Methodological approach for the detection of IgM anticardiolipin antibodies

The effects of 10% fetal calf serum (10% FCS), 10% adult bovine serum (10% ABS) and 1% bovine serum albumin (1% BSA) buffers on the reactivity of samples with or without IgM anticardiolipin antibodies (ACA IgM) were studied on cardiolipin-coated wells (target wells) and cardiolipin-free wells (control wells) in an ELISA test. With 1% BSA, target well reactivity was very low for samples containing ACA IgM. The 10% FCS induced a moderate but significant binding of polyclonal IgM on target wells particularly in the case of IgM hypergammaglobulinemia. With 10% ABS, whatever the IgM serum level, this non-specific binding did not occur on the solid phase either in the presence or in the absence of cardiolipin. Using 10% ABS, the study of 35 SLE sera showed that non-specific binding of IgM on control-wells occurred only with ACA IgM positive samples. Thus with the use of 10% ABS, we propose that subtraction of control well from target well values must not be performed for the detection of ACA IgM. The significance of cardiolipin-free well IgM reactivity of ACA IgM positive sera is discussed.