Alveolar macrophages (AMs) are essential for maintaining lung homeostasis. However, their roles in respiratory infections have been controversial because the methods of depleting them have often suffered from poor cell selectivity. To resolve this problem, we here used VeDTR technology to generate a transgenic mouse line in which AMs can be specifically depleted using diphtheria toxin. When various respiratory infections were examined using this system, we found that AMs prevented the proliferation of