Differential cytokine production in clonal macrophage and T-cell lines cultured with bifidobacteria

When used in commercial fermented dairy products, bifidobacteria may enhance immunity by stimulating cytokine secretion by leukocytes. To assess whether interaction between bifidobacteria and leukocytes promote cytokine production, we cultured RAW 264.7 cells (macrophage model) and EL-4.IL-2 thymoma cells (helper T-cell model) in the presence of 14 representative strains of heat-killed bifidobacteria. In unstimulated RAW 264.7 cells, all bifidobacteria induced pronounced increases (up to several hundred-fold) in the production of tumor necrosis factor-alpha compared with that of controls. Interleukin-6 production by unstimulated cells also increased significantly, but less than did tumor necrosis factor-alpha. Upon concurrent stimulation of RAW 264.7 cells with lipopolysaccharide, production of tumor necrosis factor-alpha and interleukin-6 were both enhanced between 1.5- to 5.8-fold and 4.7- to 7.9-fold, respectively, when cultured with 10(8) bifidobacteria/ml. In unstimulated EL-4.IL-2 cells, bifidobacteria had no effect on the production of interleukin-2 or interleukin-5. Upon stimulation of EL-4.IL-2 with phorbol-12-myristate-13-acetate, there were variable increases in interleukin-2 secretion (up to 2.4-fold for 10(6) Bifidobacterium Bf-1/ml) and interleukin-5 secretion (up to 4.6-fold for 10(8) B. adolescentis M101-4). The results indicated that, even when variations among strains were considered, direct interaction of most bifidobacteria with macrophages enhanced cytokine production, but the effects on cytokine production by the T-cell model were less marked. Interestingly, the 4 bifidobacteria strains used commercially for dairy foods showed the greatest capacity for cytokine stimulation. The in vitro approaches employed here should be useful in future characterization of the effects of bifidobacteria on gastrointestinal and systemic immunity.