MEMBRANOUS LAMELLAR CYTOPLASMIC INCLUSIONS IN HISTIOCYTES AND MESOTHELIAL CELLS OF SEROUS FLUIDS - THEIR RELATIONSHIP TO PHAGOCYTOSIS OF RED-BLOOD-CELLS

OBJECTIVE: To define the composition of cytoplasmic inclusions forming stacks and concentric whorls in histiocytes and mesothelial cells of serous fluids, imparting to them a resemblance to Gaucher cells, and t o draw conclusions on the mechanism of their formation. STUDY DESIGN:T hree serous fluids tone pleural and two pericardial) containing a fair number of the cells referred to were progressively subjected to the f ollowing studies: (1) cytochemistry for mucopolysaccharides, proteins, phospholipids and hemoglobin; (2) immunocytochemistry for immunoglobu lins IgA, IgG, IgM and lysozyme; (3) transmission electron microscopy (TEM), and (4) scanning electron microscopy-based energy dispersive X- ray microanalysis (SEM-EDAX). RESULTS: All three specimens were blood stained and contained large numbers of histiocytes and mesothelial cel ls, arranged singly and in groups, with abundant cytoplasmic inclusion s. The inclusions stained strongly positive for phospholipids, weakly positive for hemoglobin and negative for all other substances examined by cytochemistry and immunocytochemistry. By TEM the: inclusions had a concentric lamellar membranous structure, reminiscent of myelinosome s or lamellar bodies of lipid-forming or - storing cells. There Tons a lso phagocytosis by histiocytes and mesothelial cells of red blood cel ls, which were mostly in a degenerated state. SEM-EDAX of inclusion-be aring cells showed a modest peak for phosphorus and a variable but sma ll peak for iron, which corroborated the cytochemical and TEM findings . CONCLUSION: Since there tons no metabolic or other systemic disease in the patients to account for these cells, we posit that phospholipid s derived from cell membranes of phagocytized cells, especially red bl ood cells, provide the building blocks for the formation of such inclu sions as they enter the metabolic pathway of phagocytic cells (mesothe lial cells and histiocytes) and appear in their lysosomal structures. It is advantageous for cytologists to be familiar with the significanc e of such changes and not to mis take them for evidence of metabolic o r other systemic disease.