CYBB and systemic inflammatory response syndrome: Although there is no difference in PSGL-1 expression on neutrophils in the peripheral blood of WT and gp91phox−/y mice under resting conditions, there is a rapid decrease in PSGL-1 expression on circulating neutrophils in the gp91phox−/y mice by 2 h post SIRS, with a concomitant increase in PSGL-1 expression on neutrophils in the BAL fluid, suggesting that the “higher” expressing neutrophils have migrated into the alveolar space (Figures 5A,B).