Objective: To investigate the expression of nerve growth factor (NGF) in inflammatory cells of induced sputum from patients with asthma.
Methods: Induced sputum samples were collected from 11 asthmatics in exacerbation, 19 asthmatics with stable disease and 11 healthy individuals. Sputum samples of 12 asthmatics with stable disease were collected again after treatment with inhaled corticosteroids (ICS) for 2 weeks. The differential counts of sputum inflammatory cells were studied. NGF was detected using immunocytochemistry and the positive percentages in different cells were measured. Interleukin-5 (IL-5) in sputum supernatants was detected using enzyme-linked immunosorbent assay.
Results: NGF was localized in the plasma of macrophages, lymphocytes and granulocytes. 1. In asthmatics with both exacerbation and stable disease, the NGF positive percentages in macrophages [(77.8 +/- 4.8)% and (68.1 +/- 5.3)%], lymphocytes [(43.2 +/- 9.3)% and (34.2 +/- 11.3)%], and granulocytes [(38.7 +/- 6.2)% and (32.1 +/- 3.7)%] were all significantly higher (P < 0.01) than those in the healthy controls [(37.6 +/- 8.4)%, (12.6 +/- 8.5)%, and (12.7 +/- 8.2)%, respectively]. The differences of those indices between patients with exacerbation and patients with stable disease were also significant (P < 0.01). Patients with exacerbation had significantly elevated levels of IL-5 [(124 +/- 71) ng/L] compared with patients with stable disease [(52 +/- 23) ng/L] and the healthy controls [(26 +/- 12) ng/L] (P < 0.01). 2. In the 12 patients with stable disease evaluated after treatment with ICS, the NGF positive percentages in macrophages [(54.3 +/- 7.3)%], lymphocytes [(22.0 +/- 5.6)%], and granulocytes [(27.0 +/- 4.3)%], and the level of IL-5 [(29 +/- 13) ng/L] were all decreased significantly (P < 0.01) compared with the baselines [(67.0 +/- 5.0)%, (36.0 +/- 9.0)%, (32.0 +/- 3.0)%, and (49 +/- 26) ng/L, respectively]. 3. The NGF positive percentages in both macrophages and granulocytes correlated to the sputum lymphocyte counts (r = 0.723, r = 0.630, P < 0.01; respectively) and the levels of IL-5 (r = 0.652, r = 0.636, P < 0.01; respectively).
Conclusion: The expression of NGF in macrophages and lymphocytes in the airways is upregulated in asthma, which indicates a potential correlation between NGF and airway inflammation in asthma.