Given the importance of the pDC-driven type I IFN response in both murine and human AIP/IgG4-RD, one might predict that T helper type 1 (Th1) and/or follicular helper T type 1 (Tfh1) cells are a dominant part of the T cell response and indeed enumeration of the various types of T cells found in lesional tissue associated with AIP/IgG4-RD shows that IFN-γ–producing T cells comprise a large fraction of the total T cell population present in such tissue (9, 15–17). Here, IFNG is linked to immunoglobulin G4-related sclerosing disease.