Convalescent plasma therapy for the treatment of COVID-19 virus infection is based on the function of antibodies, tiny proteins created by the immune system, that combat invaders to the body in a variety of ways. Some are capable of neutralizing a virus, while others work by mobilizing a range of other immune cells that fight off disease.

A type of serologic test known as ELISA is used to determine if the blood does actually contain antibodies specific to the virus. Blood is collected from patients who had a PCR test to diagnose their illness as COVID-19. The blood is processed to separate whole blood into serum and red blood cells to determine if the patient’s plasma can be used for convalescent plasma treatment.

Unique components of the virus, known as antigens, are placed in a testing well. Additional antibodies, tagged with a signal, are introduced that can then be measured if antibodies specific to the virus are present.

Once COVID-19 antibodies are confirmed, the donor blood can then be used for convalescent plasma therapy. This type of therapy introduces antibodies that can bind and kill the virus from one person into the blood stream of an infected patient that does not yet have immunity to the virus. The blood is processed through a machine that collects the plasma, a different part of blood than serum, and returns the blood cells to the patient.

For more information on the Mayo-led, federally-sponsored Convalescent Plasma Expanded Access Program, go to https://www.uscovidplasma.org/.

- Discovery's Edge staff and Donna DeSmet, Mayo Clinic medical illustration/animation, April 15, 2020