Cofactor dependent and cofactor independent anticardiolipin antibodies.

Two distinct types of anticardiolipin antibodies are described, one of which requires the presence of a serum factor (cofactor) to bind cardiolipin in ELISA and liposome affinity systems. The second type does not require this cofactor. The requirement of a cofactor for the binding of some but not all anticardiolipin antibodies provides an explanation for the confounding variability of the results of assays for these antibodies. It also explains why blocking agents such as BSA and gelatin do not produce consistent results in this assay.