These cells were first detected in the synovial fluid and tissue of patients with rheumatoid arthritis (RA) patients, and phenotypically resemble Tfh, in particular through the secretion of IL‐21, a central cytokine for B‐cell differentiation and CXCL13, a B‐cell chemoattractant [4]. The gene discussed is IL21; the disease is rheumatoid arthritis.