Expression of EphA4 in PTLD biopsies. Paraffin-embedded PTLD and tonsils sections were subjected to IHC assays, and hematoxylin was used for the nuclear counterstaining. Positive signals of EphA4 were indicated as a brown color in tonsil biopsies but not in PTLD biopsies. LMP1 expression was also detected as a brown color by IHC assay in PTLD biopsies. The nuclei of the cells are colored blue. Magnification, ×200 (scale bar, 50 µm).