Modulation of the immune response by probiotic strains in a mouse model of gluten sensitivity (1)
Bacteria associated with probiotic activity have frequently been lactic acid bacteria (LAB) or bifidobacteria. Lactobacillus reuteri and Lactobacillus brevis were found to elicit Th1 cytokines IL-1b, IL-2 and TNF-a but not Th2 cytokines such as IL-10 and IL-4. IL-12 is considered a critical factor in switching naïve or memory T cells in Th1 responses that lead to vigorous immunity against infection and other diseases.
Wheat gliadin (100 mg) was resuspended in 1 ml of 0.1 M NH4HCO3 pH 7.9 and 2 M urea; a-chymotrypsin was added for 24 h at 37 °C; reaction was stopped by incubating in boiling water 10 min; urea was removed by column desalting; the chymotryptic digest of gliadin (ct-gliadin) was freeze-dried and stored at -20 °C. DQ8 mice were administered intragastrically with 500 ug of ct- gliadin along with 25 ug of cholera toxin (CT) on days 0, 7 and 14. LPS challenge induced the expression of CD86 but not of the co-stimulatory molecule CD80 and of the DC-specific marker CD11c.
Bacteria previously characterized for their probiotic properties were used.
The analysis of the cytokine pattern in iBMDCs revealed no significant difference for IL-12, whereas in mature (LPS-treated) BMDCs L. plantarum and L. fermentum enhanced its production. On the other hand, all the examined probiotic strains in- duced a significant increase of TNF-a in immature (B. lactis, L. plantarum, L. paracasei) and/or in mature (L. fermentum, B. lactis) DCs.
The treatment of ct-gliadin with CT induced a Th1-like immune response toward gliadin essentially characterized by IFN-g and TNF-a productions both in the systemic (spleen) and intestinal (MLN) compartments. Treatment with L. casei, used as positive control, specifically increased the antigen-specific IFN-g response both in spleen and in MLN.
Up-regulation of CD86 is consistent with other studies in which probiotic Lactobacillus species caused a similar enhancement. The constitutive expression of CD80 can play a role in gluten sensitivity of DQ8 tg mice. All strains were able to induce high levels of TNF- a in immature (B. lactis, L. plantarum, L. paracasei) or in mature (L. fermentum, B. lactis) DCs. TNF-a plays a pivotal role in inflammation, mediating fever and inducing the liver to produce various detrimental proteins. Tumor-suppressive activity of lactobacilli is thought to be due to the cytotoxic action of TNF-a and IL-1 produced by macrophages. If L. casei was administered in sensitized mice, an increase of the gliadin-specific cell-proliferation and IFN-g expression was found rather than tolerance induction.