COVID-19 tends to strike seniors much harder than kids, although infants with the disease face greater likelihood of time in the ICU or even death.

New lung tissue research in the journal Science Advances suggests a possible reason for this pattern, tied directly to how coronavirus infects the body's cells.

Angiotensin-converting enzyme 2,or  ACE2, is a chemical catalyst located on certain organ cells, including those in the lungs. It helps regulate blood pressure. It's also the docking station SARS-CoV-2 uses to infect cells.

Although amounts of ACE2 vary widely within and between people, research shows a broad pattern in which this "entry enzyme" increases with age. It also reveals that infants have more ACE2 than do older children.

Those amounts, and their changes over time, could help explain patterns of disease severity.

"Of course, they're only a few of many, many factors that can influence what happens to an individual once they encapture COVID-19 virus," said lead author Zintis Inde of Harvard University.

The study also finds cells in younger people are more likely to self-destruct when infected with the coronavirus.

"Once the virus infects the cell and begins to replicate itself, puts stress on the infected cell and pushes it towards a sort of threshold, past which it sort of self-destructs," said Inde. 

Some cancer drugs could encourage such cellular suicide in older adults to limit disease progression.

In both cases, more research is needed.