Broncho-alveolar inflammation in COVID-19 patients: a correlation with clinical outcome

Pandolfi et al. assess and compare the broncho-alveolar inflammatory environment between COVID-19 patients admitted to Intensive Care Unit (ICU) and Intermediate Medicine Ward (IMW) at two main COVID-19 centers of Italy (located in Pavia/Milan). Inflammatory cell and cytokine analysis of bronchoalveolar lavage (BAL) samples suggest that hyperactivation of innate immune effectors, particularly neutrophil infiltration, contribute to COVID-19 associated alveolitis in severe cases. Furthermore, elevated levels of pro-inflammatory cytokines (IL-6 and 8) correlate with alveolar inflammatory status and patient clinical outcome.  

Research Highlights 

1. ICU patients showed a significant increase in neutrophils, and relatively lower lymphocyte and macrophage levels, compared to IMW patients.  Neutrophil infiltration at alveolar level did not correlate with clinical outcome.   

2. BAL collected from COVID-19 ICU patients revealed extensive cytopathic damage in all cell types, including loss of nuclear & plasma membrane integrity, pseudopodia formation and cytoplasm vacuolization.  Presence of viral particles were also observed in cytopathic epithelial and mononuclear cells.   

3. Pro-inflammatory IL-6 and IL-8 cytokines were significantly higher in BAL samples derived from ICU compared to IMW COVID-19 patients.  Additionally, non-survivors (N=12) had higher IL-6/IL-8 BAL levels compared to survivors (N=16).  

4. Patients treated with steroids had lower BAL IL-6 compared to patients on tocilizumab or antivirals (remdesivir, lopinavir/ritonavir or hydroxychloroquine).   

5. Direct correlation between BAL IL-6/IL-8 and neutrophil count.  In contrast, IL-6/IL-8 levels inversely correlated with percentage of macrophages.  BAL IL-8 also inversely correlated with lymphocyte count.   

Impact for COVID-19 research:  

• Increased IL-6 and IL-8 levels in broncho-alveolar environment of COVID-19 patients correlates with neutrophil infiltration and is associated with clinical outcome. Steroid treatment could reduce IL-6 levels in severe COVID-19 cases, potentially leading to better outcome.  

Methodologies: 

• Study Type: Patient cohort  

• Key Techniques: Assessment of BAL cell differentials, ultrastructural cell analysis and cytokine profiling  

Limitations: 

• Small patient cohort (N=33; 28 ICU and 5 IMW). Majority of patients were male.  

• Small sample size limited the possibility of additional analysis (e.g. flow cytometric evaluation cell surface activation markers).  

• The study is specific to a particular time & place and cannot be generalised.  

• Paired assessment of inflammatory cytokines in peripheral blood was not possible due to lack of stored serum samples from acute COVID-19 patients/healthy donors.  

• Pre-existing comorbidities may have influenced cellular infiltration and cytokine levels.