Background: Nerve growth factor (NGF) is a neurotrophic cytokine with immunomodulatory activity. NGF contributes to neurogenic inflammation and has been described in asthma and idiopathic pulmonary fibrosis.
Objectives: To identify and quantify NGF in serum and peripheral blood lymphocyte cultures from pigeon fanciers, and to investigate an association with the immune response to inhaled avian antigens, and with symptoms of acute hypersensitivity pneumonitis (HP).
Methods: NGF was quantified and compared with serum IgG antibody against inhaled avian antigens, with serum C-reactive protein (CRP), and with KL-6, a marker of lung interstitial inflammation. These were measured using enzyme-linked immunoassay. Levels were compared with symptom history in 55 pigeon fanciers (26 subjects with acute HP but symptom-free at the time of testing) and 15 subjects with no avian exposure.
Results: Pigeon fanciers had higher-than-normal serum IgG antibody, CRP, and KL-6 levels (p < 0.01 each). These measures were unrelated to HP symptom category; instead, in all pigeon fanciers, the concentrations of CRP and KL-6 correlated with each other and with the antibody titers (p < 0.01 each). Serum NGF levels were normal; however, NGF production by mitogen-activated lymphocytes was higher than normal, and correlated with IgG antibody titer (p < 0.05) and with serum CRP (p < 0.05).
Conclusions: Serum NGF was normal in pigeon fanciers; however, their blood lymphocytes ex vivo synthesized increased NGF in concentrations that correlated with the titer of serum IgG antibody to inhaled avian antigens. These also correlated with CRP and KL-6 levels, suggesting that antigen exposure in seropositive subjects is associated with subclinical inflammation involving coordinated synthesis of neurotrophin and immune mediators.