Decrease in the Density of IgG-Fc Receptor III (CD16) on ‘Toxic’ Neutrophils

Osamu KabutomorI, Central Laboratory for Clinical Investigation, Osaka University Hospital, 1-1-50 Fukushima, Fukushima-ku Osaka 553 (Japan) Changes in human peripheral blood neutrophils frequently occur during serious bacterial infections and certain other inflammatory states [1]. Best known is the ‘shift to the left’ defined by the presence of band forms of neutrophils, metamyelocytes, and sometimes myelocytes [2]. ‘Toxic’ neutrophils, which have azurophilic cytoplasmic granules in blood smears stained by the Wright or May-Grünwald-Giemsa stain [3], are another sign of bacterial infection in the blood. The migration, chemotaxis, phagocytosis, and bactericidal activity (measured by counting of the number of colonies formed by surviving bacteria) of toxic neutrophils are less than those of normal neutrophils [4], but myelo-peroxidase activity, a major bactericidal factor in phagocytes, is higher in toxic neutrophils [5, 6]. Therefore, the decrease in bactericidal activity observed in such neutrophils may arise from the decrease in phagocytosis. Much has been reported about the relationship between cell function and cell surface antigens, and measurement of the density of cell surface antigens is useful for the diagnosis of some pathological conditions [7, 8]. The cell surface antigen(s) related to phagocytosis is unknown, but it seems that the CD16 antigen, which is an IgG-Fc receptor [9], is important for immunophagocytosis by neutrophils [10]. In this study, we examined the relationship between the density of CD16 antigen on neutrophils and the number of toxic neutrophils in patients with bacterial infections. In a sample, the mean fluorescence intensity of CD16+ neutrophils stained with an anti-CDló monoclonal antibody conjugated with fluorescein isothiocyanate reflects the density of CD16 antigen on neutrophils. This intensity was exu 500S. o .¤ > c 3⁄4 φ is ¢ø Φ