Role of IL-8 and ICAM-1 in polymorphonuclear leukocyte (PMN) migration through respiratory syncytial virus (RSV)-infected pulmonary epithelial cells

Previous studies have shown that RSV infection of the lower airway results in transepithelial migration of PMNs into the airway lumen, the mechanisms of which are unknown. We have also shown that RSV-infected epithelial cells release interteukin-8 (IL-8), and express intercellular adhesion molecule-1 (ICAM-1), but their functional roles in PMN migration and adhesion have not been evaluated. In the current study, the role of IL-8 and ICAM-1 in adhesion and transepithelial migration of PMNs during RSV infection was investigated using A549 (alveolar epithelial cell line) monolayers grown on cell culture inserts. Purified RSV pool was used to infect confluent monolayere at multiplicity of infection dose of 10. 24 h after infection, neutralizing antibody (Ab) against IL-8 or ICAM-1, or control Ab were mixed in the chamber above the monolayer and incubated for 2 h. 1.5 × 10⁸ human PMNs were inoculated into the upper chamber. 3 h later, the PMNs in the top and bottom chamber, and the fraction adherent to A549 monolayers, were isolated and quantitated by manual counting. The results were expressed as percent change in PMN adhesion and migration as compared to the control. % change in migration % change in adhesion RSV + A549 + control Ab +73.1 +160.8 RSV + A549 + IL-8 Ab 0.0 + 6.2 RSV+ A549 +ICAM-1 Ab + 7.1 + 17.9 RSV infection markedly increased transepithelial migration and adhesion of PMNs when compared to sham (control) infection (p < 0.005). However, IL-8 and ICAM-1 antibodies blocked this migration and adhesion of PMNs during RSV infection (p <0.005). In conclusion, the increased PMN transmigration through and adherence to alveolar epithelial cells during RSV infection is primarily mediated by IL-8 and ICAM-1. It is likely that IL-8 increases the expression of PMN-Mac-1, and ICAM-1 interacts directly with PMN Mac-1.