Macrophage-megakaryocyte interaction in bone marrow after high-dose intravenous immunoglobulin therapy

Localization of IgG in bone marrow after high-dose intravenous immunoglobulin therapy (IVIG) was investigated via light and electron microscopy. IgG was incorporated into the cytoplasm of various types of bone marrow cells of all the three lineages, particularly in reticulum cells, fat cells, and megakaryocytes. In addition, both reticulum cells and fat cells showed many elongated cytoplasmic protrusions, which were in contact with the various types of blood cells, especially the megakaryocytes. A filamentous structure was also seen near the point of contact between the cells. Ultrastructural changes of macrophages in bone marrow after IVIG suggest that these cells were activated by IVIG.