Figure 3.

B cell development in Ig^HEL and sHEL/Ig^HEL mice that overexpress CD19. Representative two-color immunofluorescence staining of B cells from bone marrow (A), blood (B), spleens (C), and peritoneum of littermate pairs (D). B lymphocytes were revealed by B220 or IgM expression. (A) Quadrants delineated by squares indicate the pre–B cell (B220^lo IgM⁻), immature B cell (B220^lo IgM⁺) and mature B cell (B220^hi IgM⁺) compartments, with numbers representing the percentage of cells within quadrants. The gates that define mature B lymphocytes for sHEL/ Ig^HEL mice were different from the gate used for Ig^HEL mice since surface IgM levels are downregulated in sHEL/Ig^HEL mice. (B and C) Quadrants delineated by squares indicate the B cell (B220⁺ IgM⁺) compartments. Spleen cells were also stained for B220 or IgM and counterstained for sHEL binding or I-A expression. (D) The gates used to determine the frequency of the CD5⁺ B220⁺ population and CD5⁻ B220⁺ population of cells for Table I are shown as polygons and squares. Populations of cells lacking surface antigen expression were determined using unreactive monoclonal antibodies as controls. All samples were stained in parallel and analyzed sequentially by flow cytometry with identical instrument settings. Relative fluorescence intensity is shown on a four decade log scale, with 50% log density contour levels. Horizontal dashed lines in some histograms are provided for reference. These results are representative of those obtained with at least five sets of mice. Equivalent results were obtained by using anti-IgM^a antibody instead of anti-IgM antibody.