Objective: To better understand the neutrophil activation and protease imbalance in respiratory syncytial virus (RSV) bronchiolitis.
Methods: Pediatric patients with RSV bronchiolitis were collected, 11 with the Lowell scores > or = 10 (severe group), and 19 with the Lowell scores < 10 (mild group). 20 RSV bronchiolitis patients in convalescent group, 24 patients with bacterial pneumonia, and 15 patients as control group. The percentages of neutrophils were detected. ELISA was used to detect the concentration of neutrophil elastase (NE) and interleukin (IL)-8, and the elastase inhibition capacity (EIC)/free neutrophil elastase activity were detected by colorimetry. Immunohistochemistry was used to examine the expression of alpha(1) antitrypsin (alpha(1)AT).
Results: The neutrophil percentage, the NE and IL-8 concentration of the RSV bronchiolitis group (0.528, 6.39 x 10(7) kg/L and 13.62 x 10(9) kg/L)were all significantly higher than those of the control (0.074, 2.53 x 10(7) kg/L and 2.64 x 10(9) kg/L) and convalescent groups (0.306, 1.23 x 10(7) kg/L and 5.95 x 10(9) kg/L, all P < 0.05). The neutrophil percentage and IL-8 concentration of the convalescent group were both significantly higher than those of the control group (both P < 0.05). Increased expression of alpha(1)AT in RSV bronchiolitis was found when compared with convalescent infants (0.49 vs 0.09, P < 0.05). The free elastase activity level of the bronchiolitis group was 6/30, not different with 7/24 of pneumonia group, and it was only one in convalescent infants.
Conclusion: Mass of neutrophil aggregation and activation exist in RSV bronchiolitis, as well as protease system imbalance, and may play an important role in the inflammatory response and pathogenesis of RSV bronchiolitis.