Autoantibodies Directed Against Moesin C_471-577/N_1-297 Are Novel and Specific Biomarkers of Immune Thrombocytopenic Purpura (ITP),

Abstract 3301

Moesin is a member of the protein 4.1 superfamily and shares structure homology with ezrin and radixin. The phosphorylation of moesin increases the aggregation of Fas, activation of capases, and triggers the apoptotic pathways through the Rho-ROCK pathway. The moesin protein is highly expressed in human platelets and phosphorylation of threonine558 is associated with the activation of platelets. Autoantibodies against moesin have not been evaluated in patients with ITP. Thus, we designed and expressed three polypeptides of moesin: N1-297 terminal, α 298–470 helix domain and C471-577 terminal for ELISA assays. Serum samples from patients with ITP (n=148), patients with non-immune thrombocytopenia (n=32), and other patients with hematologic diseases (n=102) as well as gender-matched healthy control subjects (n=50) were evaluated. All ITP patients clinically met an eligibility of ITP minimal standardized criteria from an international working group.¹ The titers of moesin autoanitbodies were significantly elevated in the sera from patients with ITP compared with healthy subjects (Mean of autoantibodies titers = N1-297 0.515/0.155; α298–470 0.252/0.159; C471-577 0.430/0.144, P < 0.01). The levels of moesin autoantibodies against N1-297 and C471-577 in ITP patients were also markedly higher than in patients with non-immune thrombocytopenia (Mean of autoantibodies titers = N-1-297 0.515/0.168; C471-577 0.430/0.103, P < 0.05). However, the titer of autoantibodies against moesin ? 298–470 helix domains was similar in ITP, non-immune thrombocytopenia and in patients with other hematologic diseases. When an autoantibody cut-off value of ±2D in normal control subjects (n=50) was assigned, the serum levels of moesin autoantibodies in ITP patients were found to be elevated in 70% (103/148) positive for N-1-297, 44% (65/148) positive for C471-577 and only 6.1% (9/148) positive for α 298–470. Moreover, patients with non-immune thrombocytopenia (n=9), anaphylactic purpura (n=11) and myelodysplasticsyndrome, MDS (n=12) were all negative for moesin autoantibodies. In other groups of patients with hematologic diseases, multiple myeloma (n=15), pure red cell aplasia (n=2), and autoimmune hemolytic anemia (n=18), only autoimmune hemolytic anemia demonstrated 4.5% (3/18) positive for N-1-297 and all were negative for C471-577. Notably, severe ITP patients with iron deficiency anemia had high serum moesin autoantibodies against N-1-297 and C471-577. We also found 15.6% (6/38) positive moesin autoantibodies against C471-577 in ITP patients with systemic lupus erythematosus (SLE). To validate the ELISA results, we examined the specificity of moesin autoantibodies in ITP by Western blot analysis. Three polypeptides of moesin were run on SDS-PAGE and transferred onto nitrocellulose membrane. The immunoblotting showed autoantibodies against ITP that specifically recognized the moesin C471-577 or N1-297 polypeptide. In conclusion, this is the first study to show the elevation of serum moesin autoantibodies in patients with ITP. We propose that moesin autoantibodies specific for C471-577/N1-297 may be specific serum biomarkers for clinical diagnosis and differentiation of ITP from non-immune thrombocytopenia and other hematologic diseases.