Hematoxylin–eosin staining
After mice were sacrificed, their entire heads and spleens were soaked
in 10% neutral formalin fixative for 24 h, because the nasal cavity of
BALB/c mice is small. Afterwards, the heads were soaked in 0.5 M
ethylene diamine tetraacetic acid for decalcification for 4 weeks. After
the mouse skull was softened, the tissues were conventionally
dehydrated, embedded in paraffin, and sectioned in the coronal position
(about 3 μm thick slices). The histopathological changes of the nasal
mucosa were visualized with hematoxylin–eosin staining. The same steps
were applied to the spleens.