exhibited the strongest inhibitory activity, significantly reduced the elevated interleukin (IL)-4, IL-13, tumor necrosis factor-alpha, and cyclooxygenase-2 expression levels that was induced by 1-2 h of stimulation with IgE and antigens. The suppressive effect of NBRC 15892 strain on BMMC degranulation was significantly reduced in the presence of a toll-like receptor (TLR)2-neutralizing antibody. In addition, downregulation of cell surface Fc epsilon RI alpha expression was observed after 6 h of NBRC 15892 treatment. These results suggest that some Lactobacillus strains inhibited IgE-mediated mast cell degranulation and subsequent late-phase reactions involving mast cells via a TLR2-dependent mechanism with Fc epsilon RI alpha downregulation.