Regulation and role of different macrophage-and granulocyte-inducing proteins in normal and leukemic myeloid cells.

It has previously been shown that there are different molecular forms of macrophage-and granulocyte-inducing (MGI) proteins; one form, MGI-l, induced the formation of colonies with differentiated cells from normal myeloblasts and another form, MGI-2, induced normal differentiation in MGI+D+ leukemic myeloblasts that no longer require MGI-l to form colonies. The present results indicate that MGI-2 can also induce differentiation (without inducing colony formation) in the normal cells, and that MGI-l induced MIG-2 in the normal but not in the leukemic cells. It is suggested from these results that MGI-2 is the differentiation-inducing protein for normal and leukemic cells whereas MGI-l is the growth-inducing protein that induces colony formation by the normal cells, and that induction of differentiation in the normal cell colonies is due to induction of MGI-2 by MGI-l.