Postdoctoral University of S�o Paulo Ribeirao Preto, Sao Paulo, Brazil
Introduction/Rationale: With the growing number of long COVID cases, it becomes essential to understand how SARS-CoV-2 modulates T-cell responses and contributes to tissue immunopathology. This study aimed to characterize CD4+, CD8+, and Treg T-cell profiles in mice and in patients with long COVID, and to investigate the role of Tregs during infection with the Wuhan and Omicron variants.
Methods: K18-hACE2 mice were infected with SARS-CoV-2 (10³ PFU, Wuhan) and assessed at different time points for histological analysis, immunophenotyping, pulmonary gene expression, and inflammatory mediators. A human cohort with 72 individuals (38 Convalescent Controls and 34 long COVID) underwent clinical evaluation, serum mediator quantification, and ex vivo and antigen-stimulated immunophenotyping. The role of Tregs was further explored through infections with Wuhan and Omicron, assessment of regulatory markers, and transient Treg depletion in FOXP3eGFP/DTR x K18-hACE2 mice.
Results: Mice exhibited persistent histopathological alterations and continuous expression of Spike and NSP16 in lung tissue, accompanied by CD4+ and CD8+ T cells expressing CD44⁺, PD-1⁺, GITR⁺, and TIGIT⁺. In the human cohort, there were no major clinical differences between groups, although some symptoms were more frequent in long COVID. Ex vivo analysis showed reduced CD8+ T cells and CD8+ Tim-3+ T cells in long COVID. In mice, Wuhan infection led to a late increase in FOXP3+ Tregs and regulatory markers, whereas Omicron triggered an earlier Treg response. Treg depletion resulted in weight loss and mortality.
Conclusion: SARS-CoV-2 induces persistent inflammation associated with antigen retention in the lungs of infected mice, while peripheral alterations in humans are more subtle, suggesting underlying tissue-specific mechanisms. Tregs modulate immunopathology in a variant-dependent manner, playing a central role in the host response to the virus.
