Depression of rat neutrophil exudation and motility by influenza virus.

Purified influenza A and B viruses (3000 HA units) were injected intraperitoneally into rats. 1 h later the animals were given starch solution intraperitoneally, after which the number and composition of the exuded cells were determined at intervals. Both influenza A and B viruses depressed neutrophil exudation into the peritoneal cavity for a period of 10 to 17 h after the starch injection. The exudation of leukocytes other than neutrophils (a mixture of mononuclear cells and 5% to 10% eosinophils) was depressed for 17 h after starch injection by influenza A virus. When tested in vitro by a modification of the Boyden method, the peritoneal exudate neutrophils from virus-treated animals exhibited significantly depressed chemotaxis and consistently, although not always significantly, reduced chemokinesis (migration in the presence of a chemoattractant without a gradient) and random locomotion. Both influenza A and B viruses inhibited in vitro the motility of starch-induced peritoneal exudate neutrophils in Boyden chambers after a virus-cell interaction of 60 min at 37 degrees C. The present findings support the concept that impaired neutrophil exudation caused by depressed motility is one mechanism responsible for the increased susceptibility to bacterial superinfection during influenza.