Abstract
The cell surface glycoproteins thrombomodulin (TM) and endothelial protein C receptor (EPCR) are major intermediaries in the down-regulation of thrombin and are noted to be shed from endothelial cells (ECs) due to the actions of proinflammatory cytokines, thrombin and other agents. Antiphospholipid antibodies (APLA) have been described as perturbing ECs. The level of protein S (PS) and protein Z (PZ) have been reported to inconsistently relate to the presence of antibodies and clinical outcomes. We previously reported using a coagulation assay system to demonstrate that adverse pregnancy outcomes (APO) are associated with a greater incidence of resistance to the anticoagulant effects of TM. In the current study we measured the plasma levels of soluble TM (sTM), soluble EPCR (sEPCR) as a possible indicator of APLA-EC interaction. We measured levels of free PS, PZ, sTM and sEPCR in patients (pts) with APLA and/or lupus inhibitor (LI), and correlated the findings with a positive or negative history for thrombosis [THRM(+) or (−)]. APO were not assessed at this time. The study group consisted of 26 males and 60 females, ages ranging from 25 to 90 years; mean of 56. GROUP 1: 33 pts with increased (inc) APLA and 24 of them THRM(+), GROUP 2: 16 pts positive for LI and 7 of them THRM(+), GROUP 3: 37 pts positive for both APLA & LI and 21 of them THRM(+). The pts were compared to 49 normal APLA negative donors (CTR). Pts who have moderate to high levels of anticardiolipin and/or anti-β2 glycoprotein I are APLA positive. LI positive pts have prolonged LI sensitive PTT, and are positive for at least two of the confirmatory tests (Hexagonal phase assay, platelet neutralization procedure, and diluted Russel Viper Venom Time Ratio). GROUP 1 has statistically significant (SS) (p<0.05) decreased (dec) sTM, sEPCR, and free PS when compared to CTR (sTM 1.0+/−1.4 vs 5.1+/−3.3ng/ml, sEPCR 43+/−53 vs 145+/−140ng/ml, free PS 63+/−25 vs 76+/−14%). Free PS is SS lower in the THRM(−) vs. THRM(+). PZ levels do not demonstrate SS differences in the subset comparisons. 8% of THRM(+) pts have PZ deficiency (PZ <1.0ug/ml) with none noted in the THRM(−) pts. Free PS is dec in a majority of the THRM(−). This might be related to the much higher % of females in the THRM(−). Therefore issues such as use of OCP, estrogens, current or recent pregnancy might influence PS. The incidents of dec sTM levels (<2.0ng/ml) are surprisingly higher in this group of patients (82%). This is strikingly higher than the CTR (4%). There is no apparent difference in the THRM(+) to THRM(−). The number of patients with dec sEPCR (<5ng/ml) is much lower however; none of the THRM(−) has dec levels. Inc sTM (>8.0ng/ml) nor inc sEPCR (>284ng/ml) is noted in any of the Pts. In GROUP 2, there is SS dec sTM & sEPCR (sTM 1.6+/−1.8ng/ml, sEPCR 42+/−32ng/ml) vs. CTR with no SS difference in the THRM(+) vs. THRM(−). In GROUP 3, sEPCR is SS dec in pts (sEPCR 68+/−100ng/ml) vs. CTR and CTR vs THRM(+) (sEPCR 29+/−25ng/ml). sTM is SS dec in the CTR vs. THRM(+) (sTM 1.3+/11.4ng/ml). Our data shows low levels of sTM and sEPCR in the APLA patients. This might indicate that the levels are consumed by antibody interactions and could indicate that the APLA and associated other antibodies might interfere with their functions. Previous reports indicating a resistance to TM in a coagulation assay method in patients with THRM and APO raises the possibility of an inhibiting substance present in the APLA. Further work in larger patient groups is necessary to clarify these issues.
Plasma protein Z deficiency is common in women with antiphospholipid antibodies