Expression of NGF receptors in normal and pathological human thymus.

The expression of NGF receptors was investigated in normal human thymus and in thymic hyperplasias, thymomas and thymic carcinomas. By RT-PCR, we detected TrkAI transcripts encoding for the high-affinity NGF receptor. Western blot analysis showed the presence of both TrkA and p75NGFR proteins. In normal thymuses, epithelial subcapsular and medullar cells were TrkA immunoreactive. Interdigitated medullar cells were stained for both TrkA and p75NGFR. While epithelial cells of normal thymuses or benign thymomas exhibited a TrkA positive-p75NGFR negative phenotype, a switch to a TrkA negative-p75NGFR positive phenotype was observed in malignant epithelial cell tumours and was associated with cell proliferation-associated MIB1 expression. Our results argue for a local role of NGF and its receptors on thymic stromal cells both in normal and neoplastic conditions.