Regulation of cell survival during B lymphopoiesis: increased pre-B cell apoptosis in CD24-transgenic mouse bone marrow

CD24 (heat-stable antigen) is expressed in a developmentally regulated fash ion by B cell precursors in mouse bone marrow (BM), but its role in B lymph opoiesis remains obscure. A slight overexpression of CD24 in transgenic (Tg ) mice reads to depletion of B lymphoid cells in BM. The present study exam ines whether CD24 is involved in apoptotic selection of B lineage cells und er normal microenvironmental conditions in vivo. Double immunofluorescence labeling and flow cytometry have been used to quantitate the apoptotic rate s of phenotypically defined B cell populations in BM of CD24-Tg mice. Apopt osis of pre-B cells expressing cytoplasmic mu heavy chains of IgM but lacki ng surface (s)IgM was increased both ex vivo and in short-term culture, whi le the number of pre-B cells was halved compared to BM of normal mice. In c ontrast, B220(+)mu(-) pro-B cells and sIgM(+) B lymphocytes showed no signi ficant change in either apoptosis or number. The findings provide evidence that CD24 can play a role in vivo in modulating pre-B cell apoptosis, a qua lity control checkpoint in B cell development.