Severe COVID-19 is characterized by the co-occurrence of moderate cytokine inflammation and severe monocyte dysregulation

Abstract

Background: SARS-CoV-2 has been responsible for considerable mortality worldwide, owing in particular to pulmonary failures such as ARDS, but also to other visceral failures and secondary infections. Recent progress in the characterization of the immunological mechanisms that result in severe organ injury led to the emergence of two successive hypotheses simultaneously tested here: hyperinflammation with cytokine storm syndrome or dysregulation of protective immunity resulting in immunosuppression and unrestrained viral dissemination.

Methods: In a prospective observational monocentric study of 134 patients, we analysed a panel of plasma inflammatory and anti-inflammatory cytokines and measured monocyte dysregulation via their membrane expression of HLA-DR. We first compared the results of patients with moderate forms hospitalized in an infectious disease unit with those of patients with severe forms hospitalized in an intensive care unit. In the latter group of patients, we then analysed the differences between the surviving and non-surviving groups and between the groups with or without secondary infections.

Findings: Higher blood IL-6 levels, lower quantitative expression of HLA-DR on blood monocytes and higher IL-6/mHLA-DR ratios were statistically associated with the risk of severe forms of the disease and among the latter with death and the early onset of secondary infections.

Interpretation: The unique immunological profile in patients with severe COVID-19 corresponds to a moderate cytokine inflammation associated with severe monocyte dysregulation. Individuals with major CSS were rare in our cohort of hospitalized patients, especially since the use of corticosteroids, but formed a very severe subgroup of the disease.

Funding: None.

Keywords: HLA-DR; Immunosuppression; Inflammation; Intensive care unit; Monocyte dysregulation; SARS-CoV-2; Secondary infection.

Fig. 1

Flow chart of the study.

Fig. 2

Plasma pro- and anti-inflammatory cytokine levels and monocyte dysregulation are associated in COVID-19 patients with pulmonary involvement, disease severity and mortality. (a) Spearman correlation of plasma levels of IL-6 or mHLA-DR and PaO2/FiO2 ratios on admission in COVID-19 individuals. The black full line and the grey full line represent the best fit linear relationship of data collected during Wave 1 and Wave 2, respectively. The black dotted lines represent the IC95. Evolution of plasma (b) pro-inflammatory cytokine levels or (c) immunosuppression markers over time during ICU hospitalization measured at baseline (D0-3), on D7-10 and until discharge of the patient for recovery (Endpoint) in alive (blue diamond) and deceased patients (red diamond). Grey diamonds represent patients deceased before D7 (n = 4). Grey dotted lines represent means of cytokines in IDU patients at baseline. Each value represents the mean ± SD. Only statistically significant results were indicated (^¤p < 0.05, ^¤¤p < 0.01, versus baseline, Wilcoxon matched pairs test, **p < 0.01, ***p < 0.001, alive patients vs deceased patients, Mann–Whitney U test). Number of cases for each time point, S: Survivors, NS: Non- survivors. Time D0-3 70(S), 21(NS); D7-10 23(S), 17(NS); Endpoint 18(S). PaO2: Patient's oxygen in arterial blood; FiO2: Fraction of the oxygen in the inspired air.

Fig. 3

Severe COVID-19 patients had both cytokine inflammation and monocyte dysregulation. (a) Spearman correlation of HLA-DR expression on monocytes and plasma IL-6 levels (D0-3, D7-10 and Endpoint) in Wave 2 ICU COVID-19 individuals. The full line represents the best fit linear relationship of data. (b) Evolution of IL-6/mHLA-DR ratio over time during ICU hospitalization measured at baseline (D0-3), at D7-10 and until discharge of the patient for recovery (Endpoint) in alive (blue diamond) and deceased patients (red diamond). Grey diamonds represent patients deceased before D7 (n = 4). Grey dotted lines represent the mean of IL-6/mHLA-DR ratio in IDU patients at baseline. Each value represents the mean ± SD. Only statistically significant results were indicated (^¤¤p < 0.01 versus baseline, Wilcoxon matched pairs test, ***p < 0.001, alive patients vs deceased patients, Mann–Whitney U test). Number of cases for each time point, S: Survivors, NS: non survivors. Time D0-3 70(S), 20(NS); D7-10 23(S), 16(NS); Endpoint 18(S).

Fig. 4

Receiver operating characteristic (ROC) curves predicting unfavorable outcome of COVID-19 in ICU patients. Receiver operating characteristic (ROC) curves of (a) mHLA-DR, (b) plasma IL-6 and (c) IL-6/mHLA-DR ratio, obtained at baseline (red) and at D7-10 (blue), predicting unfavorable outcome (death) of COVID-19 in ICU patients. Area under the ROC curve with 95% CI are indicated for each parameter.

Fig. 5

Cytokine inflammation and monocyte dysregulation at admission are more marked in COVID-19 ICU patients who will subsequently suffer from secondary infections. (a) Plasma IL-6 levels, (b) Monocyte HLA-DR membrane expression and (c) IL-6/mHLA-DR ratio were analysed at admission in ICU patients from Wave 1 (black bars) and Wave 2 (grey bars) according to the occurrence of secondary infections acquired during hospitalization. Bar graphs represent mean ± standard deviation (Statistical comparison by Mann-Whitney U test). Wave 2 ICU patients at baseline (d) plasma IL-6 levels, (e) monocyte HLA-DR membrane expression and (f) IL-6/mHLA-DR ratio were detailed according to the onset of secondary infection, defined as early infection (D0-3) or late infection (> D4). Each dot represents an individual value, and mean ± standard deviation are shown (Statistical comparison by Mann-Whitney U test). Dotted line in (e) represents mHLA-DR threshold predicting early secondary infection occurrence. (g) Monocyte membrane expression of human leucocyte antigen–antigen D-related (mHLA-DR) results from individual patients with late secondary infection, represented as dots in the figure, with lines connecting baseline mHLA-DR expression and D7-10 mHLA-DR expression. The time of onset of infection is shown by the grey area in the figure. Horizontal grey dotted lines represent the mean of mHLA-DR expression at D0-3 in ICU patients with early infection. Horizontal red dotted lines represents mHLA-DR threshold predicting early secondary infection occurrence (comparison versus baseline, Wilcoxon matched pairs test).