Crosstalk between BMSCs and MCs in mouse models. (A) Confocal microscopy analysis for IgD (green), IgM (red), and CD169 (blue) of the spleen of p53^+/+ and p53^−/− mice shows the expansion of IgM^highIgD^low MZ B cell in p53^−/− mice compared with their wild-type counterpart. In p53^+/+ mice, MZ B cells are not expanded and confined within the MZ (arrows). Upper panel original magnification ×100; lower panel, original magnification ×200. (B) Representative flow cytometry analysis showing the increased accumulation of CD21/35^highIgM^high in the spleen of p53^−/− mice. The complete gating strategy is shown in supplemental Figure 6. (C) Cumulative data showing the increased percentage of MZ B cells in the spleens from p53^−/− mice if compared with p53^+/+ mice. (D) Confocal microscopy analysis for tryptase (green), IgM (red), and CD29 (blue) performed in the spleen of p53^+/+ and p53^−/− mice. Representative pictures are shown. In the spleen of p53^−/− mice, tryptase⁺ MCs make contact with CD29⁺ mesenchymal cells. This interaction does not occur within the spleens of wild-type mice. Original magnification ×400. (E) Confocal microscopy analysis showing the expression of CD40 in the spleen of p53^+/+ and p53^−/− mice. In wild-type mice, CD40 (green) expression is restricted to the follicular area. In the spleen of p53^−/− mice, CD40 is also expressed by mesenchymal CD29⁺ (red) cells outside the follicular area, which take contact with tryptase⁺ MCs (blue). Original magnification ×200. (F) TNF production was measured by ELISA in supernatants obtained from BM-MSC and MC cocultures. In this experiment, wild-type or CD40L^−/− MCs were treated with 100 ng/mL LPS for 4 hours, washed, and than added to a monolayer of BM mesenchymal SCs for 24 hours. Each bar, untreated (black bars) or stimulated (white bars), represents the mean ± standard deviation of 2 independent cocultures.