Red Cell Microparticles (RMP) and Other Cell-Derived Microparticles (C-MP) in Hemolytic Anemias

The lifespan of red cells (RBC) are shortened by several mechanisms in hemolytic anemias (HA): Ab-mediated hemolysis in autoimmune hemolytic anemia (AIHA), complement-mediated lysis in paroxysmal nocturnal hemoglobinuria (PNH), microangiopathy in thrombotic thrombocytopenic purpura (TTP) and hemoglobinopathy in sickle cell anemia (SS) and thalassemia (Thal). During hemolysis, RMP are released along with MP from platelets (PMP), endothelia (EMP) and leukocytes (LMP). The role of MP in HA is unknown but may be involved in complications of HA.

We investigated RMP and other MP profiles in the following hemolytic anemias in active phase: 14 patients with AIHA, 10 with TTP, 4 with PNH, 8 with SS or Thalassemia (SS - Thal), along with 60 healthy controls. Whole, citrated blood was centrifuged at 1600xgfor 10 minutes to yield platelet-poor plasma (PPP). Microparticles in the PPP were measured by FITC- or PE-conjugated mAb specific to the aforementioned cell types. Control plasma was prepared in an identical fashion from healthy volunteers. We compared RMP profiles and other MP in HA during active phase and in remission. Associations with clinical features were calculated using the R statistical software.

Means and standard deviations of C-MP in the different types of HA are shown in the TABLE. Mean RMP and PMP were highest in SS-Thal, followed by AIHA. Mean Annexin V binding procoagluant MP were higher in all subgroups of HA and highest in SS-Thal, followed by TTP. EMP in all subgroups was similar or lower than controls.

Regarding clinical associations, high RMP levels were associated with low hemoglobin (p=0. 01), high reticulocytes (p=0. 003), and high LDH (p=0. 01) across all groups. High reticuloctye counts (>3. 0 %) were also associated with significantly elevated PMP (p=0. 04) and total MP counts by Ulex (p=0. 003). HAs in remission had marginally lower RMP levels than controls (p=0. 05). None of the subtypes had significantly higher EMP, LMP, or PMP compared to each other or controls.

The small population yielded large standard deviations in the MP counts and did not allow statistical study among subgroups of patients with HA. However prothrombotic MPs such as Annexin V, PMP tend to be higher in HA. A larger scale future study will clarify this issue. The constellation of elevated LDH, reticulocytes, and decreased hemoglobin were associated with increased RMP. Therefore we suggest that elevated RMP may be viewed as an additional, new diagnostic marker of active hemolysis.

No relevant conflicts of interest to declare.