Increased Prevalence of Anti-CD36 and Elevated Endothelial Microparticles in Patients with Recurrent Thrombosis.

BACKGROUND: CD36 is a widely distributed transmembrane glycoprotein, called GpIV on platelets, involved in various physiologic processes. It has been implicated in thrombogenic pathologies such as diabetes, atherosclerosis and anti-phospholipid syndrome (APS). It is also an adhesion molecule capable of interacting with collagens and is considered a platelet collagen receptor. We investigated autoantibodies (Ab) against CD36 in TTP [Schultz et al, BrJH 103:849, 1998]. The present study was undertaken to explore relationships of anti-platelet Ab (aPlt-Ab), antiphospholipid Ab (APLA), and circulating cell-derived microparticles (MP) in patients with thrombosis.

METHODS: Forty-five patients with documented thrombosis (TB) referred for hypercoagulable workups were recruited consecutively. Of them, 18 suffered from recurrent thrombosis (rTB) while 27 had a single event (sTB) within the past 5 years. We measured APLA, lupus anticoagulant (LA), antiplatelet antibody (aPlt-Ab) and MP. The APLA were IgG and IgM against cardiolipin (CL) and β₂-glycoprotein-I (β₂GP1) measured by ELISA. The aPlt-Abs were IgG and IgM reacting to GpIIb/IIIa (CD41b), GpIb/IX (CD42b), and GpIV (CD36), assayed by the PAICA method of Macchi et al [Thromb Haemost 76:1020, 1996]. The following types of MP were measured by flow cytometry: endothelial MP defined by CD31+/CD42− (EMP₃₁) or by CD62E+ (EMP₆₂); platelet MP defined by CD31+/CD42+ (PMP); leukocyte MP defined by CD45+ (LMP); and red blood cell MP by glycophorin+ (RMP). Lupus anticoagulant (LA) was measured in the hospital clinical laboratory and was considered positive if 2 of 3 different test methods were positive. Platelet activation was measured by CD62p expression in flow cytometry.

RESULTS:

1. Although both groups had increased prevalence of APLA and LA, there were no significant differences between the sTB and rTB groups. About 70% of patients in both groups were positive for at least one APLA.

2. Of the aPlt-Ab, only aGpIV (aCD36) statistically discriminated between the groups, being more frequent in rTB for both IgG (p<0.02) and IgM (p<0.02).

3. Among the MPs assayed, PMP were elevated in all patients in both groups. EMP₆₂ discriminated best between rTB and sTB (p=0.003). LMP and RMP were also significantly higher in rTB than sTB, p<0.025. When we compared patients CD36+ vs CD36− we found that EMP₆₂ was more frequently elevated in CD36+ patients (7/12, 58%) than in CD36− patients (2/32, 6%), p=0.001.

4. Platelet activation marker CD62p was more often increased in rTB than sTB, p=0.022.

CONCLUSION: GpIV (CD36) antibodies are the most prominent risk factor for rTB to emerge from this study. This confirms a previous report [Pelegri et al, Clin Exp Rheum 21:221, 2003]. EMP, LMP, RMP and platelet activation (CD62p) are also increased in the recurrent TB group vs single TB. EMP₆₂ were associated with aCD36. Since CD36 is found also on endothelial cells, this suggests that aCD36 could be responsible for the high EMP₆₂ in the rTB group. The present study demonstrates an association between high EMP₆₂ and aCD36. We suggest that persisting autoantibodies against GpIV activate EC to predispose to recurrent thrombosis.