Further studies on immunomodulatory effects of exopolysaccharide isolated from Lactobacillus rhamnosus KL37C

Abstract

Lactobacilli, bacteria of human microbiome and major probiotic bacteria, show immunoregulatory properties. The immunomodulatory effect can be achieved not only by whole bacteria but also by cellwall components such as peptidoglycan and lipoteichoic acid (LTA). Other, biological active bacterial products are exopolysaccharides (EPS), major components of the lactobacilli biofilm. The aim of this study was to examine immunostimulatory potential of highly purified EPS derived from L. rhamnosus KL37 (EPS37). We have examined the effect of EPS37 on some selected biological functions of major inflammatory cells (neutrophils, macrophages, dendritic cells) in vitro, and on OVA-specific humoral response in mice. We have shown weak antioxidant properties of EPS 37. It decreased the reactive oxygen species (ROS) production in neutrophils stimulated with zymosan, but had no effect on phagocytosis of dextran by macrophages. Interestingly, in contrast to LTA, pure EPS37 did not stimulate cytokine production by MΦ. Moreover, EPS37 did not induce synthesis of prostaglandin E2 (PGE2) and did not affect the expression of COX-2 protein in MΦ, while it slightly induced the production of IL-12p40 and of IL-6 but not IL-10, in dendritic cells. On the other hand, we have found that EPS37 diminished the production of OVA-specific IgG antibodies. Moreover, EPS37 inhibited the adjuvant effect of LPS. Therefore, our present results confirm the suppressor effect of EPS37 on antigen-specific humoral response in mice. These data extend our knowledge about the role of EPS in interaction between bacteria and the immune system. However, further studies are necessary to explain its role as a major component of biofilm matrix.