Light and electron microscopic immunohistochemical observations of p75 nerve growth factor receptor-immunoreactive dermal nerves in prurigo nodularis

Prurigo nodularis is an inflammatory skin disease characterized by neurohyp erplasia. Neurotrophins and their receptors play a critical role in nerve g rowth, differentiation, maturation and maintenance, including cutaneous ner ve fiber growth and innervation, They may also be responsible for events re lated to the growth and differentiation control of keratinocytes, To explor e the exact distribution of the p75 low-affinity nerve growth factor recept or (p75 NGFr) in the cutaneous nerve components, p75 NGFr immunofluorescenc e as well as ultrastructural immunohistochemical studies were performed on prurigo nodularis lesional skin and normal human skin samples. The immunofl uorescence results revealed that nerve fibers and bundles mere increased in number and size in lesional upper dermis with stronger p75 NGFr immunoreac tivity than in the corresponding normal tissue. At the ultrastructural leve l, a lot of nerve fibers clustered together in the prurigo nodularis dermal tissue. The axons were enlarged and branched, but the axons themselves sel dom showed any NGFr immunoreactivity. The Schwann cell bodies were extended and irregularly shaped, and tended to separate into many branches envelopi ng the axons, The Schwann cell membrane showed strong p75 NGFr immunoreacti vity. The perineurium cells also revealed strong p75 NGFr immunoreactivity. The Schwann cells inside the perineurium were less p75 NGFr-immunoreactive than those outside the perineurium. The membrane of certain basal keratino cytes showed NGFr immunoreactivity as well. The present results indicate th at overexpression of p75 NGFr in Schwann cells and perineurium cells could contribute to the neurohyperplasia in prurigo nodularis.