B Cell Precursors in Senescent Mice Exhibit Decreased Mitotic Recruitment, Increased Apoptosis, and Altered Expression of Bcl-2 Family Members

. Senescence in inbred strains of mice affects lymphopoiesis within the bone marrow (1,2). In the development of B lineage cells, old age is associated with a significant decline in pre-B cells. This could result from increased cell death (apoptosis) and/or decreased mitotic activity. We have determined the mitotic activity of B cell precursors from aged mice ex vivo and the kinetics of aged pro-B cell proliferation in vitro at the single-cell level in response to IL-7. Furthermore, we have assessed susceptibility of ex vivo aged B cell precursors to apoptosis and expression of the survival molecules Bcl-xL and Bcl-2 and the proapoptotic molecule Baxa in vitro.