The leukaemic hairy cell in culture lacks the monocyte marker, angiotensin converting enzyme induction.

Hairy cells of hairy cell leukaemia are unique circulating mononuclear cells of questionable origin which possess features of both B-lymphocytes and monocytes. Angiotensin converting enzyme, which is consistently induced in monocytes in culture, was not induced in hairy cells in culture. This result is consistent with a lymphocytic rather than a normal monocytic cell lineage for the hairy cell. The origin of other monocytic phenotypic characteristics remains to be explained.