ANTICARDIOLIPIN ANTIBODIES DO NOT SEEM TO BE ASSOCIATED WITH APC RESISTANCE IN-VIVO OR IN-VITRO

Anticardiolipin antibodies (aCL) or lupus anticoagulants (LA) have bee n found to exert an inhibitory action upon the activation and function of protein C, a natural coagulation inhibitor. Recently an in vitro p henomenon called resistance to activated protein C (APC resistance) ha s been described as the most frequent cause of hereditary thrombophili a. In order to see whether a positive association of APC resistance wi th aCL exists we examined plasma of 162 consecutive outpatients referr ed for thrombophilia screening. Further, the IgG fraction was isolated from plasma of two aCL-positive and LA-negative patients and of two a CL-negative healthy subjects by means of protein A affinity chromatogr aphy. Each of these isolates was mixed with normal plasma, and the APC resistance was assayed; 25/162 (15.4%) patients had confirmed abnorma l APC resistance. Only 1/25 (4.0%) APC resistance-positive patients an d 11/137 (8.0%) APC resistance-negative patients had positive IgG- and /or IgM-aCL (p = 0.5, nonsignificant). In the in vitro test system the APC resistance ratio remained unaffected after addition of normal IgG or aCL-IgG fraction in the tested normal plasma and did not deviate f rom the range of buffer controls. These data do not suggest any associ ation of aCL with abnormal APC resistance. aCL-IgG fractions from aCL- positive and LA-negative plasmas do not interfere with the APC resista nce test system in vitro in low concentration.