B lymphocyte deficit in recipients of Mpl^+/+p300^Plt6/Plt6 bone marrow. (A) Flow cytometry plots of bone marrow, lymph node, and spleen cells from recipients of Mpl^+/+p300^Plt6/Plt6 (Plt6/Plt6) and Mpl^+/+p300^+/+ control (+/+) bone marrow stained with antibodies to B220 and IgM showing reduced proportions of B220⁺ cells, including IgM⁺ B cells in each tissue (percentages of cells in specific quadrants is shown). (B) Percentages of B220⁺ cells in bone marrow (BM), spleen (spl), mesenteric lymph node (LN), and blood of recipients of Mpl^+/+p300^Plt6/Plt6 (6/6) and Mpl^+/+p300^+/+ control (+/+) bone marrow. Means plus or minus SD are shown. *P < .05 for comparison of data from recipients of Mpl^+/+p300^Plt6/Plt6 marrow with that of Mpl^+/+p300^+/+ marrow recipients. n = 4 mice per genotype.