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• T.spiralis infection could induce the production of Bregs in mice. • Bregs are an important source of spleen and MLN IL-10 in mice infected with T.spiralis. • IL-10 was mainly secreted by the CD19+CD1dhigh CD5+ B cell subset. • The Bregs phenotype is similar toT2-MZP cells after T.spiralis infection in mice. Regulatory B cells (Bregs), a subset of B lymphocytes discovered in the past few decades, have the capacity to suppress the immune response and dampen inflammation by secreting cytokines (IL-10 and TGF-β). Whether Bregs are involved in Trichinella spiralis infection and the phenotypic characteristics of these cells after infection are still unknown. We investigated the phenotype of and dynamic changes in IL-10-producing Bregs in Trichinella spiralis infection in BALB/c mice. We used multicolour fluorescence immunostaining of microwave-treated paraffin sections to investigate the number of Bregs in T. spiralis infection. Flow cytometry (FCM) was used to determine the frequency of Bregs and related subgroups and cytokines in the spleen and mesenteric lymph nodes (MLNs). High levels of IL-10 were detected in the spleen and MLNs of mice after infection with T. spiralis. Furthermore, the frequencies of IL-10-producing CD19+CD1dhighCD5+ regulatory B cells and CD19+ cells were increased during T. spiralis infection. We also showed that the induced phenotype was similar to that of transitional type 2 marginal zone precursor B cells (T-MZP) cells after T. spiralis infection in mice. This study is the first demonstration of the expansion of Bregs following T. spiralis infection. [ABSTRACT FROM AUTHOR]