T Cells Lymhopenia in SARS-CoV-2 Infections

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T Cells Lymhopenia in SARS-CoV-2 Infections


 

It’s important that role of T lymphocyts in immunology and pathology of SARS-CoV-2 infection. The dysregulation of the immune response in T lymphocytes is frequently observed (82.1%) in SARS-CoV-2 infection and this may help to increase of severe of COVID-19 symptoms.

Especially including of ICU Covid patitents, a seriously decrease of the number of T & NK cells has been observed. It will be discussed in the future whether this decrease in the number of T and NK cells during COVID infections contributes to the pathogenicity of the SARS-CoV-2 infection or whether the factors causing the pathogenicity are responsible for the decrease in these cell numbers.

In HIV infections, the decrease of number of especially CD4 and NK cells has been observed but CD8 levels either remain normal or are slightly elevated than normal. In SARS-CoV-2 infections, both CD8, CD4 and NK cell levels showed serious decreases. These decreases were more severe compared to HIV patients.


This lymphopenia observed in the acute phase of SARS-CoV-2 infection shows signs of normalization within 6 months and is followed by normalization of functional T cell responses to other viral antigens. However, it is unclear whether T cell lymphopenia and depression will become permanent as a result of frequent re-infections.

 

TNF-a / IL-6 / IL-10 Cytokins in SARS-CoV-2 Infections

In the SARS-CoV-2 patient groups that were followed under observation for a period of time, it was observed that the CD8 and CD4 lymphocytes in the patients expressed the PD-1 and Tim 3 depletion markers at increasing levels throughout the process.

These observations were the first signs of lymphopenia in SARS-CoV-2 infections. In detailed examinations conducted in these patients, it was observed that the secretion of TNF-a, IL-6 and IL-10 cytokines increased and a negative correlation was detected between these immune elements and the level of CD8 and CD4 lymphocytes.

WHAT IS TNF-a

TNF-α is a proinflammatory cytokine that interacts with TNFR-1 on aged T cells, promoting T cell apoptosis or necrosis. This immune component may be one of the mechanisms inducing the observed T cell loss in patients over the age of 60

WHAT IS IL-10

IL-10 is an inhibitory cytokine. It inhibits T cell proliferation and may induce T cell exhaustion. In animal models, blocking IL-10 function has been successful in preventing T cell exhaustion.


SUMMARY

These cytokines can be secreted by macrophages, monocytes, and T cells. However, the recent study indicates that these immune components are not released from T cells during SARS-CoV-2 infection.

A cytokine storm involving such cytokines may contribute to lymphopenia by promoting T cell apoptosis or necrosis.

 

 

 

 



RESOURCES

Fathi N, Rezaei N. Lymphopenia in COVID-19: Therapeutic opportunities. Cell Biol Int. 2020 Sep;44(9):1792-1797. doi: 10.1002/cbin.11403. Epub 2020 Jun 3. PMID: 32458561; PMCID: PMC7283672.

Jafarzadeh A, Jafarzadeh S, Nozari P, Mokhtari P, Nemati M. Lymphopenia an important immunological abnormality in patients with COVID-19: Possible mechanisms. Scand J Immunol. 2021 Feb;93(2):e12967. doi: 10.1111/sji.12967. Epub 2020 Sep 14. PMID: 32875598.

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