Morphological differences in the interactions between human mononuclear cells and coated or uncoated sheep red blood cells: a freeze-etch study of different types of rosettes.

Enriched preparations of E, EA and EAC rosettes formed by human peripheral blood mononuclear cells were freeze-etched and examined electron-microscopically. In E rosettes only lymphocyte were involved, whereas in EA and EAC rosettes lymphocytes and mononuclear phagocytes participated as rosette-forming cell. In EA and EAC rosettes, cytoplasmic extensions of the rosette forming cell were seen to penetrate the sheep red blood cell, whereas E rosettes showed a broad zone of adherence without penetration. None of the three types of rosettes showed an interspace between the membranes. Unlike E rosettes, EA and EAC rosettes showed polarity in the adherence of sheep red blood cells. These observations made by freeze-etch electron microscopy indicate distinct morphological differences between rosettes formed with coated or uncoated erythrocytes.