Immune activated monocyte exosomes alter microRNAs in brain endothelial cells and initiate an inflammatory response through the TLR4/MyD88 pathway

The host immune response is critical for homeostasis; however, when chronic low level activation of the immune response with or without the driver continues, a cascade of events can trigger immunological dysfunction. Monocytes are key peripheral sensors of the immune response and their activation is instrumental in the development of cognitive impairment. Here, we show that monocytes activated by interferon alpha, lipopolysaccharide or a combination of both generate exosomes carrying significantly altered microRNA profiles compared to non-activated monocytes. These exosomes alone can activate human brain microvascular endothelial cells to stimulate adhesion molecules, CCL2, ICAM1, VCAM1 and cytokines, IL1β and IL6. This activation is through the toll like receptor 4 (TLR4)/myeloid differentiation primary response gene 88 (MyD88) pathway that activates nuclear factor-κB and increases monocyte chemotaxis. Inhibition of monocyte exosome release reverses endothelial cell activation and monocyte chemotaxis. Our study suggests that activated monocytes have an impact on brain vascular function through intercellular exosome signaling.