Plasma and wound fluids from trauma patients suppress neutrophil extracellular respiratory burst.

Background: Trauma increases susceptibility to secondary bacterial infections. The events suppressing antimicrobial immunity are unclear. Polymorphonuclear neutrophils (PMNs) migrate toward bacteria using chemotaxis, trap them in extracellular neutrophil extracellular traps, and kill them using respiratory burst (RB). We hypothesized that plasma and wound fluids from trauma patients alter PMN function.

Methods: Volunteer PMNs were incubated in plasma or wound fluids from trauma patients (days 0 and 1, days 2 and 3), and their functions were compared with PMNs incubated in volunteer plasma. Chemotaxis was assessed in transwells. Luminometry assessed total and intracellular RB responses to receptor-dependent and independent stimulants. Neutrophil extracellular trap formation was assessed using elastase assays. The role of tissue necrosis in creating functionally suppressive systemic PMN environments was assessed using a novel pig model where PMNs were incubated in uninjured pig plasma or plasma from pigs undergoing intraperitoneal instillation of liver slurry.

Results: Both plasma and wound fluids from trauma patients markedly suppress total PMN RB. Intracellular RB is unchanged, implicating suppression of extracellular RB. Wound fluids are more suppressive than plasma. Biofluids suppressed RB maximally early after injury and their effects decayed with time. Chemotaxis and neutrophil extracellular trap formation were suppressed by biofluids similarly. Lastly, plasma from pigs undergoing abdominal liver slurry instillation suppressed PMN RB, paralleling suppression by human trauma biofluids.

Conclusion: Trauma plasma and wound fluids suppress RB and other key PMNs antimicrobial functions. Circulating suppressive signals can be derived from injured or necrotic tissue at wound sites, suggesting a key mechanism by which tissue injuries can put the host at risk for infection.