In a recent study published within the journal Nature Immunology, a team of scientists attempted to grasp the etiology of long coronavirus disease (long COVID) using blood samples from patients with and without clear long COVID clinical trajectories and examining the immunity against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through ‘omics’ approaches and serological assays.

Letter: Long COVID manifests with T cell dysregulation, inflammation and an uncoordinated adaptive immune response to SARS-CoV-2. Image Credit: p.unwell.i / Shutterstock

Background

The spread and severity of the coronavirus disease 2019 (COVID-19) pandemic have been controlled through concerted efforts worldwide to develop vaccines against SARS-CoV-2 and vaccinate large portions of the worldwide population. Emergent variants don’t appear to have morbidity and mortality rates just like those of the initial wave of COVID-19. Nevertheless, long COVID, or post-acute sequelae of COVID-19 (PASC), continues to be a major health concern, with persistent symptoms reminiscent of fatigue, myalgia, dyspnea, and long-term impacts on cardiovascular, neurological, and muscular health.

Recent studies on long COVID indicate that immune perturbations brought on by the SARS-CoV-2 infection might be liable for the long-term conditions. Nevertheless, although 10% or more SARS-CoV-2 infections lead to long COVID, the etiology and pathophysiology proceed to stay unclear. Moreover, while the role of T cells within the pathogenesis of and immunity against SARS-CoV-2 is thought, the involvement of T cells in the event of long COVID is yet to be fully understood.

Concerning the study

In the current study, the researchers used serological assays and an ‘omics’ approach to grasp and characterize global immunity and specific immunity against SARS-CoV-2 using blood samples from patients with and without clinical manifestations of long COVID. They aimed to detect and characterize the immune features specifically related to long COVID to grasp the pathological mechanisms of the disease.

The study used cytometry by time of flight (CyTOF) serological assay, plasma proteomics, ribonucleic acid (RNA) sequencing, and single-cell RNA sequencing (scRNAseq) to characterize the phenotype of T cells in matched cohorts of COVID-19 patients with long COVID and patients who had completely recovered. Blood samples were obtained from a cohort of well-characterized COVID-19 patients eight months after the SARS-CoV-2 infection but before reinfection or COVID-19 vaccination.

Cryopreserved blood samples were analyzed once at baseline and again after they were stimulated using SARS-CoV-2 spike proteins to discover anti-SARS-CoV-2 T-cells using cytokine staining. The expression of a big selection of effector cells, including interferon-γ, quite a few interleukins, tumor necrosis factor (TNF), and cytolytic markers reminiscent of perforin and granzyme B, were assessed for these T cells. Manual gating was used to discover specific kinds of T cells, reminiscent of naive, central memory, translational memory, effector memory, and stem cell memory T cells.

The expression levels of CyTOF markers reminiscent of human leukocyte antigen – DR isotype (HLA-DR), cluster of differentiation (CD) 13, CD29, CD38, and C-X-C chemokine receptor type 4 (CXCR-4), were also evaluated. The overexpression of specific genes involved in carbon dioxide transport and heme synthesis was also analyzed using RNA sequencing and scRNAseq methods. Moreover, plasma proteomic analyses were conducted to find out if immune regulation and inflammation-associated proteins were elevated within the plasma samples of patients with long COVID as in comparison with those without long COVID.

Results

The outcomes showed that in comparison with COVID-19 patients who had fully recovered, long COVID patients showed evidence of immune dysregulation and systemic inflammation, with the distribution of T cells exhibiting global differences indicative of continued immune responses. The cytolytic subsets also showed sex-specific signals.

Individuals with long COVID had a significantly lower frequency of anti-SARS-CoV-2 CD8⁺ or cytotoxic T cells, mis-coordinated B and T-cell responses against SARS-CoV-2, elevated antibodies against SARS-CoV-2, and a better frequency of CD4⁺ or helper T cells able to migrate towards inflamed tissue.

Sex-specific differences were also observed where female patients with long COVID had lower frequencies of naive helper and cytotoxic T cells and better levels of terminally differentiated effector memory helper and cytotoxic T cell expressing cytolytic markers and homing receptors for inflammatory tissue.

The ‘omics’ approach utilized in the study cumulatively indicated that individuals with long COVID showed significant gene expression changes in not only the CD4⁺ and CD8⁺ T cells but in addition in B cells and monocytes, with phenotypic perturbations within the helper and cytotoxic T cells overall and in those specifically against SARS-CoV-2.

Conclusions

Overall, the findings highlighted that patients with long COVID exhibit significant immune-associated changes and phenotypic alterations in T cells and other immune cells that might be the mechanistic basis for the persistent and wide-ranging symptoms related to long COVID. A miscommunication or error in crosstalk between humoral and cellular adaptive immunity involving B and T cells could contribute to inflammation, immune dysregulation, and the clinical symptoms characteristic of long COVID.