In August, Shiv Pillai, an immunologist at Massachusetts General Hospital’s Ragon Institute, examined tissue taken from dead COVID-19 patients.Pillai and co-workers analyzed the spleen and the thoracic lymph nodes, which drain immune cells from the lungs, of 11 people who died from COVID-19, comparing the tissues with those of six age-matched people who died from other causes.Pillai noted that antibodies collected from COVID-19 patients during and soon after infection have few of the telltale mutations that would indicate they have been through germinal centers.
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As only about 25 reinfections have been confirmed worldwide in a pandemic that has infected more than 30 million people, reinfection seems uncommon, but scientists point out that confirming reinfection is no easy task and many cases are missed. The immune system’s battle against COVID-19 is unleashed in several waves.
In many infections, the immune system builds so-called germinal centers in the spleen or lymph nodes to train cells that make antibodies, but the structures fail to develop in some COVID-19 cases. A research team that has autopsied people who died from COVID-19 has now discovered they lack so-called germinal centers, classrooms in the spleen and lymph nodes in which immune cells learn to mount a long-lasting antibody response to a pathogen. “The immune response to SARS-CoV-2 is extremely heterogenous,” she says.
Another type of immune memory involves killer T cells, which attack human cells that have been infected and turned into virus factories. In a study published last month in the journal Cell, researchers examined the lymph nodes of people who had died of COVID-19 and found they lacked structures called germinal centers. If COVID-19 prevents people from forming germinal centers, said Pillai, that could mean people can only produce antibodies for a limited time after infection.