Effects of yogurt ingestion on mucosal and systemic cytokine gene expression in the mouse

To assess the potential for ingestion of yogurt to modulate immunity, its e ffects on basal gene expression of cytokines in systemic and mucosal sites were determined in mice. Yogurts were manufactured from pasteurized nonfat dry milk using five commercial starter cultures with or without Bifidobacte rium sp. and Lactobacillus acidophilus. Treatment mice were fed the AlN-93G diet mixed 1:1 with unheated yogurt or heat-treated yogurt (wt/wt) for 2 a nd 4 weeks, and control mice were fed the AIN-93G diet mixed 1:1 (wt/wt) wi th nonfat dry milli. The viability of the various bacterial groups in unhea ted yogurts was maintained above 10(6) CFU/g throughout the feeding period. The yogurt-feeding regimens did not significantly affect weight gain. Rela tive mRNA levels in spleen, mesenteric lymph nodes, or Peyer's patches for the cytokines interferon-gamma, tumor necrosis factor-alpha, interleukin-2, -4, and -6, and the "housekeeping gene" beta(2)-microglobulin were determi ned by reverse transcriptase-polymerase chain reaction in conjunction with hybridization analysis. Prolonged feeding of some yogurts decreased express ion of several cytokine mRNAs, the depression of tumor necrosis factor-alph a mRNA in the spleen being the most prominent effect. Heat-treated yogurts were more effective in altering cytokine mRNA expression than were unheated yogurts containing viable organisms. Generally, yogurts either had no effe ct or decreased specific cytokine mRNA in the test organs, regardless of wh ether they contained Bifidobacterium sp. and L. acidophilus. These results suggest that, in contrast with previous studies in vitro, some yogurt formu lations may reduce rather than stimulate basal cytokine expression and that these effects are most prominent in the systemic compartment.