Inducible nitric oxide synthase immunoreactivity in the granulomatous intestinal lesions of naturally occurring bovine Johne's disease

Inducible nitric oxide synthase (iNOS) is important in the control of a number of intracellular pathogens, including mycobacteria, and is a marker of classic macrophage activation. In human granulomatous diseases such as leprosy, a spectrum of granulomatous lesions is described, ranging from the tuberculoid to lepromatous types. Tuberculoid granulomas are associated with enhanced iNOS production and improved clinical outcomes over the lepromatous types. The aim of this study is to determine whether an association exists between morphology of bovine Johne's disease granulomas and lesion macrophage effector functions. To accomplish this, we retrospectively evaluated 24 cases of bovine Johne's disease. In each case, we recorded the predominant granuloma morphology and evaluated iNOS immunoreactivity and bacterial burden by acid-fast stains and mycobacterial immunolabeling. The results of this study demonstrate that all cases had granulomas with features most similar to the lepromatous type. This morphology correlated with heavy bacterial burdens demonstrated by acid-fast staining and mycobacterial immunoreactivity. None of the cases had high expression of iNOS in mycobacterial-positive granulomas. When iNOS immunoreactivity was identified, it was usually located near the crypts and was distinct from the granulomatous foci.