The relationships between mRNA expression levels of IL-33 and Th2 cytokines (IL-4, IL-13) in SGs were examined, and the mRNA expression of IL-33 was positively correlated with Th2 cytokines in SGs from patients with IgG4-RD but not with Th2 cytokines in SGs from patients with SS and controls (Fig. 1B). Here, IL33 is linked to synovial sarcoma.