Relationship of acid phosphatase activity to ultrastructural features in mice inoculated with Mycobacterium paratuberculosis

A preliminary study of possible genetic influences on the susceptibility of sheep to Johne's disease

OBJECTIVE

To investigate possible genetic influences on susceptibility or resistance of sheep to Johne's disease.

DESIGN

A field and laboratory study of two fine-wool Merino flocks with a high prevalence of disease due to Mycobacterium avium subsp paratuberculosis infection.

PROCEDURE

Adult sheep were phenotypically classified as having severe, mild or no disease on the basis of clinical, pathological and cultural tests for paratuberculosis, and as positive or negative in tests for humoral immunity (agar gel immunodiffusion test) or cell mediated immunity (skin test for delayed type hypersensitivity). Correlations with phenotype were sought for polymorphisms at loci within selected immune function genes (NRAMP, MHC complex, IFN-gamma, lysozyme, leukaemia inhibiting factor).

RESULTS

Possible associations of particular NRAMP and MHC alleles with susceptibility or resistance to Johne's disease were detected.

CONCLUSION

If the results of this preliminary study are confirmed in further work, then the use of rams with "resistant" genotypes may assist in the control of Johne's disease in infected flocks.

Characterization of macrophages and occurrence of T cells in intestinal lesions of subclinical paratuberculosis in goats

The granulomatous lesions of subclinical paratuberculosis of goats were examined with emphasis on phenotypic characteristics of macrophages and the presence of different subpopulations of T cells. The macrophages in the granulomatous lesions were morphologically homogeneous in histological sections but showed varying expression of the macrophage marker CD68 (a glycoprotein found mainly in late endosomal and lysosomal membranes) and varying acid phosphatase activity. The lesional macrophages showed decreased expression of complement receptor 3 and major histocompatibility complex proteins, which are markers associated with phagocytosis and antigen-presentation, respectively. The granulomas showed low proliferation activity as measured by the proliferation-associated protein Ki-67, indicating that most cells were recruited to the lesions. Few apoptotic cells were demonstrated by the TUNEL technique, suggesting a low cell turnover in the lesions. CD4(+) T cells constituted the main T-cell population among the CD68(+) macrophages in the granulomatous lesions, and few CD8(+) T cells and gamma delta T cells were observed within the lesions, suggesting the limited ability of these cells to influence the granulomatous lesions in caprine subclinical paratuberculosis. Both WC1(+) and WC1(-) gamma delta T cells were present in the small intestinal wall, but the latter were the more numerous. No difference in the numbers of these cells was observed between the subclinically infected animals and control animals.

T cell-dependent inducible nitric oxide synthase production and ultrastructural morphology in BALB/c mice infected with Mycobacterium avium subspecies paratuberculosis

Euthymic BALB/c and athymic nude BALB/c mice aged 3-8 days were infected intraperitoneally with Mycobacterium avium subspecies paratuberculosis (ATCC strain 19698). After euthanasia at 5 months post-inoculation, hepatic granulomas were evaluated by morphometric analysis of digital images captured from light microscopy sections, by electron microscopy and by immunohistochemical methods. Euthymic mice differed from athymic mice in that (1) their hepatic granulomas were smaller, contained fewer bacteria, and produced more inducible nitric oxide synthase, and (2) their hepatic macrophages contained fewer bacteria, a higher percentage of degraded bacteria, and increased numbers of primary lysosomes. The study showed that macrophage activation was markedly less in the T cell-deficient athymic mice than in the euthymic mice.

A role for lymphotoxin beta receptor in host defense against Mycobacterium bovis BCG infection

To investigate the role of membrane lymphotoxin (LT)alpha1 / beta2 and its LTbeta receptor (LTbetaR) in the protective immune response to Mycobacterium bovis bacillus Calmette-Guérin (BCG) infection, we have used a soluble fusion molecule (LTbetaR-IgG1). LTbetaR-Ig treatment interferes with granuloma formation mainly in the spleen by inhibiting macrophage activation and nitric oxide synthase activity. In addition, a large accumulation of eosinophils was observed in the spleen of LTbetaR-Ig-treated infected mice. Decreased blood levels of IFN-gamma and increased IL-4 were also observed, suggesting that the LTbetaR pathway is important in BCG infection to favor a Th1 type of immune response. The treatment of transgenic mice expressing high blood levels of a soluble TNFR1-IgG3 fusion protein with LTbetaR-Ig resulted in a still higher sensitivity to BCG infection, and extensive necrosis in the spleen. In conclusion, these results suggest that the LTbetaR and the TNFR pathways are not redundant in the course of BCG infection and protective granuloma formation: the LTbetaR pathway appears to be important in spleen granuloma formation, whereas the TNFR pathway has a predominant role in other tissues.