EXPRESSION OF CD59, A HUMAN-COMPLEMENT SYSTEM REGULATORY PROTEIN, IN EXTRAEMBRYONIC MEMBRANES

CD59 (leukocyte cluster of differentiation antigen 59), is a phosphati dylinositol glycan-anchored membrane protein that inhibits lysis of ce lls by terminal complement system components. To further define comple ment regulatory proteins relevant to pregnancy, this study characteriz ed the expression of CD59 in human extraembryonic membranes. Immunohis tology with CD59 monoclonal antibody MEM-43 showed that this molecule was normally present on the apical surface of the syncytiotrophoblast, on extravillous cytotrophoblast, and amniotic epithelium. Immunoblott ing confirmed that first and second trimester syncytiotrophoblast micr ovilli (STM) contained a glycoprotein similar in mass and glycosylatio n to CD59 from adult cells and tissues. Reactivities of STM with MEM-4 3 in ELISA were 2- to 6-fold higher than those of kidney, erythrocyte and platelet membranes. Term placental STM from recurrent spontaneous aborting patients after immunotherapy, reacted with MEM-43 in ELISA si milarly to STM from normal individuals. Plasmas from pregnant women an d umbilical cords had 50% or greater reactivity with MEM-43 than did n ormal plasmas. CD59 could help protect extraembryonic epithelia from d amage by complement in maternal blood and amniotic fluid. The apical l ocation of CD59 reflects the immunological roles and functional polari zation of plasma membranes in the syncytiotrophoblast.