[Chyliform effusions in rheumatoid arthritis. Cytochemical and ultrastructural studies of the foam cells].

The authors studied the cell composition and the cytochemistry and ultrastructure of the frothy cells in two periarticular chyliform effusions in rheumatoid arthritis. Compared with the polymorphonuclear cells, the mononuclear cells were very numerous with many frothy cells. Cholesterol crystals, identified by X-ray diffraction, were detected in fluids by polarised light, but only cytochemically and with the transmission electron microscope in the spumous cells. The latter contained not only neutral fat, but also hydrophobic lipids and phospholipids, but no cholesterol esters. A theory has been advanced that once phagocytosis has been accomplished, cholesterol crystal metabolism is not rapid and is too insufficient for cholesterol or its esters to accumulate in the cytoplasm. The polymorphonuclear leukocytes play only a small role in the phagocytosis of crystals and this probably plays a role in the absence of acute inflammation in structures which contain chyliform effusions.