Oral administration of Enterococcus faecalis FK-23 suppresses Th17 cell development and attenuates allergic airway responses in mice

Evidence is increasing that oral administration of probiotics can attenuate asthmatic responses both in murine models and clinical trials. T-helper 17 (Th17) cells, a subset of CD4(+) T cells have been implicated as having an important role in the development of several allergic disorders, but the relationship between oral administration of probiotics and Th17 development has not been well studied. BALB/c mice were given lysed Enterococcus faecalis FK-23 (LFK) orally for 28 days. After sensitization by subcutaneous injection of ovalbumin (OVA) on Days 14 and 21 and 1% OVA inhalation on Days 25,26 and 27, they were challenged with a 5% OVA aerosol on Day 28. Twenty-four hours later, airway resistance and accumulation of inflammatory cells in bronchoalveolar lavage fluid (BALF) and lung tissues were determined. Interleukin (IL)-17-expressing CD4(+) lymphocytes isolated from lung, spleen and lamina propria of the intestine were detected by flow cytometry. The expression of IL-6 and TGF-beta mRNA was assessed by real-time PCR. Increases in airway hyperresponsiveness, and numbers of total leukocytes and mast cells in BALF induced by OVA challenge were significantly suppressed by oral administration of LFK. The increased percentage of IL-17-expressing CD4(+) cells from lung, spleen and intestine in OVA-challenged mice was reduced following LFK treatment. We conclude that the oral administration of LFK suppresses the asthmatic response and that this is associated with attenuation of Th17 cell development.