Ultrastructure of the hepatic sinusoids in the tropical splenomegaly syndrome

In Ugandan cases of TSS electron microscopy shows that the hepatic sinusoids are filled by Küpffer cells and lymphocytes. The Kupffer cells are both hyperplastic and hypertrophied, much of the latter being due to extensive proliferation of their surface membranes similar to that of antigen trapping dendritic macrophages from germinal centres. The membrane extensions are apparently functioning as a trapping zone which accumulates an electron-dense deposit on the cell surface. There is no evidence that this deposit is taken up into the cell. A group of cells described here as M cells, though basically similar to Kupffer cells, lack many of the Kupffer cell characteristics and in particular the extensive plasma membrane development. Such cells show considerable evidence of uptake of material via large coated vesicles and have fewer mitochondria and less endoplasmic reticulum than the Kupffer cells. They probably represent a different functional development from the Kupffer cells or possibly from a common stem cell. Many of the lymphocytes show, by their ribosome content, expanded perinuclear space, and increased numbers of endoplasmic reticulum elements and mitochondria, that they are not small lymphocytes but are of the activated lymphocyte series.The general appearance is consistent with a complex immunological reaction occurring in the liver sinusoids.