PROTECTION OF RAT ENDOTHELIAL-CELLS FROM PRIMATE COMPLEMENT-MEDIATED LYSIS BY EXPRESSION OF HUMAN CD59 AND OR DECAY-ACCELERATING FACTOR/

The present study analyzed the ability of human decay-accelerating fac tor (DAF) and CD59 to protect rat endothelial cell (EC) clones from hu man and primate complement-mediated lysis. By flow cytometry and Scatc hard analysis, we show that human DAF and/or CD59 cDNAs under the tran scriptional control of elongation factor 1-alpha promoter were express ed at levels similar to or higher than that of a human EC line. Human DAF and CD59 were released from the surface of transfected rat cells b y phosphatidylinositol phospholipase C, demonstrating that the two mol ecules were linked to the cell membrane by means of a glycolipid ancho r. The functional activity of the two human C regulatory proteins expr essed on rat EC lines was studied using an in vitro assay of C-depende nt cytotoxic in which rat EC were incubated with human or nonhuman pri mate sera as sources of xenogeneic natural antibodies and C. We demons trate that human and monkey xenogeneic natural antibodies bind to rat cells and induce lysis by a C-dependent mechanism involving mainly the C direct activation pathway. Our data indicate that human DAF and CD5 9, expressed either alone or in combination, abrogated all EC cytotoxi city, even in the presence of 50% human serum. This protective phenoty pe was correlated with decreased membrane attack complex (CD59 and/or DAF transfectants) and C3 deposition (DAF transfectants) on EC surface . Antibodies against the transfected molecules abolished the protectio n against C-mediated lysis.