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Two antigens (Mo1 and Mo2) present on human peripheral blood monocytes have been defined by lytic IgM monoclonal antibodies. Both antigens are present on greater than 70% of adherent mononuclear cells (predominantly monocytes). Mo1 is expressed by monocytes, granulocytes, and Null cells, but is absent from T and B lymphocytes. Mo2, on the other hand, appears specific for peripheral blood monocytes. Neither antigen is present on Ia-positive B cell lines or on tumor cells from patients with B cell lymphoproliferative malignancies, further excluding the possibility that Mo1 and Mo2 are Ia antigens. Mo1 and Mo2 are, however, present on a significant number of blast cells from patients with monocytic leukemia (both myelomonocytic and pure monocytic variants), but relatively infrequently expressed by cells from patients with acute granulocytic leukemia. These results indicate that Mo1 and Mo2 are unique antigens that may represent distinct stages of late monocyte-granulocyte differentiation.
Todd et al. (Wed,) studied this question.