We hypothesize that IFN-γ, produced by activated Th1 cells or CD4+ (GZMA+) cytotoxic T lymphocytes, which are also abundant in AIP/IgG4-RD tissues and exacerbate fibro-inflammatory responses, may be a primary inducer of CXCL9 [14, 51, 52]. Here, CD4 is linked to immunoglobulin G4-related sclerosing disease.