Involvement of the NGF receptors (Trka and p75(Ingfr)) in the development and maintenance of the thymus

Nerve growth factor (NGF) and its main low- (p75(LNGFR)) and high-affinity (TrkA) receptors have been found in the vertebrate thymus, thus suggesting they are involved in the control of thymic function. However, its role in t his organ is poorly known. In the present study we used combined morphologi cal and immunohistochemical techniques to analyze the distribution of TrkA and p75(LNGFR) in the rat thymus, as well as the structural changes in the thymus of p75(LNGFR) or TrkA deficient mice. In adult rats both TrkA and p7 5(LNGFR) were localized in a subset of thymic epithelial cells found primar ily in the subcapsular and medullary thymic regions, regarded to be endoder mal-derived cells. Consistently, animals with a non-functional TrkA but not those lacking p75(LNGFR), showed structural changes consisting of a decrea se in the density of thymocytes, absence of cortico-medullary border, and l arge cysts lined of endodermal epithelium. These results strongly suggest a function of the TrkA-NGF system in thymic functions mediated by epithelial cells, as well as a role of TrkA in the development of the murine thymus. The function of p75(LNGFR) remains to be established.