High levels of the proNGF peptides LIP1 and LIP2 in the serum and synovial fluid of rheumatoid arthritis patients: evidence for two new cytokines.

The proNGF peptides LIP1 and LIP2 display multiple biological and physiological properties several of which share common features with the nerve growth factor (NGF). The objective of this study was firstly to demonstrate the presence of these peptides in the human sera and secondly to provide evidence for their involvement in inflammatory diseases. Their levels measured by specific enzyme-linked immunosorbent assays (ELISA) were found to be more than 10-fold higher in sera of patients with rheumatoid arthritis (RA), as compared to healthy controls. High levels of LIP1 and LIP2 were also detected in the synovial fluid (SF) of RA patients. These results provide first evidence for a cytokine-like role of the LIP1 and LIP2 peptides.