The percentage of these cells is positively correlated with other clinical parameters, including serum IgG4 levels and the number of involved organs in IgG4-RD patients, indicating the possible involvement of Tfr cells in IgG4-specific class-switch recombination in lesions of IgG4-RD [40, 79]. The gene discussed is TFRC; the disease is immunoglobulin G4-related sclerosing disease.