Self-renewal of B-1 lymphocytes is dependent on CD19

The B-1 subset of B lymphocytes is maintained by self-renewal of mature cells, and this process may involve signaling through membrane immunoglobulin (mIg). We determined whether CD19, a membrane protein that co-stimulates B cells by mIg, has a role in this process. Pre-natal treatment of mice with 1D3, a rat anti-mouse CD19 monoclonal antibody, down-regulated CD19 expression and reduced by sixfold the number of B-1a cells at birth; B-2 cells were relatively unaffected. Prolonged treatment of adult mice with 1D3 caused the loss of approximately 2% per day of peritoneal B-1a cells, without diminishing the recovery of splenic B-2 cells. The loss of B-1a cells was associated with inhibition of their replication rather than with accelerated turnover. Therefore, CD19 is involved in the development and self-renewal of B-1a cells, perhaps through its ability to amplify signaling through mIgM.