Vascular wall cells contribute to tumourigenesis in cutaneous neurofibromas of patients with neurofibromatosis type 1. A comparative histological, ultrastructural and immunohistochemical study.

Unlabelled: Neurofibromas are benign nerve sheath tumours. They occur sporadically, singly or few in number, and in neurofibromatosis type 1 (NF1), an autosomal inherited disease. These tumours are composed of different cell types, e.g. nerve cells (axons and axon sheaths), Schwann cells, mast cells, and fibroblasts. The local control of tumour growth in NF1 is poorly understood. Identification of cell markers could provide new information on the processes that are involved in tumour growth.

Materials And Methods: NF1 patients were diagnosed according to the revised NF1 diagnostic criteria proposed by the US National Institute of Health. Fifteen cutaneous neurofibromas from eight patients (origin: trunk and face) were excised, immediately immersion-fixed in Bouin's fixative and embedded in paraffin. Six micrometre thin sections were incubated with a variety of neuronal markers, connective tissue and glial cell markers, neurotrophic factors and their receptors. In addition, material was fixed, embedded and further processed for light and electron microscopic studies.

Results: The tumours were composed of different cell types, e.g. nerve cells (axons and axon sheaths), Schwann cells, mast cells, compartmentalising cells and fibroblasts. Neuronal markers were identified in axons (neuron-specific protein gene product 9.5, PGP9.5), in several cell types (neurofilament protein-200 kDa, NF-200) and glial cells (protein S-100, S-100). In glial cells the immunoreactivity for fibroblast surface protein (FSP) was scanty, low for cyclic 2,3-nucleotide 3'-phosphodiesterase (CNPase), strong for glucose transporter 1 (Glut-1) but lacking for glial fibrillary acidic protein (GFAP). Schwann cells and so-called compartmentalising cells exhibited immunoreactivity for neurotrophin receptor protein TrkA (TrkA) and glial cell-derived neurotrophic factor (GDNF). GDNF receptor α-1 (GFR-α1) exhibited distinct immunoreactivity in single axons, in Schwann cells, and with lower intensity in some perineurial sheet cells. No immunoreactivity was observed for the low-affinity neurotrophin receptor protein p75(NTR), high-affinity receptor protein TrkB (TrkB), high-affinity receptor protein TrkC (TrkC), the neurotrophin 3 (NT-3), and the brain-derived neurotrophic factor (BDNF).

Conclusion: Human cutaneous neurofibromas displayed a pattern of neurotrophic factors and their receptor immunoreactivity, which is characteristic of differentiated non-malignant tumours, and exhibited some differences from that established in developing and differentiated control Schwann cells (probably involved in the pathogenesis of the neurofibromas), as well as tumour cells in the process of differentiation. Neurofibromas are highly vascularized tumours and possess activated endothelial cells and pericytes. We presume that most of the hyperplastic structural components of a neurofibroma are generated from activated pericytes and smooth muscle cells of the small tumour vessels which possess qualities of adult stem cells.