NEUROTROPHIN RECEPTOR-LIKE PROTEINS IN PEYERS-PATCHES

Background The neurotrophins are a family of growth factors that act o n responsive cells through specific high-affinity signal-transducing r eceptors called Trk (A, B, and C) proteins. The neurotrophin receptor proteins are widely distributed in both nervous and nonnervous tissues , including the lymphoid organs. The expression of these receptor prot eins by a cell population is an indication of responsiveness to the re spective binding neurotrophin, The present study investigated the pres ence and cellular localization of high-affinity neurotrophin receptor proteins in equine and bovine Peyer's patches, Methods: Peyer's patche s from horse and cow intestine were fixed in Bouin's fixative, embedde d in paraffin cut 10 mu m thick, and studied immunohistochemically usi ng rabbit polyclonal antibodies against specific epitopes of the intra cellular domain of the Trk receptor proteins. Results: Immunoreactivit y (IR) for Trk-like proteins was found in specific cell populations in Peyer's patches. TrkA-IR in the horse was localized in dendritic cell s of the interfollicular T-cell zones and in follicular dendritic cell s of the lymphoid follicles; in the cow, TrkA-ir was present in reticu lum cells, TrkB-Like IR was present in cells found inside lymphoid fol licles of the horse, probably reticulum cells. Furthermore, in both sp ecies, TrkB-IR, was found in interstitial dendritic cells and/or macro phages of the intestinal lamina propria. No specific TrkC-like immunos taining was found in immunocompetent cells of Peyer's patches. Conclus ions: Present findings demonstrate that, as in other lymphoid organs, the accessory nonlymphoid cells express immunoreactivity for high-affi nity neurotrophin receptor proteins. These results seem to favor the n otion that neurotrophins, especially nerve growth factor, could have a physiological role in secondary lymphoid organs, possibly acting on a ccessory cells and not directly on lymphocytes. (C) 1997 Wiley-Liss, I nc.