Pathogenesis of BTK-mediated Hyper-Inflammatory Responses in COVID-19 (RESPOND)

Background: Coronavirus disease 2019 (COVID-19) is an acute respiratory syndrome. It is caused by the SARS-CoV-2 virus. People with severe COVID-19 infection have a hyper-inflammatory response. Bruton tyrosine kinase (BTK) plays a role in the innate immune system. BTK inhibition can be used to target the innate immune system that appears to contribute to mortality. This could be an effective way to help the inflammatory responses in people with COVID-19. Objective: To learn more about the immunologic mechanisms by which BTK inhibition may decrease hyper-inflammatory responses in people with COVID-19. Eligibility: People ages 18 and older in one of the following groups: * They are in the hospital with COVID-19. They will or will not be treated with a BTK inhibitor. * They do not have COVID-19. They are or are not in the hospital. They will be treated with a BTK inhibitor for a reason other than COVID-19. Design: Participants will be screened with a review of their demographic and clinical information. Their medical history will be reviewed. If they have COVID-19, their symptoms will be assessed. Participants will give 3-4 blood samples. These may be taken through a vein. They may also be taken through an existing central venous catheter. Participants may give a stool sample. This will be collected by nursing staff. It will be collected using a stool collection vial. Stool collection is optional. Participants samples will be collected over about 7 days. These will be used for research and genetic testing.