Dose-Dependent Effects of Lactobacillus rhamnosus on Serum Interleukin-17 Production and Intestinal T-Cell Responses in Pigs Challenged with Escherichia coli

ABSTRACT The mechanism underlying the dose effect of probiotics on ameliorating diarrhea has not been fully elucidated. Here, low (1 × 10 9 CFU/ml) or high (1 × 10 11 CFU/ml) doses of Lactobacillus rhamnosus ATCC 7469 were administered orally to piglets for 1 week before F4 (K88)-positive enterotoxigenic Escherichia coli (F4 + ETEC) challenge. Administration of a low, but not a high, dose of L. rhamnosus decreased the percentage of CD3 + CD4 + CD8 − T cells in the peripheral blood. Notably, transiently increased serum concentrations of interleukin-17A (IL-17A) were observed after F4 + ETEC challenge in pigs pretreated with a high dose of L. rhamnosus. Administration of L. rhamnosus increased the percentage of the small intestinal lamina propria CD3 + CD4 + CD8 − cells and Peyer9s patch CD3 + CD4 − CD8 − and CD3 − CD4 − CD8 + cells. The percentage of ileal intraepithelial CD3 + CD4 − CD8 + cells increased only in the high-dose piglets. Administration of L. rhamnosus downregulated expression of ileal IL-17A after F4 + ETEC challenge but had no effect on expression of gamma interferon (IFN-γ), IL-12, IL-4, and FOXP3 mRNA in the small intestine. Expression of jejunal IL-2, ileal transforming growth factor β1 (TGF-β1), and ileal IL-10 was upregulated in the low-dose piglets after F4 + ETEC challenge. Our findings suggest that amelioration of infectious diarrhea in piglets by L. rhamnosus is associated with the generation of lamina propria CD3 + CD4 + CD8 − T cells, the expansion of Peyer9s patch CD3 + CD4 − CD8 − and CD3 − CD4 − CD8 + cells, and the attenuation of F4 + ETEC-induced increase in CD3 + CD4 + CD8 + T cells in the small intestine. However, consumption of high doses of L. rhamnosus may increase levels of serum IL-17A after F4 + ETEC challenge, thus eliciting a strong proinflammatory response.