The essential role of neutrophils in host defense is illustrated by genetic disorders of neutrophil function such as chronic granulomatous disease (CGD), characterized by reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and reactive oxygen species (ROS) production, or leukocyte adhesion deficiency (LAD), characterized by mutations in β2 integrin/CD18 and poor neutrophil chemotaxis, in which patients suffer recurrent infections or the high risk of invasive bacterial and fungal infections in cancer patients with chemotherapy-induced neutropenia. This evidence concerns the gene ITGB2 and chronic granulomatous disease.