Leukocyte transmigration is a critical step of the inflammatory process. In this project I have examined leukocyte responses to transmigration and endothelial responses to both chemical and mechanical stimuli which are known to be involved in leukocyte transmigration. My work has identified ~2500 differentially expressed genes following endothelial exposure to interleukin-1 beta (IL1β). Interestingly, IL1β induces up-regulation of claudin-1 and pre-b-cell colony enhancing factor and down-regulation of claudin-5 and occludin, which are all involved in maintaining endothelial cell-cell junctions. Analysis of endothelial cell (EC) transcriptional changes following neutrophil transmigration found few differentially expressed genes in comparison to IL1β treated ECs; indicating that the effects of transmigration on ECs are minimal in comparison to the global transcriptional changes induced by IL1β. Atherosclerosis, characterized by monocyte accumulation within the vessel lumen, is found in regions of flow reversal and low time averaged oscillatory shear stress. I have examined the effects of this type of shear stress on endothelial cell gene expression. My data indicates that most genes differentially expressed under these conditions are controlled by low average shear stress rather than flow reversal. These differentially expressed genes are involved in regulating the cell cycle and the immune response. My work shows that cell proliferation is increased following exposure to low steady shear stress or exposure to reversing oscillatory flow in comparison to high steady shear stress. Additionally monocyte adhesion is increased following exposure of ECs to reversing oscillatory flow. My work has also examined the impact of transmigration on monocyte gene expression. I have identified genes which are differentially expressed in monocytes by exposure to EC secretions, monocyte/EC contact, and diapedesis. I have also shown that freshly isolated human monocytes have reduced apoptosis following transmigration. Surprisingly, I also found that monocytes had reduced expression of anti-microbial peptides following transmigration. Overall my work identifies important endothelial and leukocyte transcriptional responses to the process of transmigration which extends from cytokine stimulation through diapedesis.

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