Like many scientists during the Covid-19 pandemic, Jill Hollenbach was stumped by why some folks appeared to dodge the worst of the virus while others did not. But as an immunologist at the University of California, San Franciso, she had a hunch about a set of proteins called human leukocyte antigen (or HLA). These proteins dot each and every one of our body’s cells. When a virus slips inside during an infection, our cells use HLAs to display pieces of viral protein to passing immune cells, much like a waiter with a tray of cocktail drinks.
