# Immunophenotyping of bronchoalveolar lavage and functional impairment in post-COVID syndrome: Insights from a prospective cohort trial

## TL;DR

This study explores lung inflammation and function in post-COVID syndrome patients using bronchoalveolar lavage and imaging.

## Contribution

The study identifies T-helper lymphocytic inflammation in the lungs of post-COVID syndrome patients.

## Key findings

- T-helper lymphocytic inflammation was observed in 19.2% of post-COVID syndrome patients.
- BALF lymphocyte count was linked to reduced lung function and oxygen gradient.
- Persistent HRCT changes were common in post-COVID syndrome patients.

## Abstract

Following recovery from COVID-19, there is evidence for pulmonary sequelae and functional impairment. Data regarding the immunopathological mechanisms are limited. This study aimed to investigate the relationship between bronchoalveolar lavage fluid (BALF) cellularity, lung function impairment and high-resolution computed tomography (HRCT) changes in post-COVID syndrome patients.

Patients with post-COVID syndrome were enrolled in this Austrian single-center prospective observational cohort study. All patients underwent a pulmonary function test (PFT) and chest HRCT. Those with pathological HRCT findings underwent bronchoscopy with BALF sampling for differential cell count and fluorescence-activated cell sorting analysis.

In this study 26 patients with post-COVID syndrome underwent bronchoscopy with BAL. The HRCT showed ground-glass opacifications (69.2%), organizing pneumonia (7.7%) or both (11.5%). The PFT revealed restrictive lung disease in 38.5% and reduced diffusion capacity in 68%, 19.2% showed a pathological BAL cell pattern predominantly consisting of CD4+ T‑cells. The BALF lymphocyte count was associated with reduced forced vital capacity (p = 0.016) and an elevated alveolar-arterial oxygen gradient (p = 0.04).

A notable percentage of patients with post-COVID syndrome with persistent HRCT changes showed T‑helper lymphocytic inflammation in the lungs. The degree of alveolar lymphocytosis was associated with lung function impairment. This could suggest that a prolonged inflammatory response in the alveolar compartment contributes to the pathogenesis of post-COVID syndrome.