Splenic B Cells Accumulate and Adopt a Pro-Inflammatory Phenotype to Accelerate Fibrosis in a CCl₄-Induced Liver Fibrosis Model

The spleen plays a significant role in hepatic fibrosis progression. B cells are the main splenic lymphocytes, but their specific contributions and underlying mechanisms remain unclear. Hepatic fibrosis was induced in mice by intraperitoneal administration of carbon tetrachloride (CCl₄). Splenectomy or sham operation was performed during the fibrotic process. Hepatic fibrosis severity and the proportion of splenic B cells were assessed. Splenic B cells isolated from fibrotic and control mice underwent mRNA sequencing. Protein expression of phosphorylated-p38 MAPK (p-p38 MAPK), total p38 MAPK, phosphorylated-NF-κB p65 (p-NF-κB p65), and total NF-κB p65 were determined by Western blotting using total protein extracted from the splenic B cells. Signal transduction pathways were investigated in isolated splenic B cells to elucidate mechanisms of phenotypic alteration. CCl₄-induced hepatic fibrosis was associated with B-cell accumulation in both the liver and spleen. Compared with the splenectomized mice, sham-operated fibrotic mice exhibited a higher proportion of hepatic B cells and more severe liver fibrosis. Splenic B cells from fibrotic mice showed an expansion of the IL-6-producing subset and elevated expression of pro-inflammatory cytokines. Moreover, splenectomy reduced the proportion of B cells within the fibrotic liver. Splenic B cells from fibrotic mice displayed upregulated expression of p-p38 MAPK and p-NF-κB p65. In CCl₄-induced hepatic fibrosis, splenic B cells accumulate and adopt a pro-inflammatory phenotype. This shift, mediated through activation of the p38 MAPK/NF-κB signaling pathway, promotes hepatic fibrosis progression. These findings identify splenic B cells as potential therapeutic targets for managing liver disease.