Neurotrophin and neurotrophin receptor expression in alveolar macrophages:An immunocytochemical study

Alveolar macrophages play a crucial role in regulating lung immune response s and in maintaining the integrity of the respiratory tract. Neurotrophins (NTs), besides to their neurotrophic activities, exhibit physiological effe cts in the immune system. In this study, nerve growth factor (NGF), brain d erived neurotrophic factor (BDNF), NT-3 and low-(p75) and high affinity (Tr ks) NT receptors were investigated by immunocytochemistry in cytospin centr ifuged preparations of human alveolar macrophages. Approximately 2.5% alveo lar macrophages were immunoreactive for NGF, whereas no macrophages display ing immunoreactivity for BDNF or NT-3 were observed. A 3.5% macrophages dis played immunoreactivity for TrkA-receptor protein, 10% for TrkB-receptor pr otein (full length isoform), and 2% for TrkC-receptor protein. No low-affin ity p75 NT and TrkB/-/ truncated isoform receptor immunoreactive macrophage s were found. These findings support the hypothesis that NTs and the corres ponding receptors may play a role in regulating immunological and functiona l activity of alveolar macrophages via paracrine/autocrine mechanisms.