Suppressive Effects of Oral Administration of Heat-Killed <i>Lactobacillus acidophilus</i> on T Helper-17 Immune Responses in a Bovine β-Lactoglobulin-Sensitized Mice Model

The present study was planned to explore the effect of Lactobacillus (L.) acidophilus on the T helper-17 (Th17) immune response in a mouse model of β-lactoglobulin (β-lg) allergy. Bovine β-lg sensitised BALB/c mice were orally administered with different doses of heat-killed L. acidophilus (low, 5×10(7) colony forming unit (CFU); medium, 5×10(8) CFU; high, 5×10(9) CFU) in 200 µL of phosphate buffered saline (PBS) three times a week, starting from 1 week before β-lg sensitisation for 4 weeks. After the allergen challenge, the numbers of blood eosinophils and neutrophils were examined by light microscope; the levels of cytokine (interleukin (IL)-12, IL-4, tumor growth factor (TGF)-β, IL-10, IL-6 and IL-17A), total immunoglobulin E (IgE) and β-lg-specific IgE contents in the serum were measured with enzyme-linked immunosorbent assay (ELISA); The mRNA expression levels of TGF-β, IL-17A,CD25, Foxp3, retinoic acid-related orphan receptor γt (RORγt) and IL-10 were analyzed using real-time polymerase chain reaction (PCR). The results showed that oral administration of L. acidophilus suppressed hypersensitivity responses, attenuated the numbers of inflammatory cells and inhibited IgE production. We found up-regulation of TGF-β and down-regulation of IL-17A in the serum of L. acidophilus-treated group, along with IL-6 levels was significantly decreased than that of the allergy group (p<0.05). Moreover, the mRNA expression levels of CD25, forkhead box P3 and TGF-β were significantly higher in the spleen of L. acidophilus-treated group, while the mRNA expression levels of IL-17A, RORγt and IL-10 were significantly lower than that in the allergy group (p<0.05). In conclusion, the suppression of major allergic symptoms by oral administration of L.acidophilus was probably due to improve the regulatory T (Treg)/Th17 balance and inhibit the IL-6 production.