Surface expression of complement regulatory proteins, decay-accelerating factor (DAF) and CD59, on cultured human...

To clarify the response of endothelial cells to complement, we studied not only the reaction of endothelial cells against complement lysis sensitivity (CLS) test, but also the expression of complement regulatory proteins by two-color flow cytometric analysis and backscattered scanning immunoelectron microscopic analysis using monoclonal antibodies to decay-accelerating factor (DAF) and/or CD59. Complement activation didn't lead to the cell death of human aortic endothelial cells (HAECs) and human umbilical vein endothelial cells (HUVECs). In control, two-color flow cytometric analysis indicated that HAECs consisted of a single double-positive population for these proteins as well as HUVECs. Then, HUVECs and HAECs after the CLS test resulted in having same distribution by flow cytometry. Moreover, the microscopic analysis showed that DAF or CD59 was expressed with a diffuse distribution. However, DAF on HUVECs and CD59 on HAECs were present at the margin of cell surfaces more than at the other places. These findings suggest that endothelial cells have a defense mechanism for complement activation in vitro by the changes of expression of complement regulatory proteins on the membrane surface, and that the mechanism of HAECs to complement is the same as that of HUVECs.