IL4 and infection: Following an infection, the immune system is activated, leading to the activation of a large number of lymphocytes that release cytokines such as interleukin (IL)-4, IL-6, IL-10, IL-13, and transforming growth factor-β.[8–10] This results in an abnormal immune response, leading to characteristic organ fibrosis and plasma cell infiltration.[11] IgG4-RD is generally characterized by plasma cell infiltration in affected organs, elevated serum IgG4 levels, and chronic fibrosis, but its clinical manifestations are diverse, often leading to misdiagnosis as infections or tumors.