title: Serum factors affecting the specificity of anticardiolipin antibodies.
abstract: The effects were investigated of two pretreatments of human serum and plasma test samples on their subsequent reactivity in the anticardiolipin antibody enzyme-linked immunosorbent assay (ACA-ELISA). The first treatment involved heat inactivation of test samples at 56 degrees C for 30 min, a process sometimes used to inactivate samples from suspected human immunodeficiency virus positive individuals. Such treatment significantly increased the IgG ACA unit/mL values of normal sera, but when this effect was examined further, it was found that the increase in binding occurred on both cardiolipin-coated and uncoated wells and was therefore non-specific. Heat inactivation of sera prior to ACA testing should therefore be avoided. The second treatment involved diluting immunoglobulin (Ig)G and IgM ACA-positive sera in normal human serum (NHS) or newborn calf serum (NCS); sera diluted in NHS showed a significant increase in titre, particularly IgM ACA-positive sera. This phenomenon was found to be due to a serum cardiolipin-binding cofactor which enhances antibody recognition. The cofactor is heat stable and is present in normal sera (male and female) and also in IgG ACA-positive sera. The binding of a human IgM monoclonal antibody to cardiolipin was not affected by the cofactor. The cardiolipin/cofactor complex may represent the optimal autoantigen/autoimmunogen and a re-appraisal, therefore, of the clinical relevance of antibodies to cardiolipin and other negatively charged molecules is warranted.
authors.affiliation: Research and Development Laboratories, Medical Innovations Ltd, Labrador, Qld, Australia.
authors.forename: G T
authors.initials: GT
authors.lastname: Layton
authors.forename: S C
authors.initials: SC
authors.lastname: Johnston
authors.forename: N G
authors.initials: NG
authors.lastname: Bertwistle
mesh_terms: D000818:Animals; D000918:Antibody Specificity; D000936:Antigen-Antibody Complex; D002308:Cardiolipins / Q000276:immunology*; D002417:Cattle; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D007070:Immunoglobulin A / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D008297:Male; D011489:Protein Denaturation
chemical_list: D000936:Antigen-Antibody Complex; D002308:Cardiolipins; D007070:Immunoglobulin A; D007075:Immunoglobulin M