Electron microscopy of E-rosette-forming leukemic monocytes in a child with acute monocytic leukemia

A 7-year-old boy with acute monocytic leukemia (AMoL) had leukemic monocytes that formed spontaneous rosettes with sheep red blood cells (E-rosette). The E-rosette formation was observed in 75% of leukemic monocytes at 4 C and in 37% at 37 C. Cytochemical and ultrastructural studies confirmed that the rosette-forming cells were leukemic monocytes. The leukemic monocytes attached to the red blood cells at a portion of their surface and did not show any phagocytic processes at the electron microscopic level. The data from this patient seem to indicate that in a rare case of AMoL, abnormal myeloid lymphoid stem cells can differentiate to monocytes while retaining lymphoid properties.