Transforming growth factor-β (TGF-β) is one of the cytokines that mediate in the inflammatory response mounted by the host after Mycobacterium avium subspecies paratuberculosis (Map) infection. High levels of this cytokine have been associated with the clinical phases of the disease. One of the known actions of TGF-β is the downregulation of macrophage activation.Immunohistochemical techniques have been employed for the "in situ" detection of TGF-β in different types of lesion associated with Map infection. Samples of intestine (ileocaecal valve, ileum and jejunum) with and without lymphoid tissue and mesenteric lymph nodes were obtained from lambs and calves experimentally infected with Map. Samples had been fixed in 10% formalin and embedded in paraffin. The Avidin-Biotin Peroxidase technique was employed, using a polyclonal antibody against human TGF-β (R&D Systems). Lesions present in the samples were classified as: focal, formed by small groups of macrophages, with none or very low number of mycobacteria, located always in the lymphoid tissue and seen in the initial phases of the infection or in animals showing latent or resistant forms; and diffuse forms, composed of an extensive granulomatous infiltrate located in the lymph nodes and intestinal lamina propia, showing moderate to large amounts of bacilli and seen in the advanced stages of Map infection. In all the cases, positive immunolabelling was absent or seen sporadically in macrophages forming focal granulomas, both located in the lymph node or intestinal lymphoid tissue. However, in diffuse granulomatous lesions present in the intestinal mucosa, the majority of macrophages was positive and showed a high intensity of staining. A clear relationship was seen between the presence of high numbers of bacteria in the cytoplasm and the intensity of the staining. These results suggest that high levels of TGF-β could be related to the inability of macrophages to kill Map and the progression of the infection. Low levels of TGF-β, seen in focal lesions, would be related to the initial phases or forms of resistance of the infection.

Sponsorship

This work was founded by grant AGL-2004-07421-C0201 from MEC.