Functional differentiation in acute monoblastic leukemia.

Blasts from the bone marrow of a patient who had acute monoblastic leukemia were studied for functional maturity. Classification of the leukemia was based on cytochemical stains. The blasts were negative when stained with Sudan black B and did not have specific esterase activity. They were rich in alpha-naphthyl butyrate esterase, which was inhibited by fluoride. Functional assays included phagocytosis of Candida albicans, fungicidal activity measured by differential Giemsa staining of the ingested C. albicans, and locomotion using the agarose method to evaluate both random migration and chemotaxis. At a ratio of 20 yeast cells to one monoblast, 80% of the blasts could be stimulated to phagocytize an average of 4.4 organisms. These results compared favorably with the phagocytic potential of normal human monocytes. Candidacidal activity was present, but reduced. At high ratios of yeasts to monoblasts, only ten organisms were killed for every 100 phagocytic blasts. This correlates with the absence of myeloperoxidase activity demonstrated by negative Sudan black B staining. Neither chemotaxis nor random migration could be demonstrated, indicating that monoblasts lacked the apparatus necessary for locomotion. Extrapolation of these findings to normal monocyte maturation suggests that phagocytosis is acquired prior to microbicidal activity, which develops prior to locomotion.