What is the function of the protein CD20?

Antibodies directed against the protein CD20, which is expressed by immune cells known as B cells, are used to treat B cell non-Hodgkin lymphoma and rheumatoid arthritis. Despite this, the function of CD20 has not been determined. Now, a team of researchers led by René van Lier, at the Academic Medical Center, The Netherlands, has determined that CD20 has a nonredundant role in generating optimal B cell immune responses by analyzing a patient lacking the protein.

The patient was referred to the Academic Medical Center at four years of age, with a history of intermittent respiratory infections and recurrent bronchopneumonia. Detailed analysis of immune cells from the patient revealed that the B cells lacked CD20 expression due to a mutation in the CD20 gene. These CD20-deficient B cells failed to respond normally to certain stimuli in vitro, specifically those known as T-independent antigens.

Further, vaccination of the patient with a T-independent antigen led to a markedly impaired B cell response. The authors therefore conclude that CD20 has an important role in enabling B cells to respond optimally to T-independent antigens and that absence of this protein causes an immunodeficiency characterized by a reduced capacity to make B cell responses to T-independent antigens.