High dose intravenous immunoglobulin therapy (IVIG) has been performed for increase of platelet to patients with immune-thrombocytopenia (ITP). We observed by standard and immunoelectron microscopy the phenomenon of the direct cell to cell contact between red blood cells (RBCs) and endothelial cells (ECs) in bone marrow (BM) of patients with ITP (ITP-patients) after IVIG and then compared to that of the mice injected human immunoglobulin (IgG). RBCs were observed to adhere directly to the ECs

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... blood vessels in BM of both the ITP-patients and of the mice injected with high dose human IgG. However, in the mice injected with saline, no RBC was seen adhering to the EC as well as that of ITP-patients before IVIG. We concluded that the direct adherence between RBC and EC in the BM after high dosed human IgG injection is not due to an immunological mechanism at all.