Background Platelet derived chemokines, such as PF-4 and its nonallelic variant PF-4var, are implicated in several aspects of thrombosis and inflammation. Previous study from our group demonstrates a novel interaction between β2-glycoprotein I (β2GPI) and PF-4 or PF-4var.
Objectives To determine PF-4var plasma levels and platelet PF-4var expression (RNA level) in patients with APS and evaluate the correlation with clinical and laboratory parameters of the disease.
Methods From 90 patients, who fulfill the revised diagnostic criteria for APS, blood samples were taken and separate samples of serum, plasma and platelets were isolated. A healthy control (n=55) and a disease control group (SLE, n=30) were included in the study.
Plasma levels of PF-4var were determined using an ELISA, which absolutely discriminates PF-4var from PF-4. Platelet PF-4var and PF4 RNA levels were determined in RNA isolated from platelet preparations using RT-PCR.
Results APS patients showed higher levels of plasma PF-4var compared to healthy individuals or SLE patients (APS: median 137.4 pg/ml; intarquartile range 65.69-219.2 pg/ml versus HD: 60.52 [36.04-97.12] pg/ml, p<0.0001 or SLE: 51.20 [16.37-172.9] pg/ml, p=0.0027). In addition, RT-PCR revealed significantly higher PF-4var expression in platelets derived from APS patients comparing to healthy donors or lupus patients (2-ΔΔCT: APS: 1.461; [0.6743-2.796] versus HD: 0.815 [0.4260-1.132], p=0.0020 or SLE: 0.7505 [0.4790-1.136] p=0.0017). PF-4var levels were significantly elevated in patients with primary APS than those with APS secondary to SLE [p=0.0086]. Regarding the clinical presentation of the disease, patients who experienced thrombotic events versus pregnancy morbidity or arterial versus venous thrombotic events do not show statistically significant difference in PF-4var levels. A positive correlation was revealed between thrombocytopenia and elongation of aPTT with the higher PF-4var levels.
Conclusions Preliminary results suggest that higher PF-4var levels are present in plasma of APS patients and especially in those with PAPS and these are associated with laboratory characteristics indicative for higher risk of thrombotic complications.
Disclosure of Interest None declared