Expansion and dissemination of B220+CD43+ B cell progenitors in the Blk(Y495F)-15 transgenic line. Single-cell suspensions were prepared from spleen, lymph nodes, thymus, and bone marrow from lymphomatous Blk(Y495)-15 transgenic mice or from age-matched, nontransgenic littermates. Cells were stained, singly or in combination, with PE- (y axis) or FITC- (x axis) conjugated antibodies to CD19, B220, CD22, IgM, IgD, and CD43 as indicated. The founder, five transgenic progeny, and four normal mice were examined; representative results are presented.