Abstract
Neutrophils, triggered by heat-aggregated human IgG (Agg.IgG), were found to lyse chicken red blood cells (CRBC) as determined by a 51Cr release method. The lysis was inhibited by azide, catalase, chloride- free medium and amino acids, suggesting the requirement for myeloperoxidase (MPO), hydrogen peroxide (H2O2), chloride ions (Cl-), and hypochlorous acid (HOC1), respectively. These results indicate that neutrophils lyse CRBC through an HOCl-(ie, MPO-H2O2-Cl-) dependent process. Although HOCl can react with neutrophil-derived nitrogenous (N- ) compounds to yield chloramines, the main and well-characterized chloramines did not play a direct role in the lysis of CRBC in our model system. Thus, it appears that lysis is due either to HOCl or to an unknown compound derived from and with characteristics similar to HOCl. When CRBC were replaced with HRBC targets, no lysis could be observed. Treatment of HRBC with carmustine, to inhibit the glutathione cycle, did not affect the cell resistance to lysis by neutrophils. Conversely, the inhibition of HRBC catalase activity with aminotriazole (AT) made the cells susceptible to neutrophil-mediated HOCl-dependent lysis: this suggests that HRBC escape lysis by neutrophils through an AT-inhibitable, ie catalase-dependent, process. Through an identical catalase-dependent process, HRBC were capable of efficiently preventing the H2O2 and HOCl recovery from Agg.IgG-triggered neutrophils, tested under experimental conditions similar to those used for cytolytic assays. Together, these data suggest that HRBC targets, endowed with high catalase activity, escape neutrophil-mediated lysis by consuming (by catalase) neutrophil-derived H2O2, so that HOCl cannot be produced in amounts sufficient to promote lysis. Parallel experiments, performed with AT-treated CRBC, showed that these cells, endowed with a relatively low catalase content, only partially limit neutrophil cytolytic efficiency by a process qualitatively similar to that observed with HRBC targets. The results provide evidence that target cells can restrain neutrophil cytolytic efficiency by interfering with the MPO-H2O2-Cl system through their catalase activity.
