Why does COVID-19 only attack certain organs? This study has a theory

We all know that COVID-19 primarily attacks the lungs and respiratory system. Additionally, in severe cases, it’s also been shown to target the kidney, liver, heart, and certain areas of the neurological system. Beyond those regions, though, COVID-19 seems to leave the rest of the human body alone.

All of this begs the question of why. Why is COVID-19 only focusing on these organs? New research just published by the American Institute of Physics is the first to start formulating an answer to this puzzle. Researchers theorize that infected lung proteins are spreading only to certain organs, making those bodily areas susceptible to coronavirus attacks.

In total, the study’s authors have identified 59 lung proteins that may “activate” the coronavirus in a specific group of other organs via protein-to-protein interactions. These at-risk areas include the kidney, testicles, heart, cerebral cortex, thymus, and lymph node.

Part of what makes COVID-19’s selective damage so confusing is the apparent fact that it appears to be quite capable of infiltrating pretty much any organ or area of the body.

When the coronavirus infects a new human cell, it does so via a receptor (angiotensin-converting enzyme 2, or ACE2) that can be found pretty much everywhere in our bodies.

“This receptor is ubiquitous in most human organs, such that if the virus is circulating in the body, it can also enter into other organs and affect them,” explains study author Ernesto Estrada from the University of Zaragoza in a release. “However, the virus affects some organs selectively and not all, as expected from these potential mechanisms.”

So, if the coronavirus can enter seemingly any human organ via ACE2, what’s making it only attack a certain group of organs? According to Estrada, the only explanation is that the coronavirus is spreading from organ to organ in a different way.

In search of this hidden transmission route, Estrada focused on the most prominent coronavirus location within the human body: the lungs. More specifically, he investigated the movements of lung proteins throughout the body and their interactions with proteins found in other organs.

“For two proteins to find each other and form an interaction complex, they need to move inside the cell in a subdiffusive way,” he notes.

To better understand what Estrada is getting at with “subdiffusive” movements, imagine the classic video game Frogger. In that game, players must navigate their way around a busy highway and get to the other side without being hit by a car. Similarly, when a lung protein makes its way to another organ (for example, the kidneys) and enters one of its cells, that lung protein must travel through a somewhat treacherous cellular collection of roadblocks on its way to the kidney proteins.

Once the two proteins meet, however, they interact. It’s this interaction that Estrada theorizes may be causing the spread and activation of COVID-19 from the lungs to other organs.

A mathematical model was used to identify 59 lung proteins that appear to interact with and influence other organs. Estrada and his team believe that these 59 proteins, when infected with coronavirus, may set off a chain reaction that spreads the pathogen to other organs.

On an actionable level, researchers hypothesize that neutralizing these lung proteins in COVID-19 patients early on may stop the infection from spreading to other areas of the body like the heart, neurological system, or kidneys.

“Targeting some of these proteins in the lungs with existing drugs will prevent the perturbation of the proteins expressed in organs other than the lungs, avoiding multiorgan failure, which, in many cases, conduces the death of the patient,” Estrada adds.

The full study can be found here, published in Chaos.