Study of the possible mechanisms involved in the mucosal immune system activation by lactic acid bacteria

The induction of a mucosal immune response is not easy due to the developme nt of oral tolerance, but under some conditions, bacteria can activate this immune system. Antigens administered orally can interact with M cells of P eyer's patches or bind to the epithelial cells. We have demonstrated that c ertain lactic acid bacteria are able to induce specific secretory immunity, and others will enhance the gut inflammatory immune response. The aim of t his work was to establish the reason for these different behaviors and to d efine possible mechanisms involved in the interaction of lactic acid bacter ia at the intestinal level. We studied IgA(+) and IgM(+) B cells comparativ ely in bronchus and intestine and CD4(+) T cells and IgA anti-lactic acid b acteria antibodies in the intestinal fluid, induced by oral administration of Lactobacillus casei, Lb. delbrueckii ssp. bulgaricus, Lb. acidophilus, L b. plantarum, Lb. rhamnosus, Lactococcus lactis, and Streptococcus salivari us ssp. thermophilus. The increase in the IgA+ B cells in the bronchus mean s that these lactic acid bacteria were able to induce the IgA cycle by inte raction with M cells from Peyer's patches or intestinal epithelial cells. T he IgM(+) cells increased when the stimulus did not induce the switch from IgM(+) to IgA(+). The increase in the CD4(+) cells suggests interaction of Peyer's patches and enhancement of the B- and T-cell migration. The anti-la ctic acid bacteria antibody is related to the processing and presentation o f the microorganisms to the immune cells. We demonstrated that Lb. casei an d Lb. plantarum were able to interact with Peyer's patch cells and showed a n increase in IgA(+), CD4+ cells, and antibodies specific for the stimulati ng strain. Lactobacillus acidophilus induced gut mucosal activation by inte raction with the epithelial cells without increase in the immune cells asso ciated with the bronchus. Although Lb. rhamnosus and Strep. salivarius ssp. thermophilus interact with epithelial cells, they also induced an immune r esponse against their epitopes. Lactococcus Lactis and Lb. delbrueckii ssp. bulgaricus induced an increase of IgA(+) cells entering the IgA cycle but not CD4(+) cells; thus, these bacteria would have been bound to epithelial cells that activated B lymphocytes without processing and presenting of the ir epitopes. We did not determine specific antibodies against Lc. lactis or Lb, bulgaricus.