Introduction. It has yet to be determined whether the immunologic pro?le of the bronchoalveolar lavage (BAL) in post-COVID-syndrome (PCS) may reflect the risk of pulmonary fibrosis.

The aim of the study was to evaluate the prognostic value of BAL cytoimmunology pattern in  PCS-related interstitial lung disease.

Methods. BAL was harvested from 35 patients with interstitial lung patology who met PCS criteria (all nonsmokers, 12-52 weeks after the end of acute illness). BAL lymphocytes were immunotyped for major T cell subsets, immune check points and markers of Th1/2/17 immune polarization (including CD4/CD196/194/183 typing and BAL supernatant ELISA assays for interferon gamma, IL-5 and IL-17).

Results. High BAL cell count, elevated number and percentage of lymphocytes and neutrophils, low CD4/CD8 ratio and high BAL neutrophil to lymphocyte (Ne/Li) ratio, were found in PCS as compared to controls. Diffusing capacity for CO correlated negatively with BAL CD8+ percentage (rs=-0.55, p<0.001) and Ne/Li ratio (rs=-0.51, p<0.0001). PCS duration was correlated with decreased total number of lymophocytes, but not neutrophils. No differences were found in immune profile of PCS related to different COVID-19 waves. Higher NK percentage, CD8 percentage, increased CD4+CD196+ expression (relevant to Th17 activity) and increased BAL supernatant elevated Il-17 level were found in subgroup of patients (n=8) with persistent PCS (without regression within three months of observation).

Conslusions. High number/percentage of CD8 cells as well as increased activity of Th17 cells predict worse course of PCS with lung interstitial pathology.