Detection of proliferating B cells and autoantigen within PLNs of ITP spleens. Sections from (A) 2 ITP spleens and (B) 1 control were stained for CD20 (red), Ki67 (green), or GPIIb/IIIa (green) and assessed for the presence of proliferating B cells and B cells in proximity to GPIIb/IIIa. Visualization was carried out with a Zeiss Axio Imager Z1 fluorescence microscope (×200 magnification).