CD4 and immunoglobulin G4-related sclerosing disease: Both CD4+ CTLs and CD8+ CTLs, but not Th1 and Th2 cells, are significantly more abundant in the lesions of IgG4-RD, correlate with disease activity, and may contribute to the initiation of T cell-mediated apoptosis and tissue fibrosis in the disease-affected organs [29, 88].