Lactobacillus rhamnosus GG and Streptococcus thermophilus induce suppressor of cytokine signalling 3 (SOCS3) gene expression directly and indirectly via interleukin-10 in human primary macrophages

Summary In the present study we have characterized T helper type 2 (Th2) (interleukin (IL)-10)/Th1 (IL-12) cytokine expression balance in human primary mac- rophages stimulated with multiple non-pathogenic Gram-positive bacteria used in the food industry and as probiotic substances. Bacteria representing Lactobacillus, Bifidobacterium, Lactococcus, Leuconostoc, Propionibacterium and Streptococcus species induced anti-inflammatory IL-10 production, although quantitative differences between the bacteria were observed.S. ther- mophilus was able to induce IL-12 production, while the production of IL-12 induced by other bacteria remained at a low level. The highest anti- inflammatory potential was seen with bifidobacteria, as evidenced by high IL-10/IL-12 induction ratios.All studied non-pathogenic bacteria were able to stimulate the expression of suppressor of cytokine signalling (SOCS) 3 that controls the expression of proinflammatory cytokine genes.Lactobacillus and Streptococcus species induced SOCS3 mRNA expression directly in the absence of protein synthesis and indirectly via bacteria-induced IL-10 pro- duction, as demonstrated by experiments with cycloheximide (CHX) and anti-IL-10 antibodies, respectively. The mitogen-activated protein kinase (MAPK) p38 signalling pathway played a key role in bacteria-induced SOCS3 gene expression. Enhanced IL-10 production and SOCS3 gene expression induced by live non-pathogenic Lactobacillus and Streptococcus is also likely to contribute to their immunoregulatory effects in vivo.