Alveolar compartmentalization of inflammatory and immune cell biomarkers in pneumonia-related ARDS

Abstract

Background: Biomarkers of disease severity might help individualizing the management of patients with the acute respiratory distress syndrome (ARDS). Whether the alveolar compartmentalization of biomarkers has a clinical significance in patients with pneumonia-related ARDS is unknown. This study aimed at assessing the interrelation of ARDS/sepsis biomarkers in the alveolar and blood compartments and explored their association with clinical outcomes.

Methods: Immunocompetent patients with pneumonia-related ARDS admitted between 2014 and 2018 were included in a prospective monocentric study. Bronchoalveolar lavage (BAL) fluid and blood samples were obtained within 48 h of admission. Twenty-two biomarkers were quantified in BAL fluid and serum. HLA-DR⁺ monocytes and CD8⁺ PD-1⁺ lymphocytes were quantified using flow cytometry. The primary clinical endpoint of the study was hospital mortality. Patients undergoing a bronchoscopy as part of routine care were included as controls.

Results: Seventy ARDS patients were included. Hospital mortality was 21.4%. The BAL fluid-to-serum ratio of IL-8 was 20 times higher in ARDS patients than in controls (p < 0.0001). ARDS patients with shock had lower BAL fluid-to-serum ratio of IL-1Ra (p = 0.026), IL-6 (p = 0.002), IP-10/CXCL10 (p = 0.024) and IL-10 (p = 0.023) than others. The BAL fluid-to-serum ratio of IL-1Ra was more elevated in hospital survivors than decedents (p = 0.006), even after adjusting for SOFA and driving pressure (p = 0.036). There was no significant association between alveolar or alveolar/blood monocytic HLA-DR or CD8⁺ lymphocytes PD-1 expression and hospital mortality.

Conclusions: IL-8 was the most compartmentalized cytokine and lower BAL fluid-to-serum concentration ratios of IL-1Ra were associated with hospital mortality in patients with pneumonia-associated ARDS.

Keywords: Adult; Cytokines; HLA-DR antigens; PD-1; Pneumonia; Respiratory distress syndrome.

Fig. 1

Spearman correlation coefficients of inflammatory cytokines, epithelial/endothelial injury biomarkers (a) and cell surface biomarkers (b) measured in the alveolar (bronchoalveolar lavage (BAL) fluid) and blood compartment. Positive correlations are indicated in red, negative ones in blue

Fig. 2

Bronchoalveolar lavage (BAL) fluid-to-serum concentration ratios (a, b) and BAL fluid-to-blood cells ratio (c, d). ARDS patients (light red) are compared with controls (opened circles) (a, c); ARDS patients with shock (dark blue) are compared with ARDS patients without shock (light blue) (b, d). Symbols indicate median and bars show the 1st and 3rd tertiles. p values come from the Mann–Whitney test; *Concentrations of Serpin, RANTES, IL-7, VEGF and amphiregulin could not be measured in controls; BAL fluid-to-serum concentration ratios of IFN-γ and IL-10 could not be computed because serum concentrations equaled to zero in controls

Fig. 3

HLA-DR⁺ monocytes and T CD8 + PD-1⁺ lymphocytes in bronchoalveolar lavage fluid and blood of patients with pneumonia-related acute respiratory distress syndrome (ARDS) (n = 70) and controls (n = 7). Expression of monocytic HLA-DR was quantified in percentage of positive cells (a) or in mean fluorescence intensity (MFI, b); by two-way ANOVA with repeated measures, there was a significant effect of group (ARDS vs controls, p < 0.0001) and of sample compartment (BAL fluid vs blood, p < 0.0001), with significant interaction (group x compartment, p < 0.0001 in percentage and p = 0.0011 in MFI), on the expression of monocyte HLA-DR. Expression of PD-1 on CD8⁺ lymphocytes was quantified in percentage of positive cells (c) or in mean fluorescence intensity (MFI, d). By two-way ANOVA with repeated measures, there was a significant effect of group (ARDS vs controls, p < 0.001) and of sample compartment (BAL fluid vs blood, p < 0.001), without significant interaction (group × compartment, p = 0.549), when expressed in percentage of positive cells (c). When results were expressed in MFI (d), there was no significant effect of group (ARDS vs control patients, p = 0.252), or of sample compartment (BAL fluid vs blood, p = 0.404), without significant interaction (group × compartment, p = 0.488). Displayed p values come from post hoc comparisons performed using the Sidak’s test. Horizontal bars represent median values