FAS LIGAND IS NOT ONLY EXPRESSED IN IMMUNE PRIVILEGED HUMAN ORGANS BUT IS ALSO COEXPRESSED WITH FAS IN VARIOUS EPITHELIAL TISSUES

Aims-To confirm the recent data obtained in mice, showing that the Fas ligand (Fast) is involved in the phenomenon of ((immune privilege))(t he apparent defect of the immune system in specific anatomical sites) and to extend this finding to humans. Methods-The expression of Fast w as analysed in a panel of histologically normal human tissues by rever se transcriptase polymerase chain reaction and Western blotting. The t issues were brain, breast, bone oesophagus, kidney, Liver, lung, lymph node, ovary, pancreas, pituitary gland, prostate, spleen, stomach (an trum and fundus), striated muscle, testis, thyroid, and uterus. These were obtained from patients with various neoplastic and nonneoplastic disorders; placental tissue was obtained after normal obstetric delive ry, and spontaneous or voluntary abortion. Results-Strong Fast express ion was detected in testis and placenta. Fast expression was also dete ctable, although it was seen to a lesser extent, in oesophagus, prosta te, lung, and uterus, which also coexpressed variable amounts of Fas m RNA or protein or both. The other organs tested for Fast expression we re all negative. Conclusions-Fast in humans is expressed predominantly in immune ''sanctuaries'' such as testis and placenta, suggesting tha t, similar to mice, this expression may contribute to the immune privi leged status of these organs, by preventing dangerous inflammatory res ponses. The coexpression of Fast and Fas in particular epithelia sugge sts that the physiological cell turnover of some tissues may be regula ted by the Fas-FasL apoptotic pathway.