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anticardiolipin antibodies ; lupus anticoagulant ; monoclonal antibodies ; anti[beta]2glicoprotein I antibodies
Abstract:
Antiphospholipid antibodies are directed against proteins (mostly B2- glycoprotein I and prothrombin) forming complexes with negatively charged phospholipids. Association of antiphospholipid antibodies (LA and/or aCL and/or aB2GPI) with characteristic clinical symptoms (thrombosis and obstretical complications) forms the criteria of antiphospholipid syndrome. The presence of antiphospholipid antibodies is detected by means of two independent methods, coagulometric (LA) and immunoenzymatic (aCL and/or aB2GPI). According to guidelines published in 2006, aPL antibodies are considered as classification criteria for APS, as long as they are determined using standardized methods, i.e. based on recognized calibrators for aCL and aB2GPI, and according to ISTH Standardization Subcommittee in case of LA. The purpose of the present study was to assess the usefulness of monoclonal antibodies (23H9 and 28F4 for LA, and HCAL and EY2C9 for aCL and afB2GPI, respectively) as standards for antiphospholipid antibodies detection methods. The interaction between mouse antibodies against human B2-glycoprotein I (23H9) and human prothrombin (28F4), possessing the properties of lupus anticoagulant was analyzed in 24 human plasma samples. B2GPI-dependent LA effect observed in phospholipid-dependent coagulation assays differed markedly from LA associated with the presence of antibod ; ies against prothrombin. PIT LA turned out to be the most sensitive screening test for LA; dilute Russell Viper Venom Time (DVV) was found to be somewhat less sensitive. Mouse humanized antibodies against human aB2GPI (HCAL and EY2C9; "Sapporo standards") were used as reference calibrators in comparison to in-house standards (serum from patients with known high antibody titer) to establish a cut-off point for positive values in healthy controls. They were also used for assessing intralaboratory reproducibility for aCL determination method. Ninety-ninth percentile values calculated for both aCL and aB2GPI with the use of in-house standard and with monoclonal antibodies were very similar. Moreover, no significant difference was observed while classifying the results as positive or negative; a very important finding for establishing the proper diagnosis. Intra-serial variation for aCL was good; coefficient of variation (CV) for both classes did not exceeded recommended value of20%. Inter-serial CV value was higher (for both classes). It was lower, however, when monoclonal antibodies were used as a standard. The present study also assessed the risk of clinical complications in 336 patients suffering from autoimmune diseases. The stronger risk of both thrombosis and obstretic complications was associated with the presence of lgG aB2GPI antibodies. The risk was som ; ewhat lower for lgG aCL and LA. Our results confirm and justify further attempts to standardize methods of aCL and ab2GPI determination. We also emphasize the need to use in daily practice generally accepted reference calibrators and control materials such as monoclonal antibodies.