A chimeric antibody with the human gamma 1 constant region as a putative standard for assays to detect IgG beta(2)-glycoprotein I-dependent anticardiolipin and anti-beta(2)-glycoprotein I antibodies

Objective. Thromboembolic manifestations or thrombocytopenia in association with anticardiolipin antibodies (aCL) or lupus anticoagulant are known as the antiphospholipid syndrome (APS), Efforts have been made to elucidate pr ecise clinical features and adequate therapeutic options for treating patie nts with APS, However, the lack of a proper international standard for meas urement of aCL makes it difficult to compare data derived from different la boratories. We attempted to design a chimeric antibody with human gamma con stant regions and variable regions of WBCAL-1, a monoclonal antibody establ ished from an APS-prone mouse which has a specificity similar to that of aC L in sera from humans with APS, Methods. Variable-region genes of WBCAL-1, which were cloned using reverse transcription-polymerase chain reaction, were inserted into plasmids contai ning human gamma 1 and kappa constant-region genes. The construct was trans fected to a mouse myeloma cell line. Stable transfectants that secreted a c himeric antibody, HCAL, into the culture supernatant were obtained. The rea ctivity of HCAL to cardiolipin and to beta(2)-glycoprotein I (beta(2)GPI) w as studied using a solid-phase enzyme immunoassay, The binding of HCAL was compared with the binding of standards for IgG aCL and anti-beta(2)GPI anti body assays done in 18 independent laboratories. Results, In the presence of beta(2)GPI, HCAL bound to the wells of cardioli pin-coated microtiter plates in a dose-dependent manner and reacted with be ta(2)GPI on oxygenated polystyrene plates. The aCL activity of HCAL can be converted into GPL units (IgG phospholipid units), which is widely used to quantify IgG aCL activity, using the following formula: 1 GPL unit 32.9 x ( concentration of HCAL [in mu g/ml])(0.503). The reactivity of HCAL to cardi olipin or beta(2)GPI was similar to the reactivity of standards for IgG aCL or anti-beta(2)GPI antibody assays done in collaborative laboratories. Conclusion. Because the reactivity of HCAL is similar to that of aCL in ser a from humans with APS, HCAL will be useful as a standard for human IgG aCL and anti-beta(2)GPI antibody assays.