Time course correlations of lung function, inflammation and viral titre after airways infection with parainfluenza-3

S. M Chidgey & K. J Broadley, Welsh School of Pharmacy, Cardiff University, King Edward VII Avenue, Cardiff. CF10 3XF. UK.

In children, the paramyxovirdae are the most important family of viruses causing acute respiratory infections, with respiratory syncytial virus and parainfluenza viruses most widespread (Glezen, 1973). Acute infection with parainfluenza-3 (PI-3) in children accounts for a significant portion of infantile croup, bronchiolitis and pneumonia (Welliver et al., 1982). In this study, a time course investigating both functional and morphological changes in PI-3 virus-infected guinea pigs was determined.

M ale, Dunkin-Hartley guinea pigs (200-250g) were assessed for airway reactivity to histamine (1mM, 20 seconds, nose-only). Whole body plethysmography measured airway function in conscious guinea pigs, recorded as specific airway conductance (sGaw) for 10 minutes after exposure. 24 hours later guinea pigs were inoculated with 250μl PI-3 virus (5.0x106) or virus-free medium (Vero cell supernatant) by intranasal instillation. Guinea pigs were assessed 1, 2, 4, 7, 25 or 40 days post infection (6 animals per study day) f or airway reactivity to histamine and within 20 minutes received a lethal dose of pentobarbitone sodium. Bronchoalveolar lavage (BAL) was performed and lung tissue removed. BAL fluid was analysed for total and differential inflammatory cell counts, total nitric oxide metabolites and protein. Lung tissue was used for determining wet lung weights, histological analysis (haematoxylin & eosin staining) and viral titre using TCID50 analysis, which refers to the quantity of virus required to infect 50% of vero cells in culture. Respiratory rate and lung function were measured at appropriate time points. Statistical analysis was by analysis of variance followed by paired Student’s t tests and Bonferroni multiple comparison tests. p<0.05 was considered significant.

Prior to viral inoculation or after virus-free medium, histamine produced no bronchoconstriction. However, following infection a significant bronchoconstriction was observed with peak reductions in sGaw of - 40.0±5.4% H2O-1sec-1, indicating airway hypereactivity (AHR). Peak inflammatory cell increases were also observed 4 days post inoculation with a significant increase in total ( 8.1 ± 0.3 x106 cells ml-1) and differential cell counts of macrophages (6.4 ± 0.2 x106 cells ml-1), eosinophils (1.4 ± 0.1 x106 cells ml-1) and neutrophils (0.3 ± 0.1 x106 cells ml-1) compared to virus-free medium controls (2.0±0.1, 1.8±0.1, 0.2±0.01, 0.02±0.01 x106 cells ml-1 respectively). Peak significant increases were also observed in nitric oxide (93.3±3.3 μM 100 μ-1), protein (1793.6±50.9 μg ml-1) and wet lung weights 11.8±0.3 g Kg-1) 4 days post infection as an index of lung inflammation compared to virus-free medium inoculated animals (44.2±2.3 μM 100 μl-1, 992.7±35.9 µg ml-1, 6.7±0.3 g Kg-1 respectively). No changes were observed in lung function, but respiratory rate increased significantly peaking 4 days post infection (160±5.9 breaths min-1) compared to virus-free medium inoculated guinea pigs (72.0±7.0 breaths min-1). Histopathology of virus-infected lung tissue showed evidence of alveolitis, peribronchiolitis and interstitial pneumonitis. PI-3 replication in the lung peaked 4 days post infection (19242173.9±7764101.8 TCID50 units ml-1). All parameters except AHR returned to baseline at 40 days. In conclusion, there is close correlation between viral infection and lung inflammation and function.

Glezen et al. (1973). N. Eng. J. Med. 239-243.
Welliver et al. (1982). J. Pediatr. 101: 180-187.

Supported by a BBSRC studentship to Sharon Chidgey.