CD19 and autoimmune disease: While previous studies have reported associations between tryptophan and autoimmune diseases via B cell immune responses, as well as between autoimmune diseases and Parabacteroides distasonis, this study identifies a correlation between the tryptophan synthesis gene K01696 (trpB) from Parabacteroides distasonis and B cell-specific genes (CD19, CD22, CD79B, and PTPN6).