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Published on: April 8, 2016
Lymphocyte subpopulations in pyogranulomas of caseous lymphadenitis
J Walker1, H Jackson, M R Brandon
1Centre for Animal Biotechnology, School of Veterinary Science, University of Melbourne, Parkville, Victoria, Australia.
Insights
Ovine caseous lymphadenitis (CLA) lesions feature organized immune cells within the capsule, including macrophages, B cells, and a high proportion of CD8+ and gamma delta T cells. This suggests ongoing lymphocyte recruitment and a role in chronic CLA disease progression.
Area of Science:
- Veterinary Immunology
- Bacterial Pathogenesis
- Immunohistology
Background:
- Caseous lymphadenitis (CLA) in sheep is caused by Corynebacterium pseudotuberculosis, forming pyogranulomas.
- These lesions are characterized by encapsulated structures containing necrotic tissue and immune cells.
- The cellular composition and organization within CLA lesions are not fully understood.
Purpose of the Study:
- To investigate the cellular architecture and immune cell populations within the pyogranulomas of ovine caseous lymphadenitis.
- To characterize the distribution and types of lymphocytes and macrophages within the lesion capsule.
- To determine the potential role of intracapsular immune cells in the chronic disease process.
Main Methods:
- Immunohistochemistry was used to identify and localize various immune cell markers within CLA lesions.
- Staining for MHC class II, CD4, CD8, gamma delta T cell markers, CD45R (B cells), and factor VIII-related antigen was performed.
- Cellular distribution and relative abundance were analyzed to understand lesion architecture.
Main Results:
- CLA lesions exhibit a distinct layered structure of immune cells within the collagen capsule, adjacent to necrotic tissue.
- An inner layer of MHC class II expressing macrophages is present, followed by a T cell-rich zone.
- The T cell population is characterized by a high proportion of CD8+ and gamma delta T cells relative to CD4+ T cells.
- B cells were identified in an outer layer, and endothelial venules were observed throughout the lymphoid tissue.
Conclusions:
- The organized intracapsular lymphoid tissue, including the presence of endothelial venules, indicates continuous lymphocyte recruitment into chronic CLA lesions.
- The specific T cell profile (high CD8+ and gamma delta T cells) is a distinguishing feature of CLA lesions.
- These findings suggest that intracapsular lymphocytes play a significant role in the ongoing pathogenesis of caseous lymphadenitis in sheep.
Abstract:
Pyogranulomas of ovine caseous lymphadenitis (CLA) are encapsulated lesions resulting from infections with Corynebacterium pseudotuberculosis, a bacterial pathogen able to grow within macrophages. Immunohistology of CLA lesions showed a band of lymphocytes lining the inside of the collagen capsule in intimate contact with necrotic tissue, the intracapsular lymphocytes being organized into three layers. The innermost layer, immediately adjacent to the central necrotic tissue consisted of a narrow band of MHC class II staining macrophages. Cells staining for CD4, CD8 and gamma delta T cell markers were unevenly distributed throughout the lymphoid layer, tending to be more numerous immediately external to the macrophage layer. The intracapsular lymphoid tissue contained a high proportion of CD8+ lymphocytes (CD4:CD8, 1.5:1) and of gamma delta lymphocytes (CD4:CD8:gamma delta, 1:0.7:0.8). External to the T cell-rich zone and adjacent to the surrounding collagen capsule was a dense band of cells, a proportion of which stained atypically for CD45R and were tentatively identified as B cells. CD8+ and gamma delta+ T cells showed similar distributions and their relative abundance, compared with CD4+ T cells, was a distinguishing feature of the CLA lesion. Staining for factor VIII-related antigen clearly showed endothelial venules throughout the intracapsular lymphoid tissue. The presence of endothelial venules and the organized architecture of the lymphoid tissue teleologically argues that lymphocytes are continually recruited into chronic CLA lesions and play an important role in the ongoing disease process.
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