Corona vaccination: Body builds up immune memory in organs

16.10.2023 18:09

A vaccination in the upper arm – and the whole body is protected. How does it work? On the one hand, the immune system produces antibodies and cells that patrol the blood throughout the entire organism. On the other hand, as a current study by the Charité - Universitätsmedizin Berlin shows using the example of corona mRNA vaccines, the body builds up a local immune memory in various organs. According to the work published in the Journal of Clinical Investigation [1], immune memory cells are more numerous in organs than in the blood and have enhanced antiviral defense functions.

The researchers had suspected it: findings from animal models have been indicating for some time that most immune memory cells do not circulate in the blood after an infection, but rather become resident in the organs and protect them locally. It is assumed that this also happens after a vaccination. However, proving this in humans is not trivial. “For this you need tissue from many people with a known and comparable vaccination history who, if possible, have never been infected by the pathogen,” explains Prof. Dr. Katja Kotsch, head of the study from the Clinic for General and Visceral Surgery at the Charité. The corona pandemic with many vaccinations carried out now made it possible to obtain the necessary samples.

Memory cells in the liver, kidneys and lungs

For the study, the researchers examined tissue from different organs that was obtained during medically necessary operations, for example to remove a tumor. The samples came from 61 people who had been vaccinated against the coronavirus two to three times with an mRNA vaccine a few months before the operation, independently of the operation, but the majority had not yet undergone the infection.

By specifically stimulating and staining immune cells, the research team was able to detect so-called CD4-positive T helper cells that were directed against SARS-CoV-2 in several tissues. These immune memory cells ensure that other immune cells produce suitable antibodies against the pathogen as soon as it is detected in the body. They also probably help fight the virus directly.

The scientists found the immune memory cells not only in the spleen and bone marrow, tissues in which immune cells mature or are produced by default, but also in the liver, kidneys and lungs. “These data confirm our assumption that after a vaccination, the body creates an immune memory that is stable for months, even in tissues that are far away from the injection site,” says Dr. Arne Sattler, immunologist in Prof. Kotsch's team. Together with her, he is the corresponding author of the study. “We have now shown this for the mRNA vaccines against the coronavirus, but we assume that similar processes also take place after other vaccinations. However, the evidence for this is still lacking and further studies are needed.”

Organ immune memory is created largely independent of age

A comparison with blood samples from the patients showed that significantly more immune memory cells settled in the kidneys, liver and lungs than patrolled through the blood. The messenger substances that the organ cells released also suggested particularly pronounced antiviral properties. Dr. Sattler sums up: “Our data shows that the immune memory in the organs is functionally superior to that in the blood. What this means exactly for the immune protection of the organs is not easy to determine because the exact protective effect of individual immune cells in humans cannot be determined well. However, observations in animal models indicate that such locally anchored, potent T cells can better defend against pathogens.”

And there was another difference between the immune memory in the organs and the blood: the number of protective immune cells that settled in the organs was similarly high, regardless of the age of the vaccinated person. In contrast, fewer immune memory cells circulated in the blood of older patients than younger patients. “In old people, after the corona vaccination, the body creates a numerically similar immune memory in the organs as in young people,” says Prof. Kotsch. “According to our data, the memory cells found in the organs last at least several months. Whether the immune memory remains stable in the tissue over years is the subject of further investigation.”

Original publication

[1] Proß V, Sattler A, Lukassen S et al. SARS-CoV2 mRNA-vaccination-induced immunological memory in human non-lymphoid and lymphoid tissues. JCI 2023 Oct 10. doi: 10.1172/JCI171797