Propionic acid regulates immune tolerant properties in B Cells

Interleukin 10 (IL-10)-producing B cells (B10 cells) are a canonical cell fraction for regulating other activities of immune cells. Posttranscriptional modification of IL-10 in B10 cells is not yet fully understood. Short-chain fatty acids play an important role to regulate the functions of immune cells. This study aims to clarify the role of propionic acid (PA), a short-chain fatty acid, in regulating the expression of IL-10 in B10 cells. Blood samples were collected from patients with food allergy (FA) and healthy subjects. Serum and cellular components were prepared with the samples, and analysed by enzyme-linked immunosorbent assay and flow cytometry, respectively. The results showed that serum PA levels were lower in FA patients. PA concentrations were negatively correlated with serum cytokine Th2 concentrations, specific IgE concentrations in serum and skin prick test results. The peripheral frequency of B10 cells and the production of IL-10 in B cells were also associated with serum PA concentrations. Activation of B cells by CpG induced the production of IL-10 and tristetretrprolin (TTP), in which TTP caused the spontaneous decay of IL-10 mRNA. PA was necessary to stabilize the IL-10 mRNA in B cells by inducing the production of granzyme B, which resulted in the degradation of the IL-10 mRNA. Administration of PA attenuated FA response in mice by maintaining homeostasis of B10 cells. In conclusion, PA is needed to stabilize the expression of IL-10 in B10 cells. PA administration can mitigate experimental FA by maintaining B10 cell functions.