HP and COVID-19: In 2021, a US multidisciplinary team led by pediatric pulmonologist Yonker teamed up with Alessio Fasano, the pediatric gastroenterologist and researcher who discovered zonulin, the protein responsible for regulating intestinal tight junctions (TJs), published a study on the mechanisms that could be responsible for MIS-C, a rare and sometimes fatal post-COVID-19 complication.