Abstract

Introduction
Findings on cells and cytokines analyses in BAL are poorly described during and after resolution of non-severe COVID-19 pneumonia, that are the objectives of this study 
 
Methods
This study included 54 pts in whom a BAL was performed (04/2020-02/2021) for the diagnosis or follow-up of suspected COVID-19 pneumonia.Cytological and cytokine analyses (IL-1b, IL-6, IL-8, IL-10, TNFa, IFNg, HGF, TGFb) were performed in BAL blinded to the classification of pts into 3 groups: non-COVID (n=20); COVID (n=13) and post-COVID pneumonia (n=24)
 
Results
Total cell counts were not different between groups. % macrophages were similar between non-COVID and COVID groups, while % neutrophils (PN) were higher - although NS in non-COVID and % lymphocytes (Ly) higher in COVID pneumonia (p<0.024). Plasmocytes were observed in 4/13 COVID and in 1/20 of non-COVID BAL (p=0.042). Compared with COVID pneumonia, post-COVID BAL showed lower % PN, but a persistent Ly alveolitis. Alveolar Ly, in COVID/post-COVID groups were mainly of a CD3/CD4-T cell subset. TGFb was not measurable in the 3 groups. IL-10, IFNg and HGF BAL levels were higher in COVID vs non-COVID pneumonia group (p=0.0128, p=0.005, p=0.007). IL-6, IL-8, IL-10, TNFa, IFNg and HGF levels were lower in post-COVID compared to COVID BAL (all p< 0.005). In COVID pts, IL-1b and IL-6 inversely correlated with %Ly in BAL (r=-0.8, p=0.005; r=-0.7, p=0.02, respectively

Conclusion
Lymphocytic alveolitis associated with plasmacytosis is found in non-severe COVID-19 pneumonia. This alveolitis is associated with the presence of IL-6, IL-8, IL-10, TNFa, IFN g and HGF. BAL alveolitis and cytokine levels normalize in post-COVID-19 pneumonia.