Thread by @ZdenekVrozina

COVID-19 creates a state of immune dysregulation where the body may lose control over things it normally keeps suppressed - latent viruses, especially herpesviruses, and possibly even dormant cancer cells.
A new study on EBV and CD8 T cells fits into this bigger picture.🧵

The point is not simply that EBV can reactivate during COVID. We already have quite a lot of evidence for that.
In hospitalized patients with acute COVID, EBV reactivation was very common - around 68-73% - and it was seen not only in critical cases, but also in moderate disease.

The authors looked at EBV, CMV, HHV-6A and HHV-6B.

EBV dominated.
CMV and HHV-6B were detected only at low frequencies.
HHV-6A was not detected at all.
So this does not look like just random viral noise. EBV stands out.

The really interesting part is not just EBV DNA in the blood.
It is what was happening to CD8 T cells.
Patients with EBV reactivation did not have dramatically different overall numbers of major lymphocyte populations.

The difference was in the phenotype - the functional state of the T cells.

In EBV-positive patients, CD8 T cells showed signs of weaker antiviral control.
Less CD28,
less CD11a/CD28 co-expression,
more CD57.
That looks like a shift toward a more exhausted or senescent CD8 T-cell profile.

The problem is not simply too few T cells.
It may be that the T cells are no longer in the right functional state to keep latent EBV under control.
And that matters, because EBV is not a passive passenger.

EBV persists for life, mainly in B cells.
Most of the time, the immune system keeps it locked down, especially through CD8 T-cell surveillance.
When that surveillance weakens, EBV can re-enter a more active state.
Not necessarily as a classic acute infection, but as reactivation.

This is where the broader context matters.
EBV has long been linked to autoimmunity, including multiple sclerosis.
In genetically or immunologically susceptible people, EBV may be one of the key triggers or amplifiers of pathological immunity.

So a hypothetical path from COVID to MS does not have to be direct.
It could look more like this -

COVID - immune dysregulation - loss of EBV control - EBV reactivation/altered EBV immunity - higher risk of autoimmune processes.

And latency is not only a viral concept.
Cancer biology has a similar problem - dormancy.

Cancer cells can sometimes survive for years in a sleeping state. They are not clinically visible, but the immune system and tissue environment help keep them restrained.
A major inflammatory hit may disturb that balance.

Recent data suggest that respiratory viral infections - including SARS-CoV-2 - can awaken dormant disseminated breast cancer cells in the lungs in mouse models.

The effect appeared to depend on inflammatory IL-6 signaling and led to metastatic outgrowth.
Human observational data point in the same direction, though they do not prove causality.

So cancer in this discussion is not a random detour.
It belongs to the same framework -

COVID - systemic inflammation/ immune dysregulation - weakened control over what should stay suppressed.

For EBV, that means viral latency.
For cancer, that means cellular dormancy.
Different biology, similar logic.

The study itself does not investigate MS or cancer.
Its contribution is narrower -
acute COVID was associated with frequent EBV reactivation and with a CD8 T-cell phenotype suggesting impaired antiviral control.
That is the mechanistic piece.

This also fits into the Long COVID discussion.
Long COVID probably does not have one single cause.
It may involve a mixture of viral persistence, antigen persistence, autoimmunity, microvascular damage, dysautonomia, latent virus reactivation, disturbed immune surveillance.

EBV may be one part of that puzzle.

Sum:
During acute COVID, EBV reactivation is common, and it is associated with CD8 T-cell changes that may reflect weaker control of latent EBV.

That is not a small detail.
Latent viruses are not just old infections sitting quietly in the archive.
They are active biological relationships that the immune system constantly manages.
When that management fails, they can re-enter the story.

COVID should not always be understood as a simple infection recovery event.
For many patients, it may be an immune-disrupting event that changes surveillance.
And loss of control over latency - EBV, other herpesviruses, and perhaps even dormant cancer cells - may be one route toward longer term consequences.

Stervbo at al., Acute COVID-19 is associated with altered CD8 T-cells indicative of impaired ability to control Epstein–Barr virus reactivation. @szupraha @ZdravkoOnline @adamvojtech86 link.springer.com/article/10.100…