Differential expression of NGF receptors in human thymic epithelial tumors

NGF receptor (TrkA and p75(NGFR)) expression was investigated in human thym uses, including normal thymuses, thymic hyperplasias, thymomas and thymic c arcinomas. TrkAI but not TrkAII transcripts were demonstrated by RT-PCR. In normal thymuses, immunohistochemistry revealed a restricted TrkA-immunorea ctivity to epithelial and interdigitated reticular cells, while only interd igitaded reticular cells were immunoreactive for p75(NGFR). Thymocytes were negative for both receptors. A switch from the normal TrkA positive-p75(NG FR) negative phenotype to a TrkA negative-p75(NGFR) positive phenotype was found in histologically aggressive epithelial cell tumors, suggesting that NGF and its receptors are potentially involved in thymus stroma organogenes is and proliferation.