A Potential Mechanism for Immune Suppression by Beta-Adrenergic Receptor Stimulation following Traumatic Injury

Abstract

Background: β-Adrenergic agents suppress inflammation and may play an important role in posttraumatic infections. Mechanisms may include inhibition of MAP kinase signaling. We sought to determine whether MKP-1 contributed to catecholamine suppression of innate immunity and also wanted to know whether early catecholamine treatment after traumatic injury increases the risk of later nosocomial infection. Methods: We performed experiments using THP-1 cells and peripheral blood mononuclear cells from healthy individuals. We exposed cells to epinephrine and/or LPS and measured inflammatory gene transcription and MAP kinase activation. We inhibited MKP-1 activity to determine its role in catecholamine-induced immune suppression. Finally, we studied injured subjects to determine whether early catecholamine treatment was associated with nosocomial infection. Results: Epinephrine increases MKP-1 transcripts and protein and decreases LPS-induced p38 and JNK phosphorylation and TNF-α gene transcription. RNAi inhibition of MKP-1 at least partially restores LPS-induced TNF-α gene expression (p = 0.024). In the clinical cohort, subjects treated with β-adrenergic agents had an increased risk of ventilator-associated pneumonia (aOR = 1.9; 95% CI = 1.3–2.6) and bacteremia (aOR = 1.5; 95% CI = 1.1–2.3). Conclusions: MKP-1 may have a role in catecholamine-induced suppression of innate immunity, and exogenous catecholamines might contribute to nosocomial infection risk.