Marked expression of TNF receptors in human peritendinous tissues including in nerve fascicles with axonal damage - Studies on tendinopathy and tennis elbow.

The peritendinous connective tissues can have importance in chronic tendon pain. Recently cytokine TNF-α has been suggested to be involved in tendinopathic processes. It is not known how TNF-α and its receptors TNFR1 and TNFR2 are expressed in peritendinous tissues. The objective for this study was to immunohistochemically evaluate the expression patterns of these in the peritendinous tissue located between the plantaris and Achilles tendons and the one located superficially to the extensor origin at the elbow region for patients with tendinopathy/tennis elbow. The nerve fascicles were of two types, one type being homogenously stained for the nerve markers βIII-tubulin and neurofilament and the other showing deficits for these suggesting features of axonal damage. Much more distinct TNFR1/TNFR2 immunoreactions were seen for the latter nerve fascicles. TNFR1 was seen in axons, TNFR2 mainly in Schwann cells. TNFR1 and particularly TNFR2 were seen in walls of parts of blood vessels. The dispersed cells showed frequently TNFR1 and TNFR2 immunoreactivity. These findings suggest that TNF-α can be related to degenerative events but also attempts for healing concerning the nerve structures. The marked expression of the TNF-α system in the peritendinous tissue suggests an impact of TNF-α in tendinopathy/tennis elbow.