Detection of IgA⁺ plasmablasts and plasma cells, but not CD20⁺ cells within human mucosal biopsies during RTX treatment. Three patients with diffuse large B-cell lymphoma were treated with RTX plus cyclophosphamide, hydroxydaunomycin, Oncovin, prednisone, and control biopsies were taken after 3 months from the duodenum or stomach. A representative duodenal biopsy is shown with absence of CD20⁺ B cells, whereas numerous CD79a, MUM1, and IgA⁺ cells were detected. Virtually all cells that were stained by these markers showed plasma cell morphology, including IgA⁺/Ki67⁺ plasmablasts detectable at a low frequency (white arrow). Original magnifications, ×200 (top) and ×400 (bottom). Black bar indicates 100 μm; white bar, 50 μm. Microscope was Olympus AX70 and AxioImager Z1 (Zeiss); numeric aperture of objective lenses were ×20, 0.70 mm; ×40, 0.90 mm. Stains used were immunoperoxide, Alexa Fluor 488/555, and DAPI (4′-6′-diamidine-2-phenylindole). Camera used was JVC KY-F70 and CCD camera (AxioCam MRm; Zeiss); acquisition software was DISKUS and Axiovision (Zeiss); and software used for image processing was Adobe Photoshop 7.0 (Adobe Systems).