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

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Abstract
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.