Despite the absence of direct data showing the induction of TLSs by Tph cells, the following findings collectively indicate that Tph cells play a crucial role in TLS induction: (i) ectopic CXCL13 is sufficient for TLS formation (37); (ii) scRNA-seq showing that Tph cells are the main source cells for CXCL13 (36); and (iii) RA synovial fluid mononuclear cells showed CXCL13-dependent lymphocyte migration ex vivo (5). The gene discussed is TPH1; the disease is rheumatoid arthritis.