Scientists capture extraordinary images of SARS-CoV-2 infecting human airway cells

CHAPEL HILL, N.C. — From wearing masks and social distancing, to industry shutdowns and public health policy changes, the coronavirus pandemic has taken a visible toll on the lives and livelihoods of people worldwide. It is hard to imagine how such catastrophic changes could be caused by a virus so small as to be nearly invisible. Nearly invisible, but not quite, as researchers from the UNC School of Medicine show in striking new images of SARS-CoV-2 infecting human respiratory epithelial cells.

The high-powered microscopic images were captured by Dr. Camille Ehre, an assistant professor of pediatrics at the medical school. The work was done in collaboration with the labs of Drs. Ralph Baric and Richard Boucher, also at UNC. The images are featured in the “Images in Clinical Medicine” section of the New England Journal of Medicine. The images are featured in the “Images in Clinical Medicine” section of the New England Journal of Medicine.

SARS-CoV-2 virions
A higher power magnification image shows the structure and density of SARS-CoV-2 virions (red) produced by human airway epithelia. (Image courtesy: Ehre Lab, UNC School of Medicine)

To obtain the images, the researchers infected human bronchial epithelial cells with SARS-CoV-2 in a laboratory setting. They then examined the cells 96 hours later using scanning electron microscopy.

This technique uses a focused beam of electrons to scan the surface of a sample. As the electrons interact with atoms in the sample, the microscope collects this information and converts it into detailed images of the surfaces of cells and other organisms.

SARS-CoV-2 virions (red).
SARS-CoV-2 virions (red). (Image courtesy: Ehre Lab, UNC School of Medicine)

Since images produced by scanning electron microscopy are black and white, color is typically added to highlight certain details. The images were re-colorized by UNC medical student, Cameron Morrison.

The re-colorized images show SARS-CoV-2 as it emerges from infected airway epithelial cells. The hair-like cilia on the surface of these cells are shown in blue. The cilia transport mucus, shown in yellow, from the lung. A higher power magnification of the image shows the structure and density of the SARS-CoV-2 virions, in red, which are produced by the infected cells. Virions are the complete, infectious form of the virus.

The images from the Ehre lab illustrate the incredibly large number of SARS-CoV-2 virions produced and released per cell inside the human respiratory system. Scientists believe that this intense infection of airway epithelial cells by SARS-CoV-2 serves as a source for spread of the infection to other organs throughout the body, as well as to uninfected individuals.

This high viral burden in the upper respiratory tract may also account for the high transmission rate of the virus. From this perspective, the images only add to the already strong case for the use of masks for limiting the spread of coronavirus.