CD16 DOWN REGULATION IN GRANULOCYTES INCUBATED WITH CLOZAPINE.
JC Delgado, OP Clavijo and EJ Yunis. Department of Pathology, Brigham & Women’s Hospital and Department of Cancer Immunology & AIDS, Dana-Farber Cancer Institute, Harvard Medical School, Boston, MA.
Clozapine-induced agranulocytosis is observed in 1% of patients taking the drug. In vitro studies have demonstrated that granulocyte survival is decreased when they are incubated in the presence of clozapine. In this study we have analyzed whether neutrophil apoptosis is stimulated in the presence of clozapine. In vitro culture of purified granulocytes from healthy human volunteers were performed in the presence or absence of clozapine. We analyzed neutrophil apoptosis using annexin V-FITC binding and the expression of two cellular receptors, CD16 and CD66. After 2 hours of incubation with clozapine, we observed a statistically significantly decreased in the expression of CD16 in comparison to control cells. Although, annexin V-FITC binding was increased in granulocytes incubated in the presence of clozapine, the difference was not statistically significant. It has been reported that down regulation of CD16 in neutrophils correlates with the appearance of apoptosis.
Our results suggest that CD16 down regulation in granulocytes precedes morphological apoptotic changes such as annexin binding. More importantly, decreased neutrophil survival in the presence of clozapine may be due to increased apoptosis susceptibility. Previously, we have reported that susceptibility and resistance to clozapine-induced agranulocytosis are associated to specific HLA haplotypes in Jewish and non-Jewish patients. Therefore, neutrophil susceptibility or resistance in patients taking clozapine may also correlate with these specific haplotypes.