MONOCLONAL IGM ANTIPHOSPHATIDYLSERINE ANTIBODY REACTS AGAINST CYTOSKELETON-LIKE STRUCTURES IN CULTURED HUMAN UMBILICAL-CORD ENDOTHELIAL-CELLS

PROBLEM: It has been proposed that antibodies against phospholipid-dep endent antigens (aPLs), induce recurrent pregnancy loss and thrombosis through modulation of endothelial cell function, yet aPLs have not be en conclusively shown to bind with endothelial cells. METHOD: Using in direct immunofluorescence we investigated the anti-endothelial cell re activity of three monoclonal antibodies that differentiate between the phospholipids cardiolipin (CL) and phosphatidylserine (PS): BA3B5C4 ( CL+/PS+); 3SB9b (CL-/PS+); and D11A4 (CL+/PS-). Cultured umbilical cor d endothelial cells were prepared without fixation or with cold aceton e fixation. RESULTS: None of the aPLs reacted with endothelial cells p repared without fixation. 3SB9B reacted strongly with cytoskeletal-lik e components in acetone-fixed cells, whereas BA3B5C4 and D11A4 were un reactive. The cytoskeletal-like binding of 3SB9b was completely blocke d by a monoclonal antibody against vimentin, whereas antibodies agains t tubulin or actin were not inhibitory. Lipid extraction of the cells destroyed the 3SB9b reactive antigen without affecting the reactivity of anti-vimentin. CONCLUSION: These results suggest that phospholipid- dependent antigenic determinants are not expressed on the surface of r esting endothelial cells but that a PS-dependent antigenic determinant is associated with endothelial cell intermediate filaments.