To investigate correlations between serum IL-6 and clinical manifestations at the time of IgG4-RD onset, 43 patients with IgG4-RD were divided into two groups using a reference value of IL-6: a ≤ 4.0 pg/mL group (n = 33), and a > 4.0 pg/mL group (n = 10) (Table 4). Here, IL6 is linked to immunoglobulin G4-related sclerosing disease.