After MP infection, infected immunocompetent mice (NS + MP group) exhibited significant histological lesions, including cellular infiltration, alveolar-wall thickening, obvious hypersecretion, and even structural collapse (Fig. 2C,E,G), while infected immunocompromised mice (CYP + MP group) only exhibited mild histological lesions (Fig. 2D,F,H). This evidence concerns the gene PPIG and infection.