Phagocytic activity of leukaemic blasts

Ultrastructural Study of Leukemic Cell Phagocytosis Using the Myeloperoxidase Reaction

The phagocytosis (in the absence of serum factors) of zymosan particles by peripheral leukocytes isolated from ten patients with acute leukemia (AMbL, AMoL, AMML, AUL, ALL and CML-BC) was studied at the electron microscope. An evident phagocytic activity was observed only in the cells in which cytochemical and ultrastructural features suggested that the blast elements belonged to the monocytic series. However, no phagocytosis by unclassifiable leukemic blasts was observed, even though they had some submicroscopic characteristics of the monocytic series. These findings suggest that phagocytic capacity develops during the course of cell differentiation, becoming striking only when the blast cell acquires the ultrastructural features of the pro-monocytic stage. Using the myeloperoxidase reaction, this study also demonstrates a morphological alteration in the degranulation process after the ingestion of zymosan particles in both the blasts and the mature PMN cells of leukemic patients. This defect could be related to the susceptibility to severe infections usually found in subjects with hematological malignancies.

Translocation t(10;17)(p13;q12) in two cases of acute nonlymphocytic leukemia with phagocytic activity of blasts. A new cytogenetic entity?

We report two cases of translocation t(10;17)(p13;q12) found in a series of 278 cytogenetically studied acute nonlymphocytic leukemia cases. Blast cells, in both cases, were undifferentiated and had phagocytic properties. These patients might represent cases of a new cytogenetic entity.

Acute nonlymphocytic leukemia (M7 subtype) with erythrocytic internalization

A case of acute nonlymphocytic leukemia of megakaryocytic lineage or M7 with a conspicuous phenomenon of erythrocytic internalization present in nearly 3% of the leukemic megakaryocytic precursors (LMP) is reported. The phagocytosis was detected at light microscopy and ultrastructural levels. The erythrocyte might have reached the interior of the LMP through cytoplasmic vacuoles that are connected with the extracellular space and that can be considered rudimentary equivalents of the demarcation membrane system (DMS). Erythrocytic internalization is not a specific feature of the mononuclear phagocytic system and can be misleading in the classification of undifferentiated blast cells.

Erythrophagocytosis by acute lymphoblastic leukaemic cells

Phagocytosis of erthyrocytes and platelets by bone marrow blast cells has been noted in 4 patients in the late relapse of acute lymphoblastic leukaemia (ALL). The underlying mechanism is unclear but prolonged course of the disease seems to be a major factor in the emergence of cells with phagocytic properties.