Essential role of endothelial cells in mediating neuronal responses to systemic immune stimuli. Mice were exposed to total-body irradiation and were injected via a tail vein with bone marrow cells freshly collected from green fluorescent protein (GFP) mice. Chimeric mice were perfused transcardially 2 months later and their brains were processed for immunohistochemistry. CD31-positive cells were stained with a rhodamine red-X-conjugated secondary antibody (red blood vessels), whereas GFP was used to label perivascular microglia (elongated green cells). In this study, Gosselin and Rivest have used this approach to study the respective contribution of both cell types in the brain response to circulating interleukin 1 and lipopolysaccharide. They reached the conclusion that nuclear factor kappa B signaling in endothelial cells is essential to trigger neuronal and endocrine functions to both immune ligands. For more information on this topic, please refer to article by Gosselin and Rivest on pages 480-497.