Telocytes in neuromuscular spindles

A new cell type named telocyte ( TC ) has recently been identified in various stromal tissues, including skeletal muscle interstitium. The aim of this study was to investigate by means of light (conventional and immunohistochemical procedures) and electron microscopy the presence of TC s in adult human neuromuscular spindles ( NMS s) and lay the foundations for future research on their behaviour during human foetal development and in skeletal muscle pathology. A large number of TC s were observed in NMS s and were characterized ultrastructurally by very long, initially thin, moniliform prolongations (telopodes – Tps), in which thin segments (podomeres) alternated with dilations (podoms). TC s formed the innermost and (partially) the outermost layers of the external NMS capsule and the entire NMS internal capsule. In the latter, the Tps were organized in a dense network, which surrounded intrafusal striated muscle cells, nerve fibres and vessels, suggesting a passive and active role in controlling NMS activity, including their participation in cell‐to‐cell signalling. Immunohistochemically, TC s expressed vimentin, CD 34 and occasionally c‐kit/ CD 117. In human foetus (22–23 weeks of gestational age), TC s and perineural cells formed a sheath, serving as an interconnection guide for the intrafusal structures. In pathological conditions, the number of CD 34‐positive TC s increased in residual NMS s between infiltrative musculoaponeurotic fibromatosis and varied in NMS s surrounded by lymphocytic infiltrate in inflammatory myopathy. We conclude that TC s are numerous in NMS s (where striated muscle cells, nerves and vessels converge), which provide an ideal microanatomic structure for TC study.