Light scattering properties and morphologic appearence of CD79⁺TdT⁺ precursors that express or lack CD19. A correlation of the FSC and T-SSC properties of a BM sample stained with CD19, CD79a, and TdT is shown in dot plot A. TdT⁺ precursor cells that express CD79a are depicted in colors: the CD19⁺ subpopulation of these cells is painted green, whereas CD19⁻CD79a⁺TdT⁺ cells appear red. Histograms of the same material, correlating the FSC (B) or the T-SSC (C) in the x-axis with a relative measure of the cell number (y-axis) show only gated TdT⁺CD79a⁺ cells. Note that CD19⁻CD79a⁺TdT⁺cells (red) exhibit comparatively higher FSC and SSC properties than the majority of CD19⁺ precursors (green). To study the morphology of these subsets, the same sample was stained with CD10, CD19, and CD34, and the CD10⁺CD34⁺ cells were sorted into a CD19⁺ and a CD19⁻fraction. CD10 and CD34 were used as surrogate antigens substituting for CD79a and TdT to avoid cellular alterations by the fixation/permeabilization reagents (the correspondance of these markers was proven in parallel experiments). Pappenheim-stained cytospin preparations of sorted cells are shown in (D; CD19⁺subset) and (E; CD19⁻ subset). Note that the majority of CD19⁺ precursors are small lymphoid cells, whereas CD19⁻ precursors are intermediately sized blasts with large nuclei and prominent nucleoli and display a wider and basophilic cytoplasm with focal juxtanuclear areas of clearing.