Lymphoid organs are supplied by many nerve endings associated with different kinds of cells and macrophages. The role of these neuromediators on the release of locally active molecules is still unknown. Here we focused our attention on the expression of some neurotrophins (NTs), their high- and low-affinity receptors and several neurotransmitters in human palatine tonsils. Light and electron microscopy immunohistochemistry showed that human tonsillar samples were positive for all analyzed neurotrophins (NGF, BDNF and NT-3) and their high-affinity receptors (TrkA, TrkB and TrkC, respectively). All of these molecules were strongly expressed in macrophages whereas, in some patients, a weaker specific staining of lymphocytes and blood vessels was also found. The low-affinity receptor for NGF (p75) was always absent in the analysed samples. RT-PCR confirmed the occurrence of specific transcripts for NTs and their high-affinity receptors as well as the absence of mRNA for p75 protein. Also, specific immunoreactivity for neurotransmitters SP, VIP, CGRP, ChAT and nNOS was mainly expressed by macrophagic cells. These results suggest the presence of an extensive network of innervation in the human palatine tonsils which may play a role in the regulation of some immune functions as well as in the modulation of a possible functional scenario of interactions among different immune cellular subtypes.
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