CXCL13 and synovial sarcoma: In our previous study [24], the prevalence of ectopic germinal center (GC) formation along with CXC chemokine ligand-13 (CXCL13) was low in HTLV-I-seropositive patients with SS, especially in HAM patients with SS, indicating that the low prevalence of serology in the present study might be explained by a low prevalence of GCs and CXCL13, because CXCL13 in GCs is an important factor to attract B cells [25, 26] that differentiate into plasma cells and produce autoantibodies such as anti-SS-A/Ro antibody.