Exopolysaccharides from Lactobacillus rhamnosus RW-9595M stimulate TNF, IL-6 and IL-12 in human and mouse cultured immunocompetent cells, and IFN-γ in mouse splenocytes

Exopolysaccharides (EPS) from Lactobacillus rhamnosus RW-9595M have been prepared from bacterial cultures, isolated, concentrated, fractionated and tested in vitro for their possible modulating properties on mouse splenocytes from the C57Bl/6 and BALB/c strains, on the murine RAW 264.7 macrophage-like cell line and on human Peripheral Blood Mononuclear Cells (PBMC) from a total of 14 healthy donors. A first step of EPS fractionation was attempted, using membranes with different molecular weight cut-off. Fractions were as follows: F1: >1000 kg . mol -1 ; F2: 1000-100 kg . mol -1 ; F3: 100-10 kg . mol -1 ; F4: <10 kg . mol -1 . Total EPS, as well as F1, appeared slightly mitogenic in both mouse splenocytes and human PBMC in 2-3 d cultures, and F3 also exhibited such a property on human PBMC. Unfractionated concentrated ("total") EPS, as well as F1, elicited TNF, IL-6 and IL-12 p40 both in the mouse and human cells, in 6 h and 24 h cultures, with important variability depending on the cell source. In 24 h cultures, total EPS or F1 elicited bio-active IFN- in both C57Bl/6 and BALB/c splenocytes, and this IFN- secretion was sustained until at least 3 d of culture. In human PBMC, no IFN- production was observed despite high IL-12p40 secretion. These results suggest the possibility of enhancing the immune system through EPS from lactic acid bacteria, in individuals responsive to such a stimulus.