Induction of CD13 expression on fresh myeloid leukaemia: correlation of CD13 expression with aminopeptidase-N activity.

CD13 has proved to be a useful cell surface marker for depicting haematopoietic cells of the myeloid and monocytic lineages. Sequence data has shown CD13 to bear strong homology to Aminopeptidase-N. Expression of this antigen on myeloid leukaemic cells is, however, variable. We have looked at the effects of a phorbol ester PMA and a haematopoietic growth factor GM-CSF on the expression of CD13 displayed by a selected group of myeloid leukaemias at presentation and by normal peripheral blood granulocytes. We have found that PMA but not GM-CSF was able to stimulate CD13 expression on fresh myeloid leukaemic cells but granulocytes were stimulated by either PMA or GM-CSF. In addition, we have correlated CD13 expression with Aminopeptidase-N enzyme activity on fresh myeloid leukaemic cells. These results suggest that CD13 is functionally active on leukaemic cells and normal granulocytes.