S. flexneri interacts with B lymphocytes and induces B cell apoptosis upon natural infection. Representative fluorescence microscopy images of ILFs in colonic biopsy tissue slides from two patients presenting severe shigellosis are shown. Bacteria were stained with an antibody against IpaD (red), B cells with anti-CD20cy (green), and apoptotic cells with a TUNEL kit (gray). Orthogonal slices are shown for each confocal image. Bars, 2 µm.