Immunomodulatory effects of lactic acid bacteria on human peripheral blood mononuclear cells

The aim of study was to evaluate the effect of a mixture of three strains (administered in vitro ) of lactic acid bacteria ( Lactobacillus acidophilus, Lactobacillus delbrueckii ssp. bulgaricus, Bifidobacterium bifidum ) designed as Trilac, representing a part of normal human microflora on: 1) human peripheral blood mononuclear cells (PBMC) proliferation, 2) profile of cytokine synthesis and 3) expression of monocyte and lymphocyte receptors, known to be involved in non-specific and specific immune responses. Trilac induced only a moderate proliferative response (about 10-20% of PHA-induced level) in PBMC. The CD4+ T cell was the responder subset. Trilac was a rather poor inducer of IFN-g and IL-12, simultaneously inducing relatively higher expression of IL-10 and TNF-a. Trilac also induced an increase in the expression of some monocyte surface receptors (CD14, IL-2R, HLA-DR, ICAM-1, CD80), simultaneously having only slight effect on the expression of lymphocyte surface receptors, as determined by double colour flow cytometry. We conclude that stimulation of PBMC with commensal lactic acid bacteria ongoing in Trilac resulted in a characteristic pattern of immune response manifested by: a) restriction of proinflammatory activities (IL-10 prevailed over IL-12 and IFN-g), b) significant activation of monocytes but rather slight T-cell induction. Hence, Trilac-induced immune activities may indicate its potential ability for limitation of pathogen-induced pro-inflammatory responses in microflora (via IL-10 action) and simultaneous induction of antimicrobial effect (via TNF-a induction and monocyte activation). Key words : lactic acid bacteria, lymphocytes, monocytes, cytokines, co-stimulatory receptors.