CD4 and systemic lupus erythematosus: Recently, Tfh cells that were differentially defined as CD4+CXCR5+ICOShigh or PD-1highTfh cells or CD4+CXCR5+CD45RA− or CD4+CXCR5+CD45RA−PD-1+Tfh cells were all significantly expanded and contributed to the production of autoantibodies in autoimmune diseases such as AITD, RA, SLE, and IgG4-related diseases (IgG4-RD) [20, 21, 27–30].