TPH1 and immunoglobulin G4-related sclerosing disease: An increase in circulating Tph cells has also been observed in other autoimmune and inflammatory diseases, such as Sjögren’s syndrome,32 IgG4-related diseases (IgG4-RDs),33,34 systemic sclerosis,35 IgA nephropathy36 and type I diabetes.37 Some correlations were observed between the frequency of circulating Tph cells and disease activity and/or clinical parameters in these diseases.