DIFFERENCES IN PROTEIN-S AND C4B-BINDING PROTEIN-LEVELS IN DIFFERENT GROUPS OF PATIENTS WITH ANTIPHOSPHOLIPID ANTIBODIES

Total protein S (tPS), free protein S (fPS) and C4b-binding protein (C 4b-BP) were measured by immunological assays in 73 patients with antip hospholipid (aPL) antibodies, in order to determine whether the previo usly reported abnormalities in PS levels in this group of patients cou ld be related to the presence of lupus anticoagulant (LA) or anticardi olipin (aCL) antibodies. As compared with the normal controls (n = 44) , the authors found a significant decrease of tPS, fPS and C4b-BP in 4 5 LA(+)aCL(+) patients (P < 0.001), a decrease of tPS (P < 0.001), fPS and C4b-BP (P < 0.02) in eight LA(-)aCL(+) patients and a decrease of only fPS (P < 0.05) in 20 LA(+)aCL(-) patients. There was no differen ce in the levels of tPS, fPS and C4b-BP between LA(+)aCL(+) and LA(-)a CL(+) patients. In contrast, the LA(+)aCL(+) patients had lower values of tPS, fPS and C4b-BP than LA(+)aCL(-) patients (P < 0.05). In some patients, protein S activity (PSact) was also measured and a high corr elation was observed between fPS antigen and PSact (r = 0.93, P < 0.00 1). The data show that the presence of aCL antibodies is associated wi th a probably acquired deficiency of PS and C4b-BP. On the other hand, in LA patients without aCL antibodies, the fPS deficiency is unrelate d to an increase in C4b-BP levels and may be due to abnormal binding o f PS to C4b-BP.