EFFECTS OF LACTOBACILLUS SPP. ON CYTOKINE PRODUCTION BY RAW-264.7 MACROPHAGE AND EL-4 THYMOMA CELL-LINES

We have hypothesized that lactobacilli used in fermented dairy product s can stimulate immune function via enhancing cytokine secretion by le ukocytes. To test the effects of lactobacilli on cytokine production, RAW 264.7 cells (macrophage model) and EL4.IL-2 thymoma cells (T helpe r cell model) were cultured in the presence of 16 representative strai ns of heat-killed Lactobacillus spp. cells. In unstimulated RAW 264.7 cells, most lactobacilli, when present at concentrations from 10(6) to 10(8) bacterial cells per ml, induced marked tumor necrosis factor al pha (TNF-alpha) production (up to 411-fold) compared to the negligible TNF-alpha in controls. A strain-dependent increase in interleukin 6 ( IL-6) production (up to 88-fold) was also observed without stimulation at concentrations of 10(8) bacteria per mi. Upon concurrent stimulati on of RAW 264.7 cells with lipopolysaccharide, bath IL-6 and TNF-alpha production were enhanced between 4.2- and 10.6-fold and 1.8- and 8.7- fold, respectively, when cultured with 10(8) lactobacilli per mi. In u nstimulated EL4.IL-2 cells, lactobacilli had no effect on interleukin 2 (IL-2) or interleukin 5 (IL-5) production. Upon stimulation of EL4.I L-2 cells with phorbol 12-myristate-13-acetate, IL-2 secretion increas ed up to 1.9-fold in the presence of 10(6) L. bulgaricus Lr 79 cells p er ml whereas this cytokine decreased in the presence of 10(7) or 10(8 ) lactobacilli per ml. In contrast, IL-5 secretion increased in the pr esence of increasing concentrations of lactobacilli (up to 3.1-fold wi th 10(8) L. bulgaricus NCK 231 cells per ml). The results indicated th at direct interaction of most lactobacilli with macrophages resulted i n a concentration-dependent enhancement of cytokine production, wherea s the effects on cytokine production by the T-cell model were smaller and strain dependent. The in vitro approaches employed here should be useful in further characterization of the effects of lactobacilli an t he gut and systemic immune systems.