Notch2IC induces MZ B-cell development despite the absence of CD19. (A) In the spleen, most of Notch2IC-expressing, CD19-deficient B cells adopt a MZ B-cell phenotype. Splenic lymphocytes from mice of the indicated genotypes were analyzed by flow cytometry for the expression of IgM and IgD (top) or CD21 and CD23 (bottom). Numbers indicate mean percentages and SDs of lymphocyte-gated populations of B220⁺ B cells. The plots are pregated on lymphocytes and B220⁺ cells. The right panel is additionally gated on hCD2, displaying the distribution of Notch2IC-expressing cells. Fo B cells (IgM⁺IgD⁺), MZ B and transitional B cells (IgM⁺IgD^low; top); Fo B cells (CD21^intCD23⁺) and MZ B cells (CD21^highCD23^low; bottom). The calculation is based on 3 independent experiments. (B) Notch2IC-expressing, CD19-deficient B cells are located in the MZ. Immunohistochemical staining of splenic cryosections from mice of the indicated genotypes for MOMA-1⁺ metallophilic macrophages (α-MOMA-1; blue), IgM⁺ B cells (α-IgM; red), and CD3⁺ T cells (α-CD3; blue). The MZ is indicated by arrows. Scale bar: 250 μm.