DIFFERENTIATION LINKED EXPRESSION OF P28,33 (IA-LIKE) STRUCTURES ON HUMAN LEUKEMIC-CELLS

A differentiation linked expression of Ia-like (B [bone marrow derived] cell associated) structures was detected by heterologous antisera against p28,33 antigen on human leukemic cells in immunofluorescence test. A double fluorochrome immunofluorescence test was used to distinguish Ia positive [immune response associated] (p28,33+) leukemic cells from B lymphocytes. Leukemic cells with varying intensities of anti-p28,33 staining were separated using the Fluorescence Activated Cell Sorter. The results indicate that p28,33 is very strongly expressed on undifferentiated blast cells from Philadelphia chromosome (Ph1) positive lymphoid blast crisis and non-T [thymus derived], non-B acute lymphoid leukemia. In Ph1 positive myeloid blast crisis and in acute myeloid leukemia the p28,33 antigen was only moderately strongly expressed on myeloblasts and virtually absent on promyelocytes. The p28,33 antigen was also absent on the relatively more mature cells during the chronic phase of chronic myeloid leukemia. Non-leukemic samples such as bone marrow samples from fetus, and from patients with severe megaloblastic anemia or myeloid hyperplasia (due to hypersplenism in Felty syndrome), were also found to contain p28,33 positive (and membrane immunoglobulin negative) immature blast cells. On the basis of these observations the hypothesis is proposed that Ia-like antigens on leukemic cells refect the origin of these leukemias from hemopoietic stem cells which are themselves Ia positive. The corollary of this view is that Ia-like membrane structures may play an important role not only in immunological responses of B cell, but also in the regulation of early hemopoietic cell differentiation.