INVITRO INCUBATION WITH INFLUENZA-VIRUS PRIMES HUMAN POLYMORPHONUCLEAR LEUKOCYTE GENERATION OF SUPEROXIDE

Viral respiratory illnesses exacerbate asthma, increase airway responsiveness, and enhance the frequency of late asthmatic reactions. A number of mechanisms have been identified to explain how respiratory viral illnesses provoke wheezing, including enhanced inflammatory activity of leukocytes. To further understand how respiratory virus-caused illnesses promote leukocyte-dependent airway injury, the following study evaluated the effect of an in vitro incubation of influenza A virus on human polymorphonuclear leukocyte (PMN) generation of superoxide (O2-). PMNs were isolated from anticoagulated human blood following density gradient centrifugation; purified PMNs were then incubated (37-degrees-C x 30 min) with influenza virus (PMN: virus ratio of 5:1 [egg-infective dose 50%] and 10:1) in the presence of 10% autologous serum. After incubation, the viable PMNs (> 95% exclusion of trypan blue) were activated, by the chemotactic peptide formyl-methionine-leucine-phenylalanine (fMLP), calcium ionophore A23187, or phorbol myristate acetate (PMA), and O2- generation was then measured. Generation of O2- to fMLP and A23187 was significantly enhanced from PMNs that had been incubated with influenza virus. Although influenza virus itself did not generate O2-, it caused a transient increase in intracellular calcium ([Ca2+]i) when measured with Indo-1-loaded cells. These results suggest that influenza virus primes PMNs to generate increased amounts of O2- and that the priming effect is associated with a transient increase in [Ca2+]i. Consequently, we postulate that influenza virus priming produces PMNs of enhanced inflammatory potential to cause greater airway injury, obstruction, and responsiveness during a viral respiratory infection.