Two distinctive types of lipid histiocytes appearing in the spleen of idiopathic thrombocytopenic purpura. Sea-blue histiocyte and foam cell.

In 11 of 18 spleens surgically removed from patients with idiopathic thrombocytopenic purpura (ITP), the occurrence of sea-blue histiocytes or foam cells were observed. In a few cases, sea-blue histiocytes were found in the lymph nodes or bone marrow. Histochemically the sea-blue histiocytes were proved to contain ceroid or ceroid-like pigments in their cytoplasm. Ultrastructurally numerous intracytoplasmic membrane-bound inclusions, mostly containing tightly laminated materials and intermingling electron-dense amorphous materials or osmiophilic lipid droplets, were present in these cells. In the foam cells, accumulation of excess amounts of phospholipids was histochemically demonstrated in frozen sections, often accompanied by deposition of cholesterol, particularly in advanced cases. Electron microscopically, vacuolar membrane-bound inclusions were found to predominate in their cytoplasm, most of which contained irregularly or loosely laminated materials. Transitional cells between both types of cells were also found light or electron microscopically and ultrastructural transition of sea-blue histiocytes to foam cells was traced. Enhanced phagocytosis of blood cells, including platelets, by sea-blue histiocytes, and gradual transition of the ingested blood cells to the inclusions were confirmed.