Intratracheal instillation of neutrophils rescues bacterial overgrowth initiated by trauma damage-associated molecular patterns

BACKGROUND Nosocomial pneumonias are common in trauma patients and so interventions to prevent and treat nosocomial pneumonia may improve outcomes. Our prior work strongly suggests that tissue injury predisposes to infections like nosocomial pneumonia because mitochondrial debris originating from injured cells contains damage-associated molecular patterns that can reduce neutrophil (PMN) migration into the airway and diminish PMN function in response to bacterial inoculation of the airway. This suggested that putting exogenous normal PMN into the airway might be beneficial. METHODS Postinjury pneumonia (PNA) commonly arises in two groups, early, community-acquired PNA (CAP) and later hospital-acquired PNA (HAP). Posttraumatic early-onset CAP and late-onset HAP were modeled in CD-1 mice using Staphylococcus aureus or Pseudomonas aeruginosa instilled intratracheal (i.t.) at clinically relevant times with or without extrapulmonary injuries mimicked by an intraperitoneal application of mitochondrial damage-associated molecular patterns. We applied bone marrow-derived PMN (BM-PMN) intratracheally to assess their effect on bacterial clearance in the lung. RESULTS BM-PMN instillation i.t. had no untoward clinical effects on recipient animals. In both the early/CAP and late/HAP models, clearance of the bacterial inoculum from the lung was suppressed by mitochondrial debris and restored to uninjured levels by i.t. instillation of exogenous BM-PMN. Furthermore, PMN instillation cleared the inoculum of P. aeruginosa that could not be cleared by uninjured mice. Instillation of PMN into the lung, even across strains (CD-1 vs. C57BL/6) had no injurious effect. CONCLUSION These initial studies suggest PMN instillation (i.t.) is worthy of further study as a potential adjunctive therapy aimed at decreasing the morbidity of lung infections in trauma patients. Moreover, PMN instillation (i.t.) may represent a unique means of preventing or treating pneumonia after serious injury that is completely independent of the need for antibiotic use.