Compared with WT PCP mice, the neutrophil percentages were higher in lung [(16.3 ± 2.7 vs. 9.2 ± 0.8)%, P = 0.038] and blood [(28.8 ± 1.8 vs. 18.8 ± 1.3)%, P = 0.004] of IL-9−/− PCP mice (Figure 7B). This evidence concerns the gene IL9 and pneumocystosis.