Background and objectives: The aim of the present study is to evaluate and compare IgG-binding to 
megakaryocytes in bone marrow of ITP and MDS patients to determine megakaryocytes targeting by 
autoantibodies in vivo as a mechanism of platelet underproduction in these disorders. Subjects and 
methods: The study was carried out on 20 ITP (group I) patients and 20 thrombocytopenic patients 
with myelodysplastic syndrome (group II) who were admitted to minia university hospital. Serial 
histological sections from bone marrow biopsies were stained for IgG. Results: high IgG binding was 
found in ITP and MDS patients (group I & II ) and there was no statistically significant difference 
between both groups ((14/20 (70%) vs. 13/20 (65%),), (P value =0.736). Conclusion: Antibody 
binding to megakaryocytes in a proportion of MDS patients suggests that immune mediated 
mechanism underlies PLT underproduction in those patients