Despite being a well-characterized neurotrophic factor, nerve growth factor (NGF) influences survival, differentiation, and functions of mast cells. We investigated whether NGF was able to induce directional migration of rat peritoneal mast cells (PMCs). NGF clearly induced chemotactic movement of PMCs in a dose-dependent manner with the drastic morphological change and distribution of F-actin, which was completely blocked by pretreatment with Clostridium botulinumC2 toxin, an actin-polymerization inhibitor. Because PMCs constitutively express the NGF high-affinity receptor (TrkA) with a tyrosine kinase domain, we focused on downstream effectors in signaling cascades following the TrkA. NGF rapidly activated both mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K), and the addition of inhibitors specific for MAPK kinase and PI3K suppressed cell migration and these signals. In the coculture system with PMCs and fibroblasts, which produce biologically active NGF, directional migration of PMCs to fibroblasts was observed, and the addition of anti-NGF polyclonal antibodies significantly suppressed the migration of PMCs. These findings suggested that NGF initiated chemotactic movement of PMCs through both MAPK and PI3K signaling pathways following TrkA activation. Thus, locally produced NGF may play an important role in mast cell accumulation in allergic and nonallergic inflammatory conditions.

The stimulating effect of nerve growth factor (NGF) on phagocytosis, parasite killing, and interleukin-1beta (IL-1beta) production of murine peritoneal macrophages was assessed. In the presence of various doses of NGF, macrophages showed the increased phagocytosis of both nonspecific hydrophilic microspheres and sheep red blood cells (SRBC) opsonized with anti-SRBC antibodies (Ab) or complement in a dose-dependent manner. NGF also enhanced killing of Leishmania donovani promastigotes by macrophages, and its ability was comparable with that of an optimal dose of recombinant granulocyte-macrophage colony-stimulating factor or recombinant interferon-gamma. The addition of NGF to peritoneal macrophages and monocyte-macrophage J774A.1 cells led to a significant release of IL-1beta in a dose-dependent manner and expression of IL-1beta mRNA. Because pretreatment of peritoneal macrophages and J774A.1 cells with K-252a, a tyrosine kinase inhibitor, completely suppressed these NGF-mediated stimulating effects and p140trk phosphorylation and because flow cytometric analysis with specific Ab against two distinct NGF receptors showed the expression of p140trk, unlike p75LNGFR, on the surface of macrophages, the stimulating activity of NGF to murine macrophages may be mediated through p140trk. Thus, NGF may act as an activator for murine macrophages in the process of inflammatory and immune actions.

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