Figure 7. Pathogenic Findings Following Homologous Challenge.

Light photomicrographs of representative histologic lung sections (Table 1, experiment 2) taken from an untreated control mouse (A), a VRP-N–vaccinated mouse (B) and (D), a VRP-HA–vaccinated mouse (C), a VRP-S–vaccinated mouse (E), and a VRP-S– and VRP-N–treated mouse (F). No histopathology was evident in (A). A marked mixed inflammatory infiltrate composed mainly of mononuclear leukocytes (lymphocytes and plasma cells) and widely scattered eosinophils are evident in the perivascular and peribronchiolar interstitium (asterisk) in (B). Similar inflammatory cells are also present in bronchiolar (br) airways and alveolar airspaces along with enlarged and vacuolated alveolar macrophages (arrows). The box in (B) denotes the site of the light photomicrograph (D) that was taken at a higher magnification to better illustrate the lymphoplasmacytic inflammatory cell infiltrate with lesser numbers of eosinophils (arrows). Similar, but slightly less severe, perivascular inflammatory infiltrates (asterisk) are also present in (F), but without accompanying alveolitis. Minimal lymphoplasmacytic cell accumulations around the pulmonary arteriole (a) are evident in (C) and (E). All tissues were stained with hematoxylin and eosin. Bars denote the scale of the magnification. a, pulmonary arteriole; ap, alveolar parenchyma; br, bronchiolar lumen; e, surface epithelium of the bronchiole.