In a recent study published in the journal Nature Immunology, a team of scientists attempted to understand the etiology of Long Coronavirus Disease (Long-COVID) by using blood samples from patients with and without clear Long-COVID clinical course, and examining immunity to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) through „omics“ approaches and serological tests.
Brief: Long COVID is manifested through T-cell dysregulation, inflammation, and a disorganized adaptive immune response to SARS-CoV-2. Image credit: p.ill.i / Shutterstock
The spread and severity of the coronavirus disease 2019 (COVID-19) pandemic have been brought under control through concerted global efforts to develop vaccines against SARS-CoV-2 and vaccinate large portions of the world’s population. While emerging variants seem to have morbidity and mortality rates not comparable to those of the initial COVID-19 wave, Long-COVID or post-acute sequelae of COVID-19 (PASC) continue to pose a significant health risk, with persistent symptoms such as fatigue, myalgia, dyspnea, and long-term effects on cardiovascular, neurological, and muscular health.
Current studies on Long-COVID suggest that immune dysregulation caused by SARS-CoV-2 infection could be responsible for long-term illnesses. Although 10% or more of SARS-CoV-2 infections result in long COVID, the etiology and pathophysiology continue to be unclear. Furthermore, while the role of T-cells in the pathogenesis and immunity to SARS-CoV-2 is known, the involvement of T-cells in the development of Long-COVID still needs to be fully understood.
About the Study
In the present study, researchers used serological tests and an „omics“ approach to understand and characterize global immunity and specific immunity to SARS-CoV-2 using blood samples from patients with and without clinical manifestations of Long-COVID. Their goal was to identify and characterize the immune features specifically associated with Long-COVID to understand the disease’s pathological mechanisms.
The study employed a serological cytometry time-of-flight assay (CyTOF), plasma proteomics, ribonucleic acid sequencing (RNA), and single-cell RNA sequencing (scRNAseq) to characterize the T-cell phenotype in matched cohorts of COVID-19 patients with long illness and fully recovered patients. Blood samples were taken from a well-characterized cohort of COVID-19 patients at eight months after SARS-CoV-2 infection but before re-infection or COVID-19 vaccination.
Cryopreserved blood samples were analyzed once at the start of the study and after stimulation with SARS-CoV-2 spike proteins to identify anti-SARS-CoV-2 T-cells using cytokine staining. The expression of a variety of effector cells, including interferon-γ, numerous interleukins, tumor necrosis factor (TNF), and cytolytic markers such as perforin and granzyme B, were examined for these T-cells. Manual gating was used to identify specific types of T-cells, such as naive, central memory, transitional memory, effector memory, and stem cell memory T-cells.
The expression levels of CyTOF markers such as human leukocyte antigen-DR-isotype (HLA-DR), cluster of differentiation (CD) 13, CD29, CD38, and CXC 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. Additionally, plasma proteome analyses were conducted to determine if immune regulation and inflammation-associated proteins in the plasma samples of Long-COVID patients were elevated compared to patients without Long-COVID.
The results showed that compared to fully recovered COVID-19 patients, long COVID patients exhibited signs of immunosuppression and systemic inflammation, with a globally different distribution of T-cells indicating persistent immune responses. The cytolytic subgroups also demonstrated gender-specific signals.
Individuals with long COVID had significantly lower frequencies of anti-SARS-CoV-2 CD8+ or cytotoxic T-cells, miscoordinated B and T-cell responses to SARS-CoV-2, increased antibodies to SARS-CoV-2, and a higher frequency of CD4+ or helper T-cells prepared to migrate toward inflamed tissue.
Gender-specific differences were also observed, with female long COVID patients showing lower frequencies of naive helper and cytotoxic T-cells and higher amounts of terminally differentiated effector memory helper cells and cytotoxic T-cells expressing cytolytic markers and homing receptors for inflamed tissue.
The „omics“ approach used in the study cumulatively showed that long COVID patients exhibited significant changes in gene expression not only in CD4+ and CD8+ T-cells but also in B-cells and monocytes; with phenotypic disruptions in helper and cytotoxic T-cells overall and those specific to SARS-CoV-2.
Overall, the results indicated that patients with Long-COVID show significant immune-associated and phenotypic changes in T-cells and other immune cells that could be the mechanistic basis for the persistent and widespread symptoms associated with Long-COVID. Miscommunication or mishap 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.
- Yin, K., Peluso, MJ, Luo, X., Thomas, R., Shin, M., Neidleman, J., Andrew, A., Young, KC, Ma, T., Hoh, R., Anglin, K., Huang, B., Argueta, U., Lopez, M., Valdivieso, D., Asare, K., Deveau, T., Munter, SE, Ibrahim, R. & Ständker, L. (2024). Long COVID is manifested through T-cell dysregulation, inflammation, and a disorganized adaptive immune response to SARS-CoV-2. Nature Immunology. https://doi.org/10.1038/s41590023017246, https://www.nature.com/articles/s41590-023-01724-6