Dr Dave Cartland BMedSc MBChB Ex-MRCGP@CartlandDavid
Post from Jay Wilson. A quite superb post and analysis! THIS NEEDS TO GO VIRAL!!!
This paper seeks to answer the question of why some people are developing acute myopericarditis (heart inflammation) after mRNA COVID-19 vaccination. The researchers discovered that T cells — a type of immune cell — can sometimes mistake certain parts of the vaccine’s Spike protein for human heart proteins.
This “mistaken identity” (called molecular mimicry) leads the immune system to attack the heart in some cases. The effect depends on specific T-cell subtypes (cMet⁺ cells) that are drawn to the heart and can cause damage. The study also shows that this autoimmune response can be prevented in mice by blocking cMet — a molecule that helps T cells travel to the heart... For LAYMANS terms, scroll to the very bottom of the overview.👇
Provided below is a section-by-section overview of the paper “Combined Adaptive Immune Mechanisms Mediate Cardiac Injury After COVID-19 Vaccination” (Fanti et al., Circulation, 2025)
ahajournals.org/doi/10.1161/CI…
Background:
mRNA vaccines (Pfizer and Moderna) teach the body to make the SARS-CoV-2 Spike protein, prompting "immunity."
Cases of acute myopericarditis (AMP) — inflammation of the heart muscle and outer lining — have occurred after vaccination, especially in young men.
The cause of these reactions was unclear. Scientists suspected either:
Direct effects (Spike protein made in heart cells),
Or autoimmunity (the immune system reacting to self-proteins that look like Spike).
The study aimed to find specific immune mechanisms responsible.
Methods:
1. Human samples:
29 vaccinated people in Iceland who developed heart inflammation were studied.
11 met strict diagnostic criteria for myocarditis or pericarditis.
Compared with:
Healthy vaccinated controls (no heart issues)
Patients hospitalized with severe COVID-19 (no myocarditis)
2. Animal model:
Male mice (susceptible to myocarditis) were vaccinated with Moderna mRNA-1273.
Later, other groups of mice were given individual Spike protein fragments (peptides) that resembled heart proteins.
3. Analysis tools:
Flow cytometry to identify specific T cells.
Tissue staining and echocardiography to evaluate heart inflammation.
Statistical methods ensured significant results.
Results:
1. mRNA Vaccine Causes Heart Inflammation in Mice
Mice developed heart lesions and inflammation, especially in the right ventricle.
Their blood showed raised troponin (a heart injury marker).
T cells expressing “cMet” increased — these are memory T cells that “home” to the heart.
The vaccine triggered systemic inflammation, increasing HGF (hepatocyte growth factor), which helps imprint these T cells with heart-homing ability.
2. Spike–Heart Protein Similarities Identified
Researchers found three Spike peptides similar to human heart proteins:
1. P87 → similar to myomesin and ion exchangers in muscle.
2. PS5 → similar to a potassium (K⁺) channel called Kv2.1, crucial in heart rhythm.
3. P177 → similar to nebulette, a heart structural protein.
When tested in mice:
cMet⁺ T cells responded strongly to PS5 and P87 (producing inflammatory cytokines like IL-17 and IL-13).
P177 caused minimal response.
Indicates that Spike–Kv2.1 mimicry (PS5 peptide) may drive autoimmunity.
3. Human T-Cell Responses
In humans, T cells from myocarditis patients (but not healthy vaccinated people) reacted to the same Spike epitopes (especially PS5h).
Their T cells produced inflammatory cytokines TNF-α, IL-4, and IL-17, showing a “Th1/Th2-mixed” autoimmune pattern.
COVID-19 patients also had activated T cells but not the same heart-directed cytokine pattern — showing the effect was specific to the vaccine reaction.
4. PS5 Peptide Alone Causes Myocarditis in Mice
When mice were IMMUNIZED INTRANASALLY with the PS5 peptide, they developed heart inflammation and increased cMet⁺ T cells, mimicking vaccine-induced disease.
