Morphological and immunological similarity of the monocytes from pure and mixed monocytic leukaemias.

Morphological and immunological marker data on a patient with 'pure' monocytic leukaemia are presented and compared with those of 6 cases of clearly mixed myelomonocytic leukaemia with a variable monocytic component. In all patients studied, the leukaemic monocytes expressed a receptor for the Fc of IgG, and IgG sensitization markedly enhanced phagocytosis of ox erythrocytes. A variable, but lower, percentage of the leukaemic monocytes had a receptor for mouse C3, but the cells uniformly lacked surface immunoglobulin and receptors for the Fc of IgM and for unsensitised mouse erythrocytes. Cytochemical and ultrastructural study also showed no clear difference between the monocytes of the 'pure' and mixed monocytic leukaemias. This report therefore lends no support to the concept of distinct types of monocytic leukaemia.