SELF-RENEWAL OF B-1 LYMPHOCYTES IS DEPENDENT ON CD19

The B-1 subset of B lymphocytes is maintained by self-renewal of matur e cells, and this process may involve signaling through membrane immun oglobulin (mIg). We determined whether CD19, a membrane protein that c o-stimulates B cells by mig, has a role in this process. Pre-natal tre atment of mice with 1D3, a rat anti-mouse CD19 monoclonal antibody, do wn-regulated CD19 expression and reduced by sixfold the number of B-1a cells at birth: B-2 cells were relatively unaffected. Prolonged treat ment of adult mice with 1D3 caused the loss of approximately 2% per da y of peritoneal B-1a cells, without diminishing the recovery of spleni c B-2 cells. The loss of B-1a cells was associated with inhibition of their replication rather than with accelerated turnover. Therefore, CD 19 is involved in the development and self-renewal of B-1a cells, perh aps through its ability to amplify signaling through mIgM.