Ishikawa et al. reported that susceptibility to 2° bacterial infection after influenza was secondary to neutrophil dysfunction when mice were infected with Pseudomonas aeruginosa4 days after PR8 infection due to a decrease in granulocyte colony-stimulating factor activity (25), accompanied by decreased myeloperoxidase (MPO) activity, in the bronchoalveolar lavage fluids of mice infected with PR8 and then P. aeruginosa (25). This evidence concerns the gene CSF3 and bacterial infectious disease.