Correlations of Red Cell-Derived Micropareticles (RMP) with Other MP Species in Hematological and Thrombotic Disorders

Background: We have recently observed that increased levels of circulating RMP are associated with several hematological disorders and thrombophilic states, and that levels were significantly higher when thrombosis was present. However, other species of MP, such as from platelets (PMP), endothelia (EMP), leukocytes (LMP) and annixin V-binding (AnV) have also been shown to be associated with thrombophilic states. The purpose of this study was to determine if correlations exist between RMP and other MP.

Methods: This is a retrospective analysis of 702 laboratory samples over an 8 year period, limited to elevated values: >2SD above normal controls (>2,000/uL).. About 87% were individuals, the remaining 13% were tested 2-3 times and all tests >3 per patient were excluded. The disorders were hemolytic anemia (HA, n=38), hypercoagulable state (HCS, n=64), immune thrombocytopenia (ITP, n=86), thrombocytopenia of all causes (TP, n=69), myeloprolifereative disorder (MPD, n=29), thrombotic thrombocytopenic purpura (TTP, n=29), antiphospholipid syndrome (APS, n=34), pulmonary embolism (PE, n=21), and all-cause thrombosis (TBS, n=251). Some were classified in more than one way. MP species assayed were RMP by glycophorinA, PMP by CD41 (PMP41), PMP by CD42 (PMP42), EMP by CD31+/42- (EMP31), EMP by CD62E (EMP62E), LMP by CD45, annexin V binding (AnV), and counts by lectin, FITC-Ulex, which efficiently detects total MP including very small.

Results: In HCS, the RMP >2,000/uL correlated well with PMP41 (R=0.407, p <0.001) and with PMP42 (R=0.285, p =0.02). In ITP, the RMP correlated solely with PMP42,31 (R=0.331, p =0.003). In HA, the RMP correlated with LMP (R=0.408, p =0.009) and with PMP42 (R=0.340, p =0.03). In all-cause TBS, RMP correlated with PMP41 (R=0.164, p =0.0120 and with LMP (R=0.231, p <0.001). In MPD, the RMP correlated solely with ulex (R=0.343, p <0.01). There was no significant correlation between RMP >2,000/uL and any of the MP markers in APS, TP, or TTP. The MP species markers, EMP31, EMP62E, and AnV, failed to show correlation with RMP in any of the disorders analyzed. In addition, we tested for correlations between elevated RMP and other MP for the entire data set (all disorders combined) and found that only LMP was significant (p <0.05). However, when the data was sorted by increasing LMP, it was found that the highest quintile showed improved correlation with RMP (p <0.01) while the lowest quintile of LMP values yielded no correlation at al (p > 0.05).

Discussion: These correlation analyses shows that RMP correlated most frequently with PMP, as seen in HA, ITP, HCS, and TBS, followed by LMP, as seen in HA and TBS. These observations suggest that platelet or/and leukocyte activation may be involved in RMP generation. Of added interest is the finding that the overall data correlated well with LMP only at the higher LMP levels, not at all in the lower quintile of LMP. This suggests that RMP elevations are associated with immunolgic, inflammatory processes. In summary, correlation analysis reveals likely interaction between red cells and platelets or leukocytes during immunologic, inflammatory or in thrombophilic states, resulting in elevated RMP.