Intestinal Strictures, Fibrous Adhesions and High Local Interleukin-10 Levels in Goats Infected Naturally with Mycobacterium avium subsp. paratuberculosis

This study describes pathological findings and their association with the production of interferon (IFN)-γ and interleukin (IL)-10 in goats infected naturally with Mycobacterium avium subsp. paratuberculosis (MAP). Twenty-seven goats were subjected to pathological examination. More than half of the animals had severe, diffuse, transmural granulomatous enteritis, often with abundant acid-fast bacilli (AFB), which was most evident in the proximal jejunum. Jejunal strictures and fibrous, peritoneal adhesions were findings that are not often reported in animals with paratuberculosis. Immunohistochemical labelling of IL-10 was seen within diffuse, granulomatous lesions and this may have prevented optimal local IFN-γ production and exacerbated the disease. However, since IFN-γ production was detected in cells from blood, jejunum and jejunal lymph nodes of goats with severe lesions by enzyme-linked immunosorbent assay, intracellular labelling and in-situ hybridization, the up-regulation of IL-10 might have been a consequence rather than a cause of the severe disease. The IL-10 labelling was co-localized with major histocompatibility complex (MHC) class II+ cells, but rarely with CD4+ cells. Comparable numbers of CD4+ and CD8+ T cells were recruited to both severe, diffuse lesions and small to moderate granulomatous lesions, while few T cells expressing the γδ form of the T-cell receptor were associated with both types of lesions.