Cellular localization of the Trk neurotrophin receptor family in human non-neuronal tissues

We investigated the distribution of the high-affinity neurotrophin receptors TrkA, TrkB, and TrkC in a wide range of normal non-neuronal tissues of adult human by immunohistochemical methods. Trk immunoreactivity (IR) was detected at various levels in all tissues examined, except for the heart and liver. The gastric parietal cells showed strong TrkA and TrkC IR and all of the Trks had IR for the putative intestinal neuroendocrine cells. In the pancreas, TrkA and TrkC IR was detected in the sub-intralobular ducts, whereas TrkB IR was found specifically in the alpha-islet cells. The lymph node and spleen exhibited TrkB IR in monocytes/macrophages. The adrenal cortex showed selective TrkA IR with TrkC IR in the medulla. In the reproductive system, TrkA IR was detected in the prostatic epithelial cells, TrkC in the ovarian theca and granulosa cells, TrkA and TrkC in the secretory-phase endometrium, and TrkA in the mammary ducts. The kidney showed strong TrkA and TrkC IR in it tubules, but no Trk receptors were present in the glomeruli. In the skin, TrkA and TrkB/TrkC were present in the basal and granular layers of the epidermis, respectively.