Study describes pair of genetically equal twins that showed different cellular responses to coronavirus infection

Monozygotic twins are those considered genetically identical. Traditionally, they help scientists to identify which characteristics are most intensely determined by genetics and which are most influenced by each person's experiences. In the middle of the pandemic, an almost natural question would be: how much does genetics influence the way the body's defense system behaves against the coronavirus? A group of Brazilian scientists has already asked this question and has also started looking for the answer: they studied two pairs of identical twins who tested positive for covid-19, but presented different conditions for the disease.

One pair of twins, who are male, had similar results and had no symptoms. The female pair reported symptoms. One of the sisters, a health professional, was reinfected months after the first infection, this time with more intense symptoms. The results of the study describe as deficient the cellular response of the reinfected twin - the cellular response is one of the fronts of action of our immune system, involving mainly cells called T lymphocytes.

"We expected that these people had similar symptoms and even the same outcome, with a similar evolution and disease progression. Other than that, we did not find, at first, in genetics, an answer to these different immune behaviors", says Matheus Vidigal.

But why were there different cell responses between genetically equal individuals? The researchers suggest that the explanation may lie in the construction of immune memory, distanced from genetic factors. According to Matheus Vidigal, one of the authors of the study, the hypothesis is that, throughout life and in the varied experiences involving pathogens and different exposures to antigens, each of the sisters developed different immune responses, even though they were under the same social context. "It is as if our immune response was unique", explains the biologist, who is a postdoctoral fellow at the Center for Studies on Human Genome and Stem Cells at USP (Genome USP).

In addition to the USP Genome, the study was carried out by researchers from Instituto do Coração (Incor) of Hospital das Clínicas (HC) of Faculdade de Medicina da Universidade de São Paulo (FMUSP), Universidade Estadual Paulista (Unesp) and Universidade Federal de São Paulo ( Unifesp). The preprint article (previous version, still without external review), entitled Monozygotic twins discordant for severe clinical recurrence of Covid-19 show drastically distinct T cell responses to SARS-Cov-2, was published in March, on the medRxiv platform, and and counted with 31 scientists, among them professors Jorge Kalil (director of Incor), Mayana Zatz (coordinator of Genome USP) and had the coordination of professor Edecio Cunha-Neto (from the Laboratory of Clinical Immunology and Allergy at FMUSP).

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