Direct Airway Instillation of Neutrophils Overcomes Chemotactic Deficits Induced by Injury

Abstract

Background: Trauma induces neutrophil migration toward injury sites, both initiating wound healing and protecting against local bacterial infection. We have previously shown that mitochondrial formyl peptides (mtFPs) released by injured tissues act as chemoattractants by ligating neutrophil (PMN) formyl peptide receptor 1 (FPR1). But this process can also internalize multiple neutrophil chemoattractant receptors and thus might limit neutrophil migration to the lung in response to bacteria. Our objective was to better understand susceptibility to pneumonia after injury and thus find ways to reverse it. Methods and Results: We modeled the alveolar chemotactic environment in pulmonary infections by incubating Staphylococcus aureus or Escherichia coli with peripheral blood mononuclear cells. Survey of the chemotactic mediators in the resultant conditioned media (CM) showed multiple potent chemoattractants. Pretreating PMN with mtFPs to mimic injury potently reduced net migration toward CM and this net effect was mostly reversed by an FPR1 antagonist. Using an established mouse model of injury-dependent lung infection, we then showed simple instillation of exogenous unstimulated human neutrophils into the airway resulted in bacterial clearance from the lung. Conclusion: Injury-derived mtFPs suppress global PMN localization into complex chemotactic environments like infected alveoli. Transplantation of naive exogenous human neutrophils into the airway circumvents that pathologic process and prevents development of post-traumatic pneumonia without injury noted to the recipients.

Can Neutrophils Prevent Nosocomial Pneumonia after Serious Injury?

“…Finally, we applied human PMN to our mouse model described in Figure 1 to determine whether human PMN can clear bacteria in the lungs without damaging lungs. CONand PMN-treated group showed significantly increased bacterial clearance in the lungs (Figure 5) [44]. We also observed mice for up to 28 days after the application of human PMN.…”

“…To mimic sterile, typical abdominal extrapulmonary injury in humans, we instilled mtDAMPs intraperitoneally (i.p.). This injury decreased the number of PMN migrating toward secondary infection in the lungs, thus bacterial clearance was reduced compared to control mice [7,14,44].…”

“…Mean and SE values are shown. *: denotes a significant difference by one-way ANOVA, Tukey [44]. *: p = 0.0129, **: p = 0.0020. ns: not significant.…”

The immune suppressive properties of damage associated molecular patterns in the setting of sterile traumatic injury

“…Detected by surface expressed formyl peptide receptor (FPR) 1 and FPR2 ( 67 ), mtFPs are neutrophil chemoattractants, with the proteins that most closely resemble bacterial-derived formylated peptides, namely ND3, ND4, ND5 and ND6 possessing the greatest chemotactic potency ( 66 ). Data generated by several studies have demonstrated that neutrophils pre-treated with ND6 exhibit reduced calcium fluxes, chemotactic responses and ROS production upon secondary stimulation with other GPCR agonists such as IL-8, leukotriene B4 (LTB 4 ) and fMLP ( 30 , 65 – 68 ). Contributing to this heterologous receptor desensitisation and suppression in anti-microbial functions is an ND6-mediated downregulation of GPCRs, for which activation of GRK2 is a potential underlying mechanistic explanation ( 63 , 65 , 66 , 218 ).…”

What's New in Shock, July 2021?

“…Along this similar theme, Zhang et al (9) examined the role of mitochondrial formyl peptides (mtFPs) released by injured tissue in impaired neutrophil migration to the alveolar space. Using conditioned media generated by exposing peripheral blood mononuclear cells (PBMCs) to bacteria, the authors characterize essential PBMC-derived chemoattractants that are potent drivers of neutrophil chemotaxis.…”