79 Burn Injury Alters Pulmonary Neutrophil Extracellular Trap (NET) Formation

Abstract

It is well known that burn patients suffer from serious lung complications such as acute respiratory distress syndrome, acute lung injury and pneumonia. However, the reasons for the development of these conditions after burn injury (BI) are not clearly understood. Several studies have been examined the importance of macrophages after burn injury. However, the involvement of neutrophils in lung complications after BI has not been studied in detail. Particularly, the importance of recently identified neutrophil extracellular traps (NETs) in the lungs after BI is unknown. NETs are considered to help trap infectious agents to protect the host; however, excess NETs could damage and destroy the airways and cause lung dysfunction. We established an in vivo model to study NETosis in the lungs after BI using an LPS model and investigated neutrophil behavior in burn injured individuals with/without LPS-mediated pneumonia. We have first created a 15% body burn, and instilled various amounts of LPS (0–50 µg/kg) into the airways of BALB/c mice. After various time points (30mins, 3 h, 16 h, 1-7day), we have collected bronchoalveolar lavage (BAL) fluid, and lung tissues. Immune cells present in the BAL fluid were deposited on slides by Cytospin preparations, stained and quantified by microscopy. DNA-protein complexes present in the BAL supernatant and lung tissues were analyzed by agarose gel electrophoresis and PicoGreen assays. Presence of a NET marker, citrullinated histone, and further quantification of neutrophils with MPO in the lung, were analyzed by Western blots and immunohistochemistry. The data obtained from these studies show that neutrophils are not detectable in the airways under baseline or after BI; however, different numbers of neutrophils and amounts of NETs were present under various experimental conditions and time points-post BI. These data show that we could measure NET components in the airways of mice instilled with LPS after BI. We have successfully established a mouse model to study pulmonary NETosis in BI, and optimized the range of LPS concentrations and time points necessary to observe differences in NETosis under various experimental conditions. BI reduces the LPS-mediated pulmonary innate immune response. A decrease in innate immune response may be responsible for the increase in pneumonia incidence in patients with BI. This model should help understand the roles of NETs in pulmonary dysfunction after BI, and for testing potential drugs for correcting NET-mediated lung complications.