Depression of monocyte and polymorphonuclear leukocyte oxidative metabolism and bactericidal capacity by influenza A virus.

Decreased host defense against bacterial disease associated with influenza infection may be related to virus-induced changes in phagocytic cell function. Influenza A virus initiates the respiratory burst in peripheral blood monocytes and polymorphonuclear leukocytes, with a peak chemiluminescent response approximately 3 min after virus is added to the cells in vitro. Electron micrographs of phagocytic cells incubated with influenza virus demonstrated virus attached to the cell membrane and within phagocytic vacuoles. After 20 min of incubation of the virus with phagocytic cells, the chemiluminescent response to opsonized zymosan or phorbol myristate acetate was decreased by 30 to 90%. Phagocytic activity of monocytes and polymorphonuclear leukocytes incubate with influenza virus was normal, but the bactericidal activity was significantly depressed. Influenza A virus therefore stimulates an oxidative burst in monocytes as well as polymorphonuclear leukocytes, leading to a subsequent depression of the oxidative metabolic response and bactericidal capacity of the phagocytic cells.