Fas and Fas ligand expression on human peripheral blood leukocytes

Objectives: Study of Fas and Fas ligand (Fas-L) expression, as well as sFas-L release, by fresh human peripheral blood leukocytes. Methods: Flow cytometry, cytotoxicity, immunofluorescence staining of fresh smears, Western blotting. Results: Granulocytes and monocytes express a low level of Fas receptor, but no Fas-L. These cells, as well as NK cells, contain presynthesized depots of Fas-L which they express following activation by brief storage (60 min) at room temperature or during separation from whole blood. Such activation also leads to Fas receptor upregulation. NK cells do not express Fas receptor. Once expressed on blood leukocytes, fully functional Fas-L can be released from the membrane and can be detected in plasma-free cell supernatants. Conclusion: Human peripheral blood granulocytes, monocytes and NK cells contain intracellular presynthesized Fas-L which they readily express following blood anticoagulation, blood storage or cell separation. Soluble Fas-L is released from those cells and can be detected in protein-free supernatants by immunoblotting.