Histopathological and immunohistochemical findings in the lungs of pigs infected experimentally with Mycoplasma hyopneumoniae.

Pigs were infected intranasally with Mycoplasma hyopneumoniae and killed at intervals ranging from 7 to 35 days post-infection (dpi). Histopathological changes consisted of (1) exudates in airways and alveolar lumina, (2) peribronchial and peribronchiolar lymphoid hyperplasia, and (3) enlargement of alveolar septa. These changes were particularly marked from 7 to 28dpi, coinciding with significant increases in the expression, detected immunohistochemically, of cytokines (IL-1alpha, IL-1beta, IL-8, TNF-alpha and INF-gamma) and lymphoid markers (CD4+, CD8+, muramidase, IgG+, IgA+). Both the lesions and immunohistochemical signals declined in intensity beyond 35 days.