Inhibitor(s) ofnatural anti-cardiolipin autoantibodies

SUMMARYIgGfractions were purified on Sepharose anti-human IgG columnfrom eight sera of healthydonors,having no anti-cardiolipin (aCL) activity as measured by anti-cardiolipin ELISA assay (aCL-ELISA). Allthe IgGfractions, afterelutionwith49 M MgCI2, reactedwithCL.The antigen-binding characteristics ofthe IgG fractions purified fromnormalhuman serum (NHS) were similartothoseof IgG fractions purified from sera offour patients with the anti-phospholipid syndrome(APLS).Competition assay confirmedthe specificity ofthe binding ofthe purified IgG fractions to CL.The same results havebeen achieved with IgG fractions purified on Sepharose Protein-A column. The binding to CL was completely inhibited by eitherwholeNHSand sera fromvariousanimal species, or by #2-glycoprotein I(12-GPI). Ourresultssupportthenotionoftheexistenceofbothnaturalanti-CLantibodies and serum inhibitor(s) in sera of healthy individuals. It is conceivable that in part the pathogenesis ofAPLSentails defects in the natural inhibitors ofaCLantibodies.