Fc gamma RII and Fc gamma RIII on normal leukaemic granulocytes: a flow cytometry and northern analysis.

Morphologically mature granulocytes from patients with chronic myeloid leukaemia (CML) exhibit a defect in internalization of heat-aggregated IgG. In order to investigate this defect at the molecular level and, in turn, the discordant maturation of these granulocytes, we compared the expression of Fc gamma RII and Fc gamma RIII, the two receptors for IgG on the surface of granulocytes, in normal and CML samples. Our flow cytometric data show that the number of granulocytes expressing Fc gamma RIII is lowered in CML patients to near half that in normal individuals, with a simultaneous decrease in the steady-state levels of the mRNA for Fc gamma RIII. Mean fluorescence intensity (MFI), an indicator of the number of receptors per cell, varies widely for Fc gamma RIII in normal individuals whereas it is more localized and lowered in granulocytes from CML patients. The number of granulocytes positive for Fc gamma RII is also significantly lowered in CML samples compared to the normals, which exhibit a wide variation in the number of cells positive for the receptor, even though their nRNA levels do not vary much. The CML granulocytes, in general, exhibit lowered levels of the steady-state mRNA for Fc gamma RII. The MFI for the surface expression of Fc gamma RII is only marginally different between the two cell types. Our data indicate that the morphologically homogeneous population of CML granulocytes actually consists of at least two types of cells, one which expresses the Fc receptors and one which does not.