Lupus anticoagulant activities of murine monoclonal antibodies to liposomal phosphatidylinositol phosphate.

Four murine monoclonal antibodies having high levels of activity against phosphatidyl-inositol phosphate (PIP) were tested for lupus anticoagulant activity. The antibodies showed different degrees of potency in a modified partial thromboplastin time test (APTT) that used dilutions of either bovine brain extract (Thrombofax) or liposomes consisting of phosphatidylcholine/phosphatidylserine (PC/PS) as the phospholipid source. The same relative order of anticoagulant potency that was observed in the APTT that used the PC/PS liposomes was maintained when the anti-PIP antibodies were tested for cross-reactivity either by induction of complement-dependent immune damage to liposomes containing PS, or in enzyme-linked immunosorbent assays that used PS, cardiolipin (CL), or phosphatidylinositol (PI) as antigens. The data indicate that monoclonal antibodies to PIP can express anticoagulant activity in a modified APTT that correlates with their different degrees of cross-reactivity against the negatively-charged phospholipids PS, CL, and PI.