MPO and infection: Incubation with epithelial cells infected for 24 h showed significantly greater expression of myeloperoxidase (MPO) on neutrophils after 1 h and 4 h of incubation than on neutrophils that were incubated with mock-infected ciliated epithelial cells, with a mean (±SEM) fluorescence intensity of 6.5 × 102 ± 1.1 × 102 compared with 2.5 × 102 ± 1.2 × 101 after 24 h of infection (P < 0.0001) (Fig. 5B), with similar findings at 1 h (P = 0.722) and 4 h (P < 0.0001) after 72 h of RSV infection.