With the increasing incidence of metabolic syndromes, more attention should be paid to the role of the C5a-C5aR1 pathway in inflammatory reactions and chronic diseases (such as autoimmune diseases, malignant tumors, and rheumatoid arthritis), especially the dose effect of double-edged C5a-C5aR1 pathway regulation. This evidence concerns the gene C5AR1 and autoimmune disease.