Seeing sick faces may prime the immune system to repel invaders

Our brains might prime our immune system merely by seeing someone who looks sick.

A study published July 28 in Nature Neuroscience found that participants who saw sick-looking faces in virtual reality showed changes in brain activity related to personal space monitoring and threat detection. Additionally, the activity of certain immune cells in the blood increased.

The study is “unique in demonstrating that people’s immune system can be primed just by the visual recognition that someone looks sick,” says Michael Irwin, a psychoneuroimmunologist at UCLA who was not involved in the work. “That’s really remarkable.”

In the study, 248 participants watched humanlike faces approach them in virtual reality. Some avatars displayed clear signs of sickness, such as coughing or rashes, while others appeared fearful or neutral. Those who saw sick-looking avatars appear to enter their personal space reacted faster to their face being touched, suggesting a state of high alert, the team found.

Brain imaging revealed that regions responsible for monitoring personal space reacted differently to sick faces compared with neutral or fearful ones. The salience network, a brain circuit that detects important events in the environment, was also activated. “These two systems were activated differently by a sick avatar,” says Andrea Serino, a neuroscientist at the University of Lausanne in Switzerland, “different even to a fearful avatar.” That suggests the differences were about infection, not threats in general, he says.

Most striking, blood tests revealed that participants who saw sick faces showed increased activity of innate lymphoid cells. These cells, one of the immune system’s first responders, sound the alarm to other immune cells. “This is a completely new level of immune activation I wouldn’t have expected … without entry of a pathogen into the body,” says Camilla Jandus, an immunologist at the University of Geneva.

To show that these changes resembled responses to actual infections, Serino, Jandus and their colleagues compared the changes to responses to a flu vaccine. “The pattern of [innate lymphoid cell] activation for the vaccine was similar to participants exposed to infectious avatars,” Jandus says.

The brain circuits involved may influence the immune system via the hypothalamic-pituitary-adrenal axis, a network of brain regions and glands that controls stress responses. “We show that the hypothalamus increases connection with the salience network during infection [threats],” Serino says.

The discovery could eventually have practical applications, such as improving vaccine responses or the efficacy of certain drugs. “If you have flu and take paracetamol, for instance, you could use virtual reality to boost the effect by modulating the immune system reaction,” Serino says.

This is a long way off, as researchers need a fuller understanding of what’s going on. The team measured only two immune cell types: innate lymphoid cells and another type of white blood cell called natural killer cells, which didn’t change.

The immune system is immensely complex, so a lot remains unknown. “The analysis of the immune response is fairly rudimentary,” says Filip Swirski, an immunologist at Icahn School of Medicine at Mount Sinai in New York City who was not involved in the study. “A lot more should be done to look at this more thoroughly.”

The researchers are already working on this. For instance, they’re looking at whether the effects persist over hours and days — not just immediately after seeing a sick face — and plan to monitor more cells and molecules.

The study also focused only on young adults, so how well the findings generalize to older people remains to be seen. “I’d imagine there’s tremendous biological variability between ages, sexes and probably ethnicity,” Irwin says. “All those factors need to be taken into account.”