# Cytoimmunological Profile of Lower Airways in Post-COVID-19 Syndrome (PCS): Predictive Value of Bronchoalveolar Lavage

## TL;DR

This study shows that specific immune cell patterns in lung fluid can predict long-term lung issues in patients recovering from COVID-19.

## Contribution

The study identifies BAL cytoimmunological markers that predict persistent interstitial lung disease in post-COVID-19 syndrome.

## Key findings

- Higher BAL neutrophil:lymphocyte ratio (NLR) and neutrophil counts are linked to worse outcomes in post-COVID-19 syndrome.
- Elevated CD8+PD1+ lymphocytes and reduced CD4:CD8 ratio correlate with reduced lung function in PCS patients.
- Th17 activity and IL-8 levels are increased in persistent PCS, suggesting their role in lung inflammation.

## Abstract

Background: It has yet to be determined whether the immunocytological profile of the bronchoalveolar lavage (BAL) in respiratory post-COVID syndrome (PCS) reflects the risk of persistent interstitial lung disease (ILD), including pulmonary fibrosis. In this study, we aimed to assess the prognostic value of the BAL cytoimmunologic profile in PCS-related ILD. Materials and Methods: We enrolled 58 non-smoking patients with a history of COVID-19 and new-onset ILD, divided into PCS remission and PCS persistence groups based on clinical data, including repeated computed tomography and pulmonary function tests. We phenotyped BAL major T cell subsets, immune checkpoints (including programmed cell death-1, PD1), and markers of Th1/Th2/Th17 polarization. Results: The PCS groups compared to the control showed increased total cell, lymphocyte, and neutrophil counts and a high BAL neutrophil:lymphocyte ratio (NLR). PCS persistence compared to the controls presented an increased neutrophil count (26 [17–36] vs. 2.6 [1.9–5.4] 103/mL, median [Q1–Q3], p < 0.001) and percentage, BAL NLR (0.77 [0.26–1.63] vs. 0.21 [0.17–0.31], p < 0.0001), CD8+PD1+ cell percentage (43.5 [34–60.5] vs. 24.5 [22–44]%, p = 0.045), and a decreased CD4:CD8 ratio. A high percentage of CD4+CD196+CD183 cells (relevant to Th17 activity, 6.2 [2.0–9.4] vs. 1.2 [0.7–2.7]%, p = 0.02) and increased BAL supernatant elevated IL-8 levels (62.5 [16–243] vs. 10.9 [3.44–32] pg/mL, p = 0.002) were found in the PCS persistence vs. control groups. In the total PCS group, predicted values of Vital Capacity (VC) [16–243] and Diffusing Lung Capacity for CO (DLCO) correlated negatively with BAL NLR; VC correlated negatively with BAL CD8+PD1+; and DLCO correlated positively with the CD4:CD8 ratio. Conclusions: Worse prognosis in PCS is associated with higher BAL NLR, BAL neutrophilia, an elevated percentage of CD8+PD1+ lymphocytes, and a decline in the CD4:CD8 ratio. Th17 cells and IL-8 participate in lung PCS persistence.