Endothelial influences on monocyte maturation
The aims of this project were to determine the phenotype of migrating monocytes and examine the influence transmigration has on their differentiation to macrophages or DC. To determine stages of differentiation and activation of monocytes cultured in the presence of autologous serum without endothelium nine cell surface receptors were used. These cells matured over time with an increase in CD16+ cells and increased major histocompatibility complex II and macrophage mannose receptor (MMR) expression suggesting alternative activation over time compared to cells cultured in foetal calf serum. Monocyte contact with unstimulated endothelium and a gradient of CCL2 also results in cells with an alternatively activated phenotype with a proportion having a tendency to form dendritic cells (DC). Migration of monocytes is markedly enhanced and endothelium is activated by chemokines and cytokines in the context of inflammation. Contact with endothelium activated with interferon gamma (IFNg) prevents monocytes development into alternatively activated macrophages and may bias them towards classical activation. However contact with endothelium activated with an interleukin 10 (IL-10) results in cells with an alternatively activated phenotype with a subpopulation of cells, which remain on the apical surface, showing a tendency to become DC. These results show that IFNg and IL-10 confer different effects on endothelium and monocytes. Manipulation or activation of the endothelium to program the transmigrating cells to become alternatively activated may provide a novel option to alter macrophage function for therapeutic gain.