Pneumonia in the first week after polytrauma is associated with reduced blood levels of soluble herpes virus entry mediator

Abstract

Background: Pneumonia develops frequently after major surgery and polytrauma and thus in the presence of systemic inflammatory response syndrome (SIRS) and organ dysfunction. Immune checkpoints balance self-tolerance and immune activation. Altered checkpoint blood levels were reported for sepsis. We analyzed associations of pneumonia incidence in the presence of SIRS during the first week of critical illness and trends in checkpoint blood levels.

Materials and methods: Patients were studied from day two to six after admission to a surgical intensive care unit (ICU). Blood was sampled and physician experts retrospectively adjudicated upon the presence of SIRS and Sepsis-1/2 every eight hours. We measured the daily levels of immune checkpoints and inflammatory markers by bead arrays for polytrauma patients developing pneumonia. Immune checkpoint time series were additionally determined for clinically highly similar polytrauma controls remaining infection-free during follow-up. We performed cluster analyses. Immune checkpoint time trends in cases and controls were compared with hierarchical linear models. For patients with surgical trauma and with and without sepsis, selected immune checkpoints were determined in study baseline samples.

Results: In polytrauma patients with post-injury pneumonia, eleven immune checkpoints dominated subcluster 3 that separated subclusters 1 and 2 of myeloid markers from subcluster 4 of endothelial activation, tissue inflammation, and adaptive immunity markers. Immune checkpoint blood levels were more stable in polytrauma cases than controls, where they trended towards an increase in subcluster A and a decrease in subcluster B. Herpes virus entry mediator (HVEM) levels (subcluster A) were lower in cases throughout. In unselected surgical patients, sepsis was not associated with altered HVEM levels at the study baseline.

Conclusion: Pneumonia development after polytrauma until ICU-day six was associated with decreased blood levels of HVEM. HVEM signaling may reduce pneumonia risk by strengthening myeloid antimicrobial defense and dampening lymphoid-mediated tissue damage. Future investigations into the role of HVEM in pneumonia and sepsis development and as a predictive biomarker should consider the etiology of critical illness and the site of infection.

Keywords: critical illness; herpesvirus entry mediator; immune checkpoint; immunosuppression; pneumonia; polytrauma; sepsis; systemic inflammatory response syndrome.

Figure 1

Flow diagram for selection of polytrauma (red) and non-polytrauma (surgical trauma) (blue) patients for the first and second part of the analysis, respectively, from the study population. At the beginning of August 2018, a completed 5-day follow-up series of frozen blood plasma with complete expert adjudication according to Sepsis-1/2 was available for 63 patients and an extra 20 patients until the end of the study period. Among the latter were seven polytrauma patients (gray) that were not considered.

Figure 2

Alignment of expert label timelines for the included paired blood plasma samples. Cases and controls were polytrauma patients with a direct SIRS-to-sepsis transition, namely pneumonia development, and without a sepsis label, respectively, during follow-up. Sepsis was adjudicated by clinical experts according to Sepsis-1/2. Consecutive sampling time points are indicated, starting at 3 PM on ICU-day two (0 h), i.e. study inclusion. Sampling time points, for which samples were included in the analysis as explained in the main text, are shown. Patient identification numbers of cases and controls in a given pair are printed in bold type to the left of the corresponding aligned expert label timelines, which are color-coded as indicated. The black up-pointing triangle indicates sepsis onset. The time points for the samples obtained after sepsis onset are printed in bold type.

Figure 3

Heat map of 16 soluble immune checkpoints and 51 inflammatory and organ dysfunction marker levels in the blood plasma of seven polytraumatized patients developing pneumonia. Tiles are arranged horizontally by consecutive inclusion and by sample time point (cf. Figure 2 ). Black boxes are drawn around tiles of time points, on which patients were adjudicated septic by clinical experts according to Sepsis-1/2. The lung constituted the infectious focus in all cases. Analytes are hierarchically clustered using Euclidean distance and complete linkage. Four subclusters, 1–4, are indicated. IC: Soluble immune checkpoint proteins; Cytokine: Markers of inflammation and organ dysfunction.

Figure 4

Clustered heat map of soluble immune checkpoint levels in seven polytrauma post-injury pneumonia cases and matched infection-free controls. Data were log-transformed. Analytes are hierarchically clustered using Euclidean distance and average linkage. Cases and controls each are arranged by consecutive inclusion and sampling time point (cf. Figure 2 ). Two subclusters, A and B, are indicated.

Figure 5

Immune checkpoint receptor-ligand pairs. The protein symbols of the 16 immune checkpoints analyzed in this study are arranged in an oval and by the clustering result displayed in Figure 4 with subclusters A and B indicated. The rainbow color scheme reflects adjacency in the dendrogram of the cluster analysis. Reported receptor-ligand pairs among them are identified by connecting lines. Supporting literature for these receptor-ligand interactions is assembled in Supplementary Table 6 .

Figure 6

Time trends in soluble immune checkpoints in polytrauma post-injury pneumonia cases and matched infection-free controls. Sepsis was adjudicated according to Sepsis-1/2 by clinical experts. The lung constituted the infectious focus in all cases. Trajectories of measured blood plasma concentrations are overlaid with estimated time trends from hierarchical linear models (see legend on the top-left). *p < 0.05 after Bonferroni adjustment.

Figure 7

Study baseline blood levels of HVEM and ICOS in polytrauma and non-polytrauma patients with and without sepsis according to Sepsis-1/2 based clinical expert adjudication. Concentrations are plotted on a log scale. Differences across all groups were assessed with the Kruskal-Wallis test followed by Dunn’s test for multiple comparisons. * p < 0.05, ** p < 0.005.