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). This evidence concerns the gene SELPLG and systemic inflammatory response syndrome.