Biology of neutrophils

Neutrophils play an important role in inflammatory responses that are critical for host defense against infection, contribute to the pathogenesis of chronic inflammatory conditions that involve the sinuses and respiratory tract, and comprise 50–75% of circulating leukocytes in humans. They are the first circulating cells to migrate to the site of infection. Through phagocytosis, the production of reactive oxygen intermediates (ROI), and the release of cytotoxic granule contents, these cells function to contain and eliminate invading microorganisms. Representing a major mechanism of innate immunity, neutrophils also release cytokines and chemokines that initiate and amplify inflammation, as well as contribute to the development of the acquired immune response. Given the toxic nature of an activated neutrophil, these cells are associated with the pathogenesis of inflammatory airway diseases, including chronic obstructive pulmonary disease (COPD) and asthma, as well as acute parenchymal lung conditions such as pneumonia and acute lung injury. This chapter examines the biology of the neutrophil, with a focus on its contribution to inflammation in asthma