In the past differentiation of human neutrophils has been defined by morphology, cytochemistry, or surface markers. In our experiments we have sequenced the various events that occur during the functional differentiation of the normal human neutrophil and have also examined some of the functional properties in relationship to surface markers and biochemical events. Granulocytes were obtained from the bone marrow and blood of hematologically normal individuals. Cells were separated into different stages of maturation by their physical properties using counterflow centrifugal elutriation and density gradient separation. Three cell fractions were obtained that were enriched for either immature myeloid cells, band neutrophils, or segmented neutrophils. Since the enriched fractions were not entirely pure, methodologies for functional assays were chosen that allowed cytologic evaluation of the functional capacity of each cell type. The criteria used to classify the stages of differentiation included both morphology by light microscopy and DNA labeling with tritiated thymidine. Various neutrophilic properties were studied: Fc receptors, complement receptors (CR1, CR3), phagocytosis of both live and dead opsonized Staphylococcus aureus, microbial killing of S aureus, NBT dye reduction after cellular stimulation with endotoxin, and chemotaxis. Our results indicate that the functional properties of the neutrophil appear in a distinct order. The sequence for the functional differentiation of the human neutrophil appears to be the following: Fc receptors----immune phagocytosis----complement receptors----oxygen-independent microbial killing----oxygen-dependent microbial killing----chemotaxis.

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