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.

In vitro responses to purified protein derivate of caprine T lymphocytes following vaccination with live strains of Mycobacterium avium subsp paratuberculosis

Live attenuated vaccines provide protection against intestinal lesions in goats infected with Mycobacterium avium subsp. paratuberculosis. To examine the role of different T lymphocyte subsets in the development of this protective immunity, CD4(+), CD8(+) and gamma delta T cell receptor (TCR)(+) cells from peripheral blood of goat kids vaccinated with live attenuated strains of M. a. paratuberculosis were studied. After in vitro stimulation with purified protein derivate, the expression of gamma-interferon (IFN-gamma) and the activation marker interleukin-2 receptor (IL-2R) was analysed by flow cytometry. A depletion experiment was performed, where the phenotypes and IL-2R expression was studied after stimulation of cultures depleted of a T lymphocyte subpopulation. Close to all of the IFN-gamma producing cells were of the CD4(+) subset, while only a small number were CD8(+) cells. The gamma delta TCR(+) cells were highly activated, but did not produce IFN-gamma after in vitro stimulation. Depletion of CD4(+) cells lead to a decrease in the percentage of total gamma delta TCR(+) cells and gamma delta TCR(+)IL2-R(+) cells. Removing the gamma delta TCR(+) cells increased the relative numbers of CD4(+), but not the CD4(+)IL-2R(+) cells. Insight into the in vitro recall responses of T cell subsets from animals vaccinated with live paratuberculosis vaccines is essential in the development of more efficient vaccines.

Localisation of CD25+ cells and MHCII+ cells in lymph nodes draining Mycobacterium avium subsp. paratuberculosis vaccination granuloma and the presence of a systemic immune response

Vaccination of goat kids against paratuberculosis protects against lesions and clinical disease. The systemic cellular response was studied in goat kids 3-9 weeks after vaccination. Peripheral blood cells showed increased interferon-gamma production and expression of interleukin-2 receptor (CD25) after stimulation with Mycobacterium avium subsp. paratuberculosis antigens. The lymph node draining the vaccination granuloma was studied three weeks after vaccination in a parallel group of goat kids. In deep cortex, MHCII+ cells were observed surrounded by CD4+ T-cells, while follicular hypertrophy and hyperplasia were prominent in the subcapsular region and along connective tissue trabecula. Comparison of the local and systemic immune responses revealed an inverse relationship between CD25+ T-cells in the lymph node deep cortex and cells in peripheral blood that up-regulate CD25 upon in vitro stimulation, suggesting that activated and regulatory T-cells in the local lymph node influence the level of circulating antigen-specific T-cells following vaccination against paratuberculosis in goats.

Lesions in subclinical paratuberculosis of goats are associated with persistent gut-associated lymphoid tissue

The organized gut-associated lymphoid tissue (the Peyer's patches [PPs] of domestic ruminants) is an important site of lesions caused by Mycobacterium avium subsp. paratuberculosis. To investigate the association between PP morphology and the lesions of paratuberculosis in goats, two experiments were performed. Five healthy kids aged 4-5 weeks were examined and the morphology of organized lymphoid tissue in the small intestine was described. Morphological similarities were observed between the ileocaecal-valve PP (ICVPP) and the jejunal PPs (JPPs), with pear-shaped follicles, large submucosal interfollicular T-cell areas, and many intraepithelial leucocytes in the follicle-associated epithelium. The ileal PP (IPP) consisted of elongated follicles, small T-cell areas and few intraepithelial leucocytes. The association between these three locations of PPs and lesions of paratuberculosis was then studied in seven goats inoculated with M. a. paratuberculosis at 5-8 weeks of age and killed 2 years later, while in the subclinical phase of infection. Gross lesions were recorded in five animals and microscopic lesions were observed in the intestine and mesenteric lymph nodes of six animals. The lesions in the small intestine were mainly located in the PPs of the mid-jejunum (JPPs) and ICVPP. Lesions were not present in the intestinal segments that had contained IPP, which had undergone involution during the first 12-18 months of life. These observations indicate that the persistent organized lymphoid tissue in the JPPs and ICVPP, but not the involuted IPP, sustains the development of granulomatous inflammation due to paratuberculosis during the subclinical phase of infection.

Subclinical paratuberculosis in goats following experimental infection. An immunological and microbiological study

An experimental oral infection of goats with a caprine isolate of Mycobacterium a. subsp. paratuberculosis was used to investigate immunological and bacteriological events during the subclinical phase of infection. Seven goats at 5-8 weeks of age were given a bacterial suspension in milk-replacement three times weekly for 9 weeks. Six animals were kept as controls. Cellular recall responses against M. a. paratuberculosis were analysed by means of a lymphocyte proliferation test, an IFN-gamma assay and an IL-2 receptor assay. All inoculated animals had detectable CMI responses from 9 weeks post-inoculation and through the 2 years of study, although the responses were highest during the first year. Antibodies against M. a. paratuberculosis could be detected from weeks 15-20 in four of the seven animals, and one additional animal became antibody positive at week 35, while two inoculated animals did not produce significant antibody titres during the experiment. At about 1-year post-inoculation, two animals became faecal shedders, while two others started to excrete bacteria into faeces about 2 years post-inoculation. The appearance of M. a. paratuberculosis in faeces was not associated with a decline in cellular responses as far as could be assessed using the current methods for measuring CMI. Pathological lesions due to M. a. paratuberculosis infection and presence of bacteria were recorded in the intestine and/or mesenteric lymph nodes of five animals while lymph node changes suggestive of paratuberculosis were observed in one animal. Only the two animals with no signs of an active infection at necropsy showed a considerable decline in the cellular parameters during the last year of the study, particularly in the IFN-gamma assay. The two animals with the highest levels of M. a. paratuberculosis responsive CD8+ lymphocytes in the circulation about 1-year post-inoculation had no detectable lesions in the distal ileum and colon at necropsy, while high numbers of gammadelta T-cells responsive to M. a. paratuberculosis in the circulation were associated with disseminated lesions in the distal ileum and colon.

Disseminated Mycobacterium celatum (type 3) infection in a domestic ferret (Mustela putorius furo)

A 4-year-old male ferret (Mustela putoriusfuro) had a 6-month history of weight loss and gradual development of depression and coughing. Necropsy findings included pale gray tissue around the distal trachea, multiple nodules in the lungs, a single nodule in the stomach wall, gray foci in the liver, and enlarged lymph nodes. Histologic examination revealed multifocal to coalescing granulomatous inflammation in the trachea, lungs, stomach, liver, and lymph nodes, with acid-fast bacteria in epithelioid cells and macrophages. The acid-fast bacteria were identified as Mycobacterium celatum (type 3) using DNA sequence analysis of the 16S ribosomal DNA gene. M. celatum is a recently described mycobacterium isolated mainly from immunocompromised humans. This is the first report of M. celatum infection in an animal.