To test the hypothesis of an active autocrine loop involving proNGF production and p75NTR expression in RA-FLS, we inhibited p75NTR using a neutralizing antibody or LM11A-31, a non-peptide ligand of p75NTR that selectively blocks the binding site of proNGF (44, 45). Here, NGFR is linked to rheumatoid arthritis.