Evaluation of Immunomodulatory Activities of the Heat-Killed Probiotic Strain Lactobacillus casei IMAU60214 on Macrophages In Vitro

Abstract

Most <i>Lactobacillus</i> species have beneficial immunological ("immunoprobiotic") effects in the host. However, it is unclear how probiotic bacteria regulate immune responses. The present study investigated the effects of heat-killed <i>Lactobacillus casei</i> IMAU60214 on the activity of human monocyte-derived macrophages (MDMs). Human MDMs were treated with heat-killed <i>L. casei</i> at a ratio (bacteria/MDM) of 50:1, 100:1, 250:1, and 500:1, and then evaluated for the following: NO production, by Griess reaction; phagocytosis of FITC-labeled <i>Staphylococcus aureus</i> particles; cytokine secretion profile (tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-12p70, IL-10, and transforming growth factor (TGF)-β) by ELISA; and costimulatory molecule (CD80 and CD86) surface expression, by flow cytometry. Heat-killed <i>L. casei</i> IMAU60214 enhanced phagocytosis, NO production, cytokine release, and surface expression of CD80 and CD86 in a dose-dependent manner. All products were previously suppressed by pretreatment with a Toll-like receptor 2 (TLR2)-neutralizing antibody. Overall, our findings suggest that this probiotic strain promotes an M1-like pro-inflammatory phenotype through the TLR2 signaling pathway. These effects on macrophage phenotype help explain the probiotic efficacy of <i>Lactobacillus</i> and provide important information for the selection of therapeutic targets and treatments compatible with the immunological characteristics of this probiotic strain.