HO-1 expression in oral AIDS-KS tissue.Paraffin-embedded biopsy tissues from oral AIDS-KS lesions were sectioned and mounted on charged slides. The slides were deparaffinized and stained with polyclonal anti-HO-1 and counterstained with hematoxylin/eosin. (A) Rabbit Ig was used as a control for secondary specificity in sections taken from identical tissue blocks. The panel shows low background staining in an area of tumor involvement. Original magnification, × 40. (B) A similar area of tumor involvement from a section derived from the same tissue block shows a high degree of cellularity, numerous abnormal vascular spaces with extravasated erythrocytes, and a marked level of HO-1 expression (dark brown). Original magnification, × 40. (C) HO-1 expression in normal tissue at the tumor margin of the same tissue section shown in panel B. HO-1 was found within the endothelial lining of normal vascular spaces and sporadically in nonvascular regions. Original magnification, × 40. (D) Higher magnification of an area of tumor involvement from the same tissue section shown in panel B showing HO-1 staining in spindle-shaped cells (^*) traversing abnormal, erythrocyte-congested vascular spaces (arrows). Original magnification, × 63.