Lymphoid chemokine B cell-attracting chemokine-1 (CXCL13) is expressed in germinal center of ectopic lymphoid follicles within the synovium of chronic arthritis patients

A unique feature in inflammatory tissue of rheumatoid arthritis (RA) is the formation of ectopic lymphoid aggregates with germinal center (GC)-like st ructures that can be considered to contribute to the pathogenesis of RA, be cause local production of the autoantibody, rheumatoid factor, is thought t o be a causative factor in tissue damage. However, the factors governing th e formation of GC in RA are presently unknown. To begin to address this, th e expression of B cell attracting chemokine (BCA-1) (CXCL13), a potent chem oattractant of B cells, was examined in the synovium of patients with RA or with osteoarthritis (OA), Expression of BCA-1 mRNA was detected in all RA samples, but in only one of five OA samples. Lymphoid follicles were observ ed in four of seven RA samples and in two of eight OA samples, and in most of them BCA-1 protein was detected in GC, BCA-1 was not detected in tissues lacking lymphoid follicles, Notably, BCA-1 was detected predominantly in f ollicular dendritic cells in GC. CD20-positive B cells were aggregated in r egions; of BCA-1 expression, but not T cells or macrophages, These data sug gest that BCA-1 produced by follicular dendritic cells may attract B cells and contribute to the formation of GC-like structures in chronic arthritis.