Polymorphonuclear leukocytes isolated from chicken peritoneal exudates have been found to catalyze cyanide-insensitive stimulation of respiration and the hexose monophosphate shunt upon exposure to heat-inactivated Staphylococcus aureus. However, there was no demonstrable formate oxidation concomitant with phagocytosis in either the presence or absence of exogenous catalase. Moreover, chicken polymorphonuclear leukocytes failed to oxidize scopoletin concomitant with phagocytosis in the presence of horseradish peroxidase. While oxygen uptake was increased 2-to 3fold by the stimulus of phagocytosis, the oxidation of [1-'4Clglucose was increased approximately 20-fold. The cells contain two mechanisms, a glutathione reductase-glutathione peroxidase system and an NADPH-NAD+ transhydrogenase, each of which is present in sufficient capacity to accommodate the enhanced shunt activity. Although chicken polymorphonuclear leukocytes were found to possess a substantial capacity to catalyze the cyanide-insensitive oxidation of either NADH or NADPH, the total or specific activities of such processes were not demonstrably affected by phagocytosis. The myeloperoxidase (MPO)-hydrogen peroxide-halogen system is deemed an important bactericidal mechanism of polymorphonuclear leukocytes (PMN) (1). However, in a few reported cases, individuals have been found to have PMN deficient in MPO although they are healthy and free of bacterial infections (2, 3). Previous investigations by one of the authors has established that the PMN of chickens are naturally devoid of MPO although they are quite capable of lethal activity against a variety of microorganisms (4, 5). As potential bactericidal mechanisms, the chicken PMN contain a family of six low-molecular-weight cationic proteins and two structurally distinct lysozymes (6). Because it is devoid of MPO, we have considered the possibility that chicken PMN provide a naturally occurring counterpart of the MPO-deficient PMN of humans. In order to further explore this possibility, we have evaluated certain of the parameters of oxidative metabolism in chicken PMN. Such a study might pinpoint fundamental similarities or differences in the biochemical characteristics of the PMN of chickens and humans, thereby adding to an increased understanding of the bactericidal mechanisms of both cell types. EXPERIMENTAL Chicken PMN were elicited and harvested from the peritoneal cavity in essentially the same fashion and purity as described previously (4, 5 to the incubation system at a level of 105 cpm per flask; the specific activities were 45, 53.7, and 24.5 mCi/mmol, respectively. H'4COONa was prepared for use by acidification and evacuation (followed by subsequent neutralization) to remove any contaminating 14CO2. Evolved '4CG2 was collected on Fiberglas paper containing 0.2 ml of 20% KOH, and the radioactivity was determined in a toluene-Triton

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