Recap of this post:
Several studies have found that the virus causing COVID-19 can infect different cell types in our immune system and many of these cells then die. This may theoretically lead to immune dysfunction/imbalance. It's too early to know the clinical effects from this now and in the future.
Authorities should be aware of this.
We still don't know the long term impact of this virus for human health. Evidence for SARS-CoV-2 so far, and experience from those affected by SARS1, point to serious long term effects. It would be wise to prevent transmission until we have new and better vaccines and/or more knowledge.
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Technical outline:
SARS-CoV-2 infects models of T lymphocytes, preferably activated CD4+ cells, in vitro, independently of the ACE2 receptor and induces pronounced programmed cell death potentially contributing to the lymphopenia seen in ~80% of hospitalized C19 patients.
Among those tested in this study, after SARS-CoV-2 infection "CD4+ and CD8+ T lymphocytes almost declined to zero in some patients", while B and NK cells were unaffected. Technically: Both Jurkat and M4 (model T cell lines) were infected, in vitro. (This means we don't know for certain if we'd see the same results, had they tested primary (the "real") T cells.)
However, several recent studies have found SARS-CoV-2 infects several immune cell populations: neutrophils, macrophages, monocytes, plasma B cells, T cells, and NK cells. Here, monocytes were infected independently of ACE2, causing systemic inflammation and leading to massive cell death of the infected immune cells:
https://www.nature.com/articles/s41586-022-04702-4
Question: What are the long term implications for human health?
Forbes' take on the first paper: "As research continues to develop, it will be interesting to discover exactly how this virus attacks and dismantles one of our key defense systems."
https://www.forbes.com/sites/williamhaseltine/2022/04/14/sars-cov-2-actively-infects-and-kills-lymphoid-cells/
So what happens over time, and what does this mean?
Here, "Five of 35 cases (14%) had Lymphopenia in the later follow-up range of 80–102 days... subgroup analyses showed that patients with lymphopenia experienced more frequently persistent symptoms"
https://www.nature.com/articles/s41598-021-91270-8
And here too, CD4+ lymphopenia persisted over some time: A decrease in CD4+ T cells "was observed in 60% (9/15), 60% (9/15), and 46.7% (7/15) of total patients at 0, 8, and 16 weeks after discharge, respectively".
In this article, titled "T cell apoptosis characterizes severe Covid-19 disease", the authors write: "Based on our knowledge of HIV pathophysiology, we hypothesized that SARS-CoV-2 infection-mediated lymphopenia could also be related to T cell apoptosis"
If T cells can be infected by SARS-CoV-2 in vivo, leading to apoptosis (apoptosis=programmed cell death), this can explain the findings.
https://www.nature.com/articles/s41418-022-00936-x
Yet another study: Here, they found that lung-resident macrophages (another immune cell population) were infected by SARS-CoV-2, leading to massive death of these macrophages through the related mechanism of pyroptosis. The cells dying prevented further replication of the virus in those cells.
Early in the pandemic, an article reporting infection of Jurkat T cells, similar to the first paper, was retracted due to methodological issues:
1. They were criticized for using model T cells and not the real stuff (but I find it hard to see how that in itself would imply retraction if it weren't for the very sensitive issue) and
2. The flow cytometry methodology was criticized. So unfortunately, it is now not possible to study the details of the retracted article, link here: https://www.nature.com/articles/s41423-020-0424-9 In the first article in this post, this finding is replicated. Still much is unknown, but in sum, it is clear that SARSCoV2 can lead to substantial disturbances in immune cell populations.
This is based on a Twitter thread: https://twitter.com/GANyborg/status/1532377503809019904?s=20&t=00_qZFdPuKiXI0G2_j66uA
The thread can be read here for better overview of the included studies: https://threadreaderapp.com/thread/1532377503809019904.html