Localization of the enzyme neutral endopeptidase to the human synovium.

Abstract

Neuropeptides, contained within sensory nerve fibers in the synovium, are present in inflammatory joint fluids. The potency of these peptides in vitro has led to the hypothesis that enzyme degradation systems are operative in vivo. To address this question we localized neutral endopeptidase (NEP; EC 3.4.24.11) in human synovium. The normal human synovium failed to show any immunoreactivity for NEP. In the disease groups there was intense staining of cells surrounding blood vessels. Our data are consistent with the hypothesis that a proportion of synovial fibroblasts are the major source of this enzyme in the arthritic joint.