High-Dimensional Immunophenotyping of Post-COVID-19 and Post-Influenza Patients Reveals Persistent and Specific Immune Signatures After Acute Respiratory Infection.

Long-term consequences of SARS-CoV-2 infection are unknown since recovered individuals can experience symptoms and latent viral reactivation for months. Indeed, acute post-infection sequelae have also been observed in other respiratory viral infections, including influenza. To characterize post-COVID-19 and post-influenza induced alterations to the cellular immunome, peripheral blood mononuclear cells (PBMCs) were obtained from patients 3 months after recovery from COVID-19 (n = 93) or influenza (n = 25), and from pre-pandemic healthy controls (n = 25). PBMCs were characterized using a 40-plex mass cytometry panel. Principal component analysis (PCA), classification models, and K-means clustering were subsequently applied. PCA identified distinct immune profiles between cohorts, with both post-COVID and post-flu patients displaying an altered chemokine receptor expression compared to pre-pandemic healthy controls. These alterations were more prominent in post-COVID patients since they exhibited highly increased expression of chemokine receptors CXCR3 and CCR6 by various lymphoid populations, while post-influenza patients mainly showed a decrease in CCR4 expression by naïve T cells, monocytes, and conventional dendritic cells. Classification models using immunophenotyping data confirm the three groups, while K-means clustering revealed two subgroups among post-COVID patients, with younger patients showing more pronounced immune alterations in the chemokine receptor profile, independently of long COVID symptoms. In conclusion, post-COVID and post-influenza patients exhibit distinct and unique persistent immune alterations. Understanding these altered immune profiles can guide targeted therapies for post-COVID syndrome and highlight differences in immune recovery from various respiratory infections.