Identification of four subpopulations of IgG anticardiolipin antibodies in patients with primary antiphospholipid syndrome on the basis of their requirement for beta 2-glycoprotein-I and their unmasking by heat.
Heat-treatment of normal human serum (NHS) results in positive seroconversion of IgG anticardiolipin antibodies (aCL) that do not depend on beta 2-glycoprotein-I (beta 2GP-I) for their detection in vitro as do some IgG aCL from patients with primary antiphospholipid syndrome (PAPS). Other IgC aCL from PAPS depend on beta 2GP-I for phospholipid binding. Here, we studied heat-unmasked aCL from 22 PAPS sera and from eight normal individuals. IgG aCL were detected in standard (using new born calf serum [NBCS] that contains beta 2GP-I as blocking agent and to dilute samples) and in a modified ELISA (using beta 2GP-I-free-bovine serum albumin instead of NBCS). Overt and heat-unmasked IgC aCL were purified from CL micelles alone or mixed with purified beta 2GP-I. NHS had no overt IgG aCL. In contrast, aCL titers increased almost ten-fold after heat-inactivation of NHS, a result which was equally detectable in both assay conditions. As expected, PAPS patients had one population of overt beta 2GP-I-dependent IgG aCL. After heat-treatment of all PAPS sera, we detected IgG aCL in both standard and modified aCL ELISA with an approximately three-fold increase in IgG aCL titers when tested in the standard assay. Two PAPS patients also had a second population of beta 2GP-I-independent overt IgG aCL. Purified IgG from these PAPS sera retained both reactivities.(ABSTRACT TRUNCATED AT 250 WORDS)
Department of Immunology and Rheumatology, Instituto Nacional de la Nutrición Salvador Zubirán, Mexico D.F., Mexico.
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Cabral
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Alarcon-Segovia
D017153:Antibodies, Anticardiolipin / Q000032:analysis* / Q000145:classification*; D016736:Antiphospholipid Syndrome / Q000276:immunology*; D001053:Apolipoproteins / Q000502:physiology; D006023:Glycoproteins / Q000502:physiology*; D006358:Hot Temperature; D006801:Humans; D007074:Immunoglobulin G / Q000032:analysis*; D053482:beta 2-Glycoprotein I
D017153:Antibodies, Anticardiolipin; D001053:Apolipoproteins; D006023:Glycoproteins; D007074:Immunoglobulin G; D053482:beta 2-Glycoprotein I