Further Investigations of the Effects of Anti-2GP1 Antibodies on Collagen-Induced Platelet Aggregation

Anti-beta-2-glycoprotein 1 (anti-(2)GP1) antibodies are associated with increased thrombotic risk in patients with autoimmune disease. There is conflicting evidence on the effects of anti-(2)GP1 antibodies on platelets, with both enhanced and inhibited aggregation previously reported. However, previous studies did not include isotype antibodies to ensure the observed effects were due to anti-(2)GP1 antibodies. The aims of this study were to (1) investigate the effects of anti-(2)GP1 antibodies on collagen-induced platelet aggregation in parallel with negative control (buffer normal saline) and isotype control antibodies and (2) determine the lupus anticoagulant (LA) activity of anti-(2)GP1 antibodies used. Three animal-derived anti-human-(2)GP1 antibodies (1.25, 2.5, and 5 g/mL) incubated with healthy platelet-rich plasma were activated by collagen (2.5 g/mL). Each anti-(2)GP1 antibody demonstrated the inhibition of aggregation compared to negative control, but not to isotype control. No anti-(2)GP1 antibody demonstrated LA activity, suggesting they were probably nonpathological. This study highlights both negative and isotype control markers are important to validate the effects of anti-(2)GP1 antibodies. Assays to measure anti-domain I-(2)GP1 antibodies are recommended to be used in conjunction with functional measures to further investigate the effects of anti-(2)GP1 antibodies.