Peptide containing nerves in human synovium: immunohistochemical evidence for decreased innervation in rheumatoid arthritis.

The innervation of normal and rheumatoid human synovium was studied by immunofluorescence microscopy. Antibodies against the general neuronal marker protein gene product (PGP) 9.5 and specific neuropeptides were used. We observed sensory nerves containing substance P (SP) and calcitonin gene related peptide (CGRP) as well as autonomic sympathetic fibers immunoreactive for neuropeptide tyrosine (NPY), its C terminal peptide (C-PON) and the catecholamine synthesizing enzyme tyrosine hydroxylase (TH). Three subpopulations of nerve fibers labelled with SP and CGRP were identified: some stained for SP or CGRP only and others contained both peptides. NPY/C-PON and TH labelled predominantly perivascular nerves. Quantification of immunostained nerves revealed a significantly decreased innervation of rheumatoid synovia. The densities of both PGP 9.5 and neuropeptide containing nerves were lower in all rheumatoid samples. Our results are compatible with a local release of neuropeptides into joint fluid and point to a disturbed neuronal control of rheumatoid synovial tissue.