Neutrophils in the lung: "the first responders"

Neutrophils, constituting the first line of defense, perform vital functions during immune surveillance. A key feature that assists in their prompt response to an inflammatory signal is rapid migration to the affected site. They are normally short-lived but can be activated to live longer under the influence of an inflammatory stimulus. They can, thereby, release their toxic granule contents that are differentially housed inside the cytoplasm. Although these events are well characterized in the peripheral circulation, we are still far from fully understanding their recruitment in lungs. Lungs are a reservoir of neutrophils under steady-state. In the event of an infection or injury, they promptly activate and recruit to the alveolar compartment as well as the airways. Lung intravital microscopy has revealed that neutrophils display novel features during steady- and activated-state highlighting key differences in the lung vasculature compared to peripheral sites. This review will discuss neutrophil biology in lung inflammation and will highlight the role of angiostatin, an anti-angiogenic molecule, as well as vitronectin, an acute phase secreted plasma protein, in lung neutrophil recruitment.