Diverse Defenders

A burning question in COVID-19 research is, why do some people become severely ill while others have only mild symptoms or none at all? While studying the lungs of people as they battle SARS-CoV-2 infection might provide answers, it’s practically and ethically impossible. Researchers have therefore turned to mice, transplanting human lung tissue and immune cells into the animals before infecting them with the virus and tracking the disease. Such humanised mice have enabled researchers to conclude that the severity of infection is, at least in part, down to the variety of macrophages entering the lungs. The image shows a human macrophage containing and surrounded by SARS-CoV-2 particles (green) in one of the humanised mouse lungs. Accumulation of both pro-inflammatory and non-inflammatory macrophages in the lungs was key to ensuring a swift response to the virus while preventing the sort of out-of-control inflammation that’s associated with severe COVID-19 in humans.

Written by Ruth Williams

Ruth Williams

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Ruth is a freelance science journalist based in the US. She's a regular correspondent for The Scientist, and her work has appeared in The Lancet, Nature, Scientific American Mind, BBC Focus and elsewhere. Twitter @rooph

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• Picture courtesy of F Douam and D J Kenney, taken in collaboration with the Harvard Medical School Electron Microscopy Facility
• Department of Microbiology, Boston University School of Medicine, Boston, MA, USA
• Image originally published with a Creative Commons Attribution 4.0 International (CC BY 4.0)
• Research published in Cell Reports, April 2022