In some cases, provocative new research shows, some people — men in particular — succumb because their immune systems are hit by friendly fire. Researchers hope the finding will help them develop targeted therapies for those patients.

In an international study in Science, 10 percent of nearly 1,000 Covid-19 patients who developed life-threatening pneumonia had antibodies that disable key immune system proteins called interferons. These antibodies — known as autoantibodies, because they attack the body itself — weren’t found at all in 663 people with mild or asymptomatic Covid-19 infections. Only four of 1,227 healthy patients had the autoantibodies. The study was led by the Covid Human Genetic Effort, which includes 200 research centers in 40 countries.

“This is one of the most important things we’ve learned about the immune system since the start of the pandemic,” said Dr. Eric Topol, executive vice president for research at Scripps Research in San Diego, who wasn’t involved in the new study. “This is a breakthrough finding.”