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Immunophenotypic Characteristics of Equine Monocytes and Alevolar Macrophages

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Title: Immunophenotypic Characteristics of Equine Monocytes and Alevolar Macrophages
Author: Odemuyiwa, Solomon Olawole
Department: Department of Pathobiology
Program: Pathobiology
Advisor: Bienzle, Dorothee
Abstract: Hematopoietic cells of the myelomonocytic lineage play a central role in orchestrating both innate and adaptive immunity. They are important in the control of infectious agents and in the pathogenesis of diseases characterized by dysregulated immune response. Like allergic asthma in human patients, recurrent airway obstruction (RAO) of horses is a disease exemplified by chronic airway inflammation in the absence of infectious agents. However, unlike allergic asthma, RAO is marked by preponderance of neutrophils rather than eosinophils in the airways. Attempts to understand the immunological basis of RAO by studying lymphocytes produced equivocal results. This thesis examined the possible role of alveolar macrophages (AM) recovered from bronchoalveolar lavage fluid (BALF) in RAO. Since macrophages are predominantly derived from circulating monocytes, the thesis investigated first the phenotypic characteristics of circulating monocytes, second those of macrophages in vitro derived from monocytes, and finally attributes of AM derived in vivo. Flow cytometric analysis following antibody staining of monocytes from 61 horses showed that the clustering pattern of human leukocytes may not always be extrapolated to horses when using this technique since clusters of granulocytes often spill over into the monocyte population. The study showed that DH24A, a monoclonal antibody directed against CD90, which recognizes T cells in other species, will specifically recognize granulocytes in horses and was therefore used to separate neutrophils from monocytes during analysis. In addition, investigation of circulating monocytes showed that expression of the hemoglobin-haptoglobin receptor CD163 on circulating monocytes is significantly increased in horses with systemic inflammation when compared with healthy horses. Evaluating cytokine and chemokine production by macrophages, it was demonstrated that CD163+ macrophages preferentially expressed IL10 while CD163- macrophages showed predominant expression of CCL17. It was, therefore, concluded that CD163+ IL10-producing macrophages of horses are homologues of the alternatively activated anti-inflammatory macrophage subset of humans. Finally, probing of alveolar macrophages for CD163 and CD206 expression showed a significant reduction in the proportion of CD163+ macrophages in horses with RAO. These findings suggest that RAO is associated with a reduction in anti-inflammatory macrophages, an observation that may in part explain the chronic airway inflammation associated with this disease.
Date: 2012-03

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