Immunohistochemical analysis of Fas ligand expression in normal human tissues

Cross-linking of Fas and Fas ligand (FasL) induces apoptosis in Fas-bearing cells and regulates apoptosis. Fas is widely expressed in normal human tis sues, but Fast expression has been considered to be restricted to lymphoid tissues. Recent studies have demonstrated that Fast is also expressed in so me nonlymphoid tissues. To screen the in situ expression of Fast in normal human tissues, immunohistochemistry was performed using paraffin-embedded h uman tissues. Fast immunostaining was easily detected in testis, neurons, t rophoblasts, tonsil, lymph node, Paneth cells, hepatocytes, renal tubular e pithelium and bronchial epithelium, consistent with previous reports. Surpr isingly, Fast was also expressed in many other cell types, including thymic medulla, skeletal muscle, cardiac muscle, pituitary gland, parathyroid gla nd, prostate glands, oocytes, epithelium of fallopian tube, endometrial gla nds, and gastric parietal cells. These findings demonstrate that Fast is wi dely expressed in human tissues and suggest that wide but cell-type specifi c expression of Fast may not only be implicated in the regulation of immune homeostasis but also in the regulation of cell death and life in many cell types in vivo.