Polyfunctional properties of hybridoma lupus anticoagulant antibodies.

Lupus anticoagulant antibodies are antiphospholipid antibodies which are characterized by their ability to prolong the clotting time in in vitro coagulation assays measuring the partial thromboplastin time (PTT). In our study, we have analyzed 11 hybridoma lupus anticoagulant antibodies and studied their reactivity with hexagonal and lamellar phospholipids, DNA, IgG, cytoskeletal components, and intact platelets. Our results demonstrate that hexagonal phase phospholipids but not lamellar phospholipids were able to neutralize the lupus anticoagulant activity of all 11 hybridoma antibodies. However, the lupus anticoagulant antibodies differed from one another in their reactivity with DNA, the Fc fragment of IgG, cytoskeletal proteins and platelets. Some of the lupus anticoagulant antibodies reacted with all of these structures, while others reacted with only some or none of the antigens tested. Isoelectric focusing gel analysis confirmed that this polyreactivity was due to a single antibody. Direct binding of lupus anticoagulant antibodies to intact platelets was shown to correlate with the DNA binding activity of the antibodies. Lupus anticoagulant antibodies were also capable of inducing a morphological shape change in platelets. Our data suggest that hybridoma lupus anticoagulant antibodies may react as lupus anticoagulant antibodies only, anti-DNA antibodies, rheumatoid factors, anticytoskeletal antibodies, and antiplatelet antibodies. The degree of overlap in these subgroups and the epitopes responsible for these multiple reactivities remain to be determined.