Background Platelet microparticles (PMP) contain pro-coagulant as well as pro-inflammatory substances like platelet activating factor (PAF) and P-selectin. Rheumatoid arthritis (RA) is associated with increased concentrations of both PAF and P-selectin, but the link with PMP has never been investigated.
Objectives To test the hypothesis that patients with RA have elevated levels of PMPs and that these levels are associated with disease activity.
Methods This was a descriptive study in patients with RA, using neither anticoagulants nor corticosteroids. The patients were divided in two groups, according to disease activity. Criteria for active RA were: ESR at least 28 mmh and/or CRP at least 28 mg/dl plus more than 8 painful and more than 5 swollen joints. Criteria for RA in remission were: ESR <28 mmh and/or CRP <28 mg/dl plus no painful and no swollen joints. PMPs were determined with flowcytometry (CD61/annexin-V). The values were compared with those from healthy volunteers, using nonparametric tests (Mann-Whitney).
Results Ten patients with active RA and ten patients with RA in remission were included. There were 5 men and 15 women. The mean age was 61 years, the mean disease duration was 6 years and 75% was rheumatoid factor positive (comparable in both groups). The mean number of PMPs in RA patients was 3,173 × 106/L versus 451 × 106/L in healthy volunteers (p = 0.005). See Table 1 for further results:
Conclusion This study confirms the hypothesis that patients with RA have higher numbers of PMPs; moreover, the presence of PMPs is associated with disease activity. This observation is most probably the missing link between the studies on the PMP content in general and the raised PAF- and P-selectin levels in sera from patients with RA. Moreover, one may speculate on the possible meaning of these elevated PMPs for the well-known high mortality due to cardiovascular disease in patients with RA. More research may clarify this.
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