CD11b- macrophages (“resident” macrophages) constituted the predominant macrophage population in the lung parenchyma of unchallenged mice and at early time points post-infection, while the number of CD11b+ macrophages (“recruited” macrophages) increased, starting around day 5 and peaking around day 8 post-infection (Fig 4B). This evidence concerns the gene ITGAM and infection.