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Leukocytes play a key role in the host defense. When the human body is invaded by foreign pathogens, the leukocytes migration into inflammatory sites is mediated by several adhesion molecules, which include the integrin family molecules, such as LFA-1, Mac-1, p150/95, and immunoglobin family, such as ICAM-1 and VCAM-1. We investigated the adhesion mechanisms of leukocytes including lymphocytes and eosinophils. Lymphocytes are important in adaptive immune responses, which provide an increased level of protection from subsequent re-infection of the same pathogen. Eosinophils (Eos) are effector cells in asthma and other allergic diseases. They release inflammatory mediators and toxic proteins that cause tissue damage in allergic response.
Firstly, we tested the adhesion function of lymphocytes form patients with Down syndrome. Our data showed that lymphocyte adhesion to ICAM-1 was impaired in children with Down syndrome, even though the expression level of cell surface LFA-1 in Down syndrome patients was comparable to that of normal controls.
Secondly, we investigated the adhesion function of eosinophils. Previous studies had shown that the eosinophils used CD11b/CD18 (Mac-1)(β2 integrins ) or very late antigen-4 (VLA-4) to bind to ICAM-1 and VCAM-1, respectively, on the endothelial cells. However, little is known about the interaction between eosinophils and epithelium. In order to clarify the adhesion molecules mediating eosinophil-epithelial adhesion, a panel of monoclonal antibodies (mAbs) against eosinophils was prepared. We used these mAbs to study the adhesion between eosinophils and epithelial cells. The data showed that all these anti-Eos mAbs stain on eosinophils. Some also stained on other cell type including neutrophils, JY (B cell) and Jurkat (T cell). We explored the cell surface staining by using resting and IL-5 treated eosinophils from allergic patients and eosinophils isolated from a patient with Churg-Strauss syndrome. The data showed that for some of the molecules recognized by mAbs, resting eosinophils expressed lower levels of these molecules when compared with eosinophils treated with IL-5 or eosinophils from the patient with Churg-Strauss syndrome. We measured adhesion ability of eosinophils to respiratory epithelial cells with a cell-to-cell adhesion assay. Blocking of the anti-eosinophil mAbs on eosinophils with E3, E10, E15, E16, E18, E19, E20, E21, E22 reduced the number of eosinophils adhered to epithelial cells (A549) by 20~50%. We also measured the respiratory burst of eosinophils primed by different cytokines and anti-Eos mAbs. The result showed that some of the molecules recognized by these anti-eosinophil mAbs might have roles in eosinophil respiratory burst. Our data suggested that these mAbs will be useful tools to investigate the adhesion and migration mechanisms of eosinophils and epithelial cells.
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