Human B-cell development in NSγ mice. Human B-cell development within spleens was characterized in NSγ mice. Four weeks after transplantation, the human CD19⁺ cells did not express any significant surface IgM, IgD, or IgG (panels A,F; n = 6). Twelve weeks after transplantation, the human CD19⁺ cells coexpressed IgM and IgD; however, surface IgG was not expressed (panels B,G; n = 5). At 19 weeks after transplantation, the human CD19⁺ cells also coexpressed IgM and IgD; but surface IgG was not expressed (panels C,H; n = 7). In control samples, CD19⁺ B cells from CB contain subpopulations that coexpress IgM and IgD (D), but also contain cells that express IgG (I, see arrow). The CD19⁺ human B cells within NSγ spleens coexpress intermediate to high levels of CD24 and CD38 at both 12 (not shown) and 19 weeks after transplantation (E). CD19⁺ CB cells contain immature CD24⁺ CD38⁺ B subsets of cells, but also contain CD38^br CD24^neg B cells that are presumably mature (J, see arrow). In each panel, total murine spleen cell preparations were initially gated to examine human CD45⁺ CD19⁺ cells that did not express murine CD45 (not shown). In control panels, total CB cell preparations were similarly gated to examine CD45⁺ CD19⁺ cells (not shown).