Compartmentalized Regulation of Pulmonary and Systemic Inflammation in Critical COVID-19 Patients

Abstract

Critical COVID-19 has been associated with altered patterns of cytokines. Distinct inflammatory processes in systemic and pulmonary sites have been reported, but studies comparing these two sites are still scarce. We aimed to evaluate the profile of pulmonary and systemic cytokines and chemokines in critically ill COVID-19 patients. Levels of cytokines and chemokines were measured in plasma samples and minibronchoalveolar lavage of critical COVID-19 patients within 48 h and 5-8 days after intubation. Distinct inflammatory processes were observed in the lungs and blood, which were regulated separately. Survivor patients showed higher lung cytokine levels including IFN-γ, IL-2, IL-4, G-CSF, and CCL4, while nonsurvivors displayed higher levels in the blood, which included IL-6, CXCL8, CXCL10, CCL2, and CCL4. Furthermore, our findings indicate that high TNF and CXCL8 levels in the mini-BAL were associated with better lung oxygen exchange capacity, whereas high levels of IFN-γ in plasma were associated with worse lung function, as measured using the PaO₂/FiO₂ ratio. These results suggest that a robust and localized inflammatory response in the lungs is protective and associated with survival, whereas a systemic inflammatory response is detrimental and associated with mortality in critical COVID-19.

Keywords: COVID-19; SARS-CoV-2; blood; chemokines; cytokines; inflammation; lung.

Figure 1

Correlation matrix of cytokine levels and laboratory parameters within and between lung and plasma. Cytokines, chemokines, and laboratory parameters were measured in mini-BAL and peripheral plasma on days 1–2 and days 5–8 after intubation (n = 34). Correlations were analyzed using the Spearman’s rank correlation coefficient. Each column represents a single cytokine, and the intensity of the color represents the level of correlation (r) between cytokine pairs. Blue color indicates a positive correlation while red represents a negative correlation. Abbreviations: CRP, C-reactive protein; G-CSF, granulocyte colony-stimulating factor; GM-CSF, granulocyte-macrophage colony-stimulating factor; IFN-γ, interferon γ; IL, interleukin; SOFA, Sequential Organ Failure Assessment; PaO₂/FiO₂, arterial oxygen partial pressure/fractional inspired oxygen; TNF, tumor necrosis factor.

Figure 2

Correlations between cytokines and laboratory data (CRP and lymphocytes), marker of lung injury (PaO₂/FiO₂) and clinical severity score (SOFA). Cytokines were measured in mini-BAL and plasma samples on days 1–2 after intubation and were correlated with CPR, lymphocytes, PaO₂/FiO₂, and SOFA. Mini-BAL and plasma cytokine levels were correlated to CRP (n = 28), lymphocytes count (n = 28), PaO₂/FiO₂ (n = 28), and SOFA (n = 28). Correlations were calculated using the Spearman’s rank correlation. Each line represents a single cytokine, and the intensity of the color represents the level of correlation (r). Blue color indicates a positive correlation while red represents a negative correlation. Significant correlations are indicated by * p < 0.05 or ** p <0.01.

Figure 3

Levels of chemokines in survivor and nonsurvivor group. Chemokines were measured in mini-BAL and plasma up to 48 h on days 1–2 and around day 7 (days 5–8) after intubation. Survivors (gray square): n = 13 (days 1–2) and n = 12 (days 5–8). Nonsurvivors (open triangle): n = 15 (days 1–2) and n = 14 (days 5–8). Differences between groups were analyzed using the Mann–Whitney test and are indicated by * when p < 0.05 and ** when p < 0.01. The black lines represent the median of each group. Outliers were identified using the ROUT method (Q = 1%).

Figure 4

Cytokines/chemokines when PaO₂/FiO₂ < 150 mmHg. Cytokines/chemokines measured in minibronchoalveolar lavage (mini-BAL) and plasma when the PaO₂/FiO₂ (P/F) < 150 mmHg compared with P/F ≥ 150 mmHg up to 48 h on day 1 (days 1–2) and around day 7 (days 5–8) after intubation. P/F < 150 mmHg (gray square): n = 12 (days1–2) and n = 7 (days 5–8). P/F ≥ 150 mmHg (open triangle): n = 16 (days 1–2) and n = 19 (days 5–8). The Mann–Whitney test was used for statistical analysis and was indicated by asterisks (*) when (p < 0.05) and (**) when (p < 0.01). The black lines represent the median of each group. Outliers were identified using the ROUT test (Q = 1%).

Figure 5

Levels of cytokines in survivor and nonsurvivor group. Cytokines were measured in mini-BAL and plasma up to 48 h on the days 1–2 (days 1–2) and around day 7 (days 5–8) after intubation. Survivors: (gray square) n = 13 (days 1–2) and n = 12 (days 5–8). Nonsurvivors (open triangle): n = 15 (days 1–2) and n = 14 (days 5–8). Differences between groups survivors and nonsurvivors on day 1–2 and on day 5–8 were analyzed using the Mann–Whitney test and are indicated by asterisks (*) when statistically significant (p < 0.05). The black lines represent the median of each group. Outliers were identified using the ROUT test (Q = 1%).

Figure 6

Distinct inflammation patterns in lungs and blood are associated with disease outcome in critical COVID-19. Increased levels of inflammatory markers in the lungs of patients with critical COVID-19 associated with survival while increased levels of inflammatory markers in the peripherical blood associates with death.