Plasma levels of danger-associated molecular patterns are associated with immune suppression in trauma patients

Abstract

Purpose: Danger-associated molecular patterns (DAMPs) released of trauma could contribute to an immune suppressed state that renders patients vulnerable towards nosocomial infections. We investigated DAMP release in trauma patients, starting in the prehospital phase, and assessed its relationship with immune suppression and nosocomial infections.

Methods: Blood was obtained from 166 adult trauma patients at the trauma scene, emergency room (ER), and serially afterwards. Circulating levels of DAMPs and cytokines were determined. Immune suppression was investigated by determination of HLA-DRA gene expression and ex vivo lipopolysaccharide-stimulated cytokine production.

Results: Compared with healthy controls, plasma levels of nuclear DNA (nDNA) and heat shock protein-70 (HSP70) but not mitochondrial DNA were profoundly increased immediately following trauma and remained elevated for 10 days. Plasma cytokines were increased at the ER, and levels of anti-inflammatory IL-10 but not of pro-inflammatory cytokines peaked at this early time-point. HLA-DRA expression was attenuated directly after trauma and did not recover during the follow-up period. Plasma nDNA (r = -0.24, p = 0.006) and HSP70 (r = -0.38, p < 0.0001) levels correlated negatively with HLA-DRA expression. Ex vivo cytokine production revealed an anti-inflammatory phenotype already at the trauma scene which persisted in the following days, characterized by attenuated TNF-α and IL-6, and increased IL-10 production. Finally, higher concentrations of nDNA and a further decrease of HLA-DRA expression were associated with infections.

Conclusions: Plasma levels of DAMPs are associated with immune suppression, which is apparent within minutes/hours following trauma. Furthermore, aggravated immune suppression during the initial phase following trauma is associated with increased susceptibility towards infections.

Keywords: DAMPs; Immune suppression; Infection; Injury; Trauma.

Fig. 1

Plasma DAMP and cytokine levels. Plasma levels of nDNA (nuclear DNA, indicator of general DAMP release, a), mtDNA (mitochondrial DNA, DAMP, b), HSP70 (DAMP, c), and cytokines (d–f) in trauma patients and healthy controls. The number of patients/controls included at each time-point is indicated below each time-point. *p < 0.05 compared with healthy controls, pre-hosp prehospital, Er emergency room

Fig. 2

Markers of immune suppression. Leukocyte HLA-DRA mRNA expression in trauma patients and healthy controls, expressed as fold change compared with PPIB (a). Cytokine concentrations in supernatants after 24 h of whole-blood LPS stimulation in patients during the first 3 days after trauma and in healthy controls (b–d). The number of patients/controls included at each time-point is indicated below each time-point. *p < 0.05 compared with healthy controls, pre-hosp prehospital, Er emergency room

Fig. 3

Relationship between change in HLA-DRA expression and development of infections during the first 28 days following trauma. Thirty-three (20 %) patients developed an infection within 28 days following trauma. Patients exhibiting a decrease in HLA-DRA expression between ER and day 3 (ratio <1) were more likely to develop an infection compared with those who showed an increase (ratio >1). Symbols placed on lines indicate censored patients because of death

Fig. 4

Conceptual figure of how DAMP release may lead to increased susceptibility towards infections following trauma. Trauma results in the release of DAMPs including, but not limited to, nDNA and HSP70. Subsequently, DAMPs bind to (intracellular) receptors on immune cells such as macrophages, which induces a predominantly anti-inflammatory response characterized by IL-10 release. In turn, this leads to immune suppression, indicated by decreased monocytic HLA-DR expression as well as reduced production of TNF-α/IL-6 and increased production of IL-10 upon ex vivo stimulation with LPS. Alternatively, DAMPs can exert direct immunosuppressive effects, such as HSP70-induced LPS tolerance in monocytes. All these events take place in the very early (prehospital) phase following trauma. In the hospital, aggravated immune suppression is associated with increased susceptibility towards infections, consequent prolonged ICU and hospital length-of-stay, and increased late mortality