Heat-Killed Lactobacillus plantarum KCTC 13314BP Enhances Phagocytic Activity and Immunomodulatory Effects via Activation of MAPK and STAT3 Pathways

Identification of novel probiotic strains is of great interest in the field of functional foods. Specific strains of heat-killed bacteria have been reported to exert immunomodulatory effects. Herein, we investigated the immune-stimulatory function of heat-killed Lactobacillus plantarum KCTC 13314BP (LBP). Treatment with LBP significantly increased the production of $TNF-{\alpha}$ and IL-6 by macrophages. More importantly, LBP was able to enhance the phagocytic activity of macrophages against bacterial particles. Activation of p38, JNK, ERK, $NF-{\kappa}B$, and STAT3 was involved in the immunomodulatory function of LBP. LBP treatment significantly increased production of $TNF-{\alpha}$ by bone marrow-derived macrophages and splenocytes, further confirming the immunostimulatory effect of LBP in primary immune cells. Interestingly, the immunomodulatory effects of LBP were much stronger than those of Lactobacillus rhamnosus GG, a well-known probiotic strain. These results indicate that LBP can be a promising immune-enhancing functional food agent.