Origin of crystalloid inclusions in macrophages II: evidence for derivation from eosinophil granulocyte breakdown.

Abstract Peritoneal macrophages were studied by light and electron microscopy in normal adult mice 24 h after 3 daily injections of preparations of leucocytes and platelets. Crystalloid inclusions, similar to those seen in bone marrow macrophages of normal adult mice and in man, were occasionally observed in peritoneal macrophages after administration buffy-coat white cells but not after platelets. They were much more frequently seen following the ingestion of eosinophil-rich granulocytes and were almost always associated with secondary lysosomes. Energy-dispersive analysis of X-ray provided further evidence that both crystalloid inclusions and lysosomes originated from the injected granulocytes. These observations suggest that crystalloid inclusions in marrow macrophages are derived from granulocyte breakdown and that in this respect eosinophil granulocytes are of prime importance.