Pulmonary histopathology. (a) Representative light photomicrographs of lung tissue sections, stained with hematoxylin and eosin, showing a peribronchiolar and perivascular mixed inflammatory cell infiltration in HDM mice (arrows). aw: airways; a: airspace; v: blood vessel; scale bar: 500 μm. (b) Accumulation of major basic protein positive eosinophils (arrow) in the perivascular and peribronchiolar region of young and old HDM mice. tb: terminal bronchioli; a: alveoli; v: blood vessel; scale bar: 50 μm.