MAST CELLS AND NEUROPEPTIDES IN HUMAN ELBOW JOINT CAPSULES

Abstract

The hypothesis is that mast cell numbers and neuropeptide containing nerve fibres are increased in the elbow joint anterior capsule of patients with post-traumatic contractures when compared to normal capsules.

Capsules were obtained from two patients with chronic contractures following radial head fractures and two organ donor elbows free of contractures. Four sections from each capsule were double-labelled with specific antibodies to the mast cell marker chymase and the neuropeptide calcitonin gene-related peptide (CGRP). Species specific secondary fluorescent antibodies were used to detect the marker antibodies and cells were identified with a fluorescent nuclear marker (DAPI). Images were captured using a microscope (200x magnification) and five randomly selected areas were sampled for each section obtained from all joint capsules. Chymase positive cell numbers and numbers of nerve fibers (minimum length fifty micrometres) were gathered.

The number of chymase positive mast cells was 6x greater in the contracture capsules when compared to normal capsules. In the contracture capsule, chymase positive mast cells represented 39% of total cells while in control capsules they represented 7% of total cells. Total cell numbers were similar in the capsules of both groups. The number of CGRP positive nerve fibres was increased 3x in the contracture capsule when compared to normal capsule.

Mast cell numbers and neuropeptide positive fibre numbers are increased in the elbow joint anterior capsule of patients with post-traumatic contractures when compared to normal tissues. Neuropeptides such as CGRP can induce mast cell degranulation. Mast cells release profibrotic molecules such as transforming growth factor beta1 (TGF-b1), a myofibroblast upregulator. It has been described that TGF-b1 and myofibroblast numbers are elevated in human elbow joint capsules in post-traumatic contractures. While these trends are encouraging, more subjects are needed to determine whether the mast cell and neuropeptide nerve fibre findings can be generalised to larger numbers. If future work supports a myofibroblast - mast cell - neuropeptide - fibrosis axis in the joint capsule in post-traumatic contractures, then methods to modulate this axis, such as mast cell stabilisers, may be evaluated in animal models.