Clostridium leptum induces the generation of interleukin-10+ regulatory B cells to alleviate airway inflammation in asthma

Asthma is one of the most common chronic inflammatory diseases of the respiratory tract. Previous studies have shown that the reduction of regulatory B cells (Bregs) can increase inflammation of the body and promote the formation of chronic airway inflammation in asthma, but the detailed mechanisms have not been fully elucidated. The intestinal flora Clostridium leptum (CL) has been reported to modulate immune regulatory cells in the body, but the specific mechanisms are not clear. This study aimed to investigate the effects of CL on the differentiation of interleukin (IL)− 10⁺ Bregs and the regulation of the asthmatic inflammation-associated immune network. The abundances of CL and the frequencies of blood Bregs from asthmatic patients and healthy controls were compared. The house dust mite (HDM)-induced asthma model was established in mice. The effects of CL exposure and B cell infusion on Breg differentiation, T cell cytokine production, and inflammatory cell infiltration in mouse lungs were examined. Bregs were cocultured with regulatory T cells (Tregs) and CD4⁺ non-Tregs to evaluate their roles on Foxp3 expression and T cell differentiation, respectively. Compared with healthy controls, asthmatic patients had significantly reduced frequencies of blood Bregs and abundances of fecal CL, and these two parameters were positively correlated. In the asthma model, the frequencies of Bregs in lungs were significantly reduced; while the infusion of Bregs isolated from CL- supplemented mice significantly reduced airway inflammation and hyperresponsiveness. In addition, Bregs inhibited the differentiation of cocultured non-Tregs into multiple effector cells and enhanced Foxp3 expression in cocultured Tregs. Bregs contribute to the alleviation of airway inflammation, which provides insight on implementing CL-based microbial induction of Bregs in asthma therapy.