Flow cytometric analysis of intracellular CD68 molecule expression in normal and malignant haemopoiesis.

CD68 molecules are heavily glycosylated lysosomal membrane constituents of unknown function with strong expression in monocytes and macrophages. Using flow cytometry, we quantified expression levels of CD68 molecules in normal and malignant haemopoietic cells. CD68 molecules are intensely expressed in the cytoplasm and weakly on the surface of mature CD14+ monocytes. CD68 expression seems to start very early during granulomonopoietic differentiation. Virtually all myeloperoxidase (MPO)+ bone marrow cells coexpress CD68 and similar proportions of CD34+ progenitor cells weakly express CD68 or MPO molecules. During further differentiation, CD68 expression is strongly up-regulated in early MPO+ precursor cells which lack lactoferrin (LF) and CD14 molecules. Compared to these, more mature MPO+LF+ bone marrow and peripheral blood granulocytes express considerable lower levels of CD68. In-line with this broad expression, all investigated acute myeloid leukaemia (AML) cases, classified as FAB M1-M5, were CD68 positive, and compared to normal CD34+ bone marrow cells. CD34+ AML blast cells expressed increased levels. CD68 expression is, however, not restricted to cells of myeloid origin, because a subset (40 +/- 15%, n = 6) of CD19+ peripheral blood B-lymphocytes and 50% of B-ALL are also weakly positive. In contrast, normal CD3+ lymphocytes lack (< 3%, n = 6) CD68 and only low proportions (6 +/- 3%, n = 6) of CD56+ NK cells are CD68+. Also, all investigated T-ALL cases (n = 6) lacked CD68.