The in vivo infusion of CD48 MoAb in irradiated recipients of congenic BM shifts BM and splenic populations toward a CD48^low or CD48^neg phenotype. Single-cell suspensions of BM (A) or spleen (B) were obtained from mice undergoing congenic BMT from the experiment shown in Tables 4 and 5 on days 10, 14, and 20 post-BMT as listed. Mice received irrelevant MoAb or CD2 + 48 MoAb according to the regimen listed in Fig 1. Cells were stained for CD48 expression and then analyzed by fluorescence-activated cell sorting (FACS). Isotype-matched control MoAb was used to set gates. For BM (A), CD48 expression was segregated into three antigen density levels. The percent of cells falling within each antigen density level is listed. The isotype-matched control MoAb is shown in the thin line and the CD48 MoAb staining in the heavy line. A representative overlay histogram from three individually analyzed mice per group and a non-BMT control analyzed at each time point are shown. The percentages indicate the percent positive cells in the gate shown.