By measuring the levels of the enzyme MPO, we found a significant accumulation of neutrophils in lung parenchyma of WT mice at day 5 after infection (Figure 2B), whereas in PI3Kγ deficient mice, levels of MPO were already augmented at day 3 after infection and were higher than those found in WT mice throughout the course of infection (Figure 2B). Here, MPO is linked to infection.