Immunological regulation of Fenneropenaeus chinensis tropomyosin-stimulated sensitization by Bifidobacterium infantis in mice

Abstract:

[Objective] This work aims to compare the preventive and therapeutic effects of Bifidobacterium infantis 13.085 on suppression of shrimp tropomyosin (TM) sensitization in BALB/c mice. The balance of Treg/Th17 ratio and expression of Treg-and Th17-associated cytokines were also studied.[Methods] Shrimp tropomyosin was purified by ammonium sulfate and isoelectric precipitation. Four groups (Positive1, B. infantis therapy, Positive2 and B. infantis prevention) of BALB/c mice were immunized by intraperitoneal (IP) injection of purified TM together with incomplete Freund's adjuvant. Negative control animals received equal amounts of sterile PBS with Freund's adjuvant at each sensitization and challenge point. Allergic symptoms were evaluated by diarrhea, anaphylactic symptoms, HE staining analysis of lung tissue, changes of body weight and splenic viscera coefficient. The levels of specific IgE, IgG2a and histamine in sera were determined by ELISA. The amount of Treg and Th17 cell subsets were analyzed by flow cytometry. The mRNA expression levels of Treg-and Th17-associated cytokines and transcriptional factors were detected by quantitative PCR.[Results] The purity and yield of TM were 84.93% and 60.88%, respectively. In vivo study showed that B. infantis treatment ameliorated the development of diarrhea, anaphylactic symptoms and inflammation of lung tissue. The splenic viscera coefficient also decreased in B. infantis treatment groups compared to positive controls. At the end of experimental period (day 56), the levels of specific IgE and histamine (P<0.05) as well as IL-17A mRNA expression (P<0.01) significantly reduced, while the Treg/Th17 ratio remarkably increased (P<0.05) in B. infantis treatment groups compared to positive controls. The level of CD25 mRNA expression significantly enhanced (P<0.01) in B. infantis therapy group compared to Positive1. In addition, the levels of specific IgE and IL-17A mRNA expression in B. infantis therapy group were much lower than those in B. infantis prevention group (P<0.05), while the Treg/Th17 ratio and CD25 expression level were higher in B. infantis therapy group compared to B. infantis prevention group (P<0.05).[Conclusion] Therapeutic administration of B. infantis 13.085 can effectively alleviate TM-stimulated allergic inflammation and symptoms, which may attribute to the balance of Treg/Th17 ratio, increase of Treg-associated cytokines expression, inhibition of Treg-associated cytokines secretion, and thus leading to blockade of inflammatory antibodies and histamine release.