PDCD1 and rheumatoid arthritis: c-Maf can promote the expression of IL-21, and IL-21 can directly regulate the proliferation and differentiation of B cells by binding to IL-21R in B cells.190,233,234 Tph cells can promote B-cell differentiation and antibody production in rheumatoid arthritis and SLE, but few studies have been conducted in AIH.235,236 Renand et al237 found that PD-1+CXCR5−CD4+ T cells were enriched in PBMCs of patients with active AIH or remission and that activation of humoral immunity and antibody production in AIH mainly depended on CD45RA−CD27+PD-1+CXCR5−CD4+ T cells but not on PD-1+CXCR5+CD4+ T cells.