Effects of Intravenous Immunoglobulins (IVIG) on Cell-Derived Microparticles in Patients with ITP.

INTRODUCTION: ITP is an autoimmune disease in which antiplatelet antibodies induce immune-mediated platelet destruction. Cell-derived microparticles (C-MP) are microvesicles released from blood cells as well as endothelial cells (EMP) upon activation or apoptosis of parent cells. MP released from platelets (PMP), leukocytes (LMP), red cells (RMP) and endothelial cells (EMP) are believed to participate in hemostasis, thrombosis and inflammation. We previously reported C-MP profiles in ITP and that platelet counts correlated directly with PMP, and inversely with RMP [V. Fontana et al, ASH 2006, Abst #1087]. This suggests that RMP reflect severity of platelet destruction in ITP. IVIG is widely employed in the treatment of ITP and is believed to ameliorate platelet destruction by down-regulating Fc receptors of macrophages. In this study, we investigated how IVIG infusion affects C-MP levels in ITP patients.

METHODS: Nineteen patients with ITP (7M/12 F, mean age 57.5yr) who received IVIG (20–30 gm/day × 2–5 days) for treatment of ITP were studied. Platelet counts and C-MP were measured before and 24hr post-infusion of IVIG, and platelet counts were monitored for 2–3wks thereafter. Patients were classified as responders (R) or non-responders (NR) to IVIG. Criteria for R was a rise in platelet counts to ≥70,000 and ≥50% increase over pre-treatment values; NR had ≤70,000 and ≤50% incremental increase within 3 weeks of IVIG. Flow cytometry was employed to assay C-MP using fluorescent markers of CD45 (LMP), CD41 (PMP), CD31+/CD41− (LMP), and glycophorin (RMP).

RESULTS: Table 1 summarizes mean values of platelet counts and C-MP in the R and NR groups. The R group had n = 10 patients (7F/3M, mean age 56.4 yr; mean platelets 35,000μL pre, 118,000μL post, p = 0.001), and the NR group had n = 9 patients (4M/5F, mean age 58.8 yr, mean platelets 44,000μL pre, 51,000μL post, p>0.05, n.s.). Mean levels of PMP increased significantly in the R group (p = 0.02) but no change was seen in the NR group. RMP decreased significantly in both groups but the decrease was more significantly in the R group (p=0.002) than the NR group (p=0.01). No significant change in EMP or LMP was seen pre- vs. post-IVIG.

CONCLUSION/DISCUSSION. The present study demonstrates that IVIG modulates C-MP levels in ITP. IVIG decreased RMP significantly in both groups but more so in R than NR groups. It increased PMP in R but not in NR, consistent with our previous report that PMP levels correlated with platelet counts. However there is no effect of IVIG on LMP and EMP. These findings are consistent with the concept that IVIG down-regulates immune-mediated platelet destruction and has little effect on activation of leukocyte or endothelium. Since RMP appear to reflect severity of ITP, the observed decrease of RMP in both groups post-IVIG may reflect amelioration of immune-mediated platelet destruction by IVIG therapy. The mechanism by which RMP are produced in ITP, and how IVIG reduces RMP, remains to be elucidated.