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Septic shock is the most common cause of death in intensive care units and no effective treatment is available at present. Lipopolysaccharide (LPS) is the primary mediator of Gram-negative sepsis by inducing the production of macrophage-derived cytokines. Previously, we showed that apolipoprotein E (apoE), an established modulator of lipid metabolism, can bind LPS, thereby redirecting LPS from macrophages to hepatocytes in vivo. We now report that intravenously administered LPS strongly increases the serum levels of apoE. In addition, apoE can prevent the LPS-induced production of cytokines and subsequent death in rodents. Finally, apoE-deficient mice show a significantly higher sensitivity toward LPS than control wild-type mice. These findings indicate that apoE may have a physiological role in the protection against sepsis, and recombinant apoE may be used therapeutically to protect against LPS-induced endotoxemia.Sepsis is a syndrome referring to an exaggerated systemic response to infections, which can ultimately lead to death from septic shock. In fact, in the United States the incidence of sepsis has increased during the last decennia (1) and sepsis has become the most common cause of death in intensive care units, with 150,000 deaths annually (2, 3). Many cases of sepsis are caused by Gram-negative bacteria (1). Lipopolysaccharide (LPS), 1 a component of the outer membrane of these bacteria, is the primary cause of Gram-negative sepsis and gives rise to the same clinical features as are observed in patients with sepsis (3-6). Within the blood, the lipid A-moiety of LPS binds to the LPS-binding protein (7,8), and the resulting complex displays a high affinity for CD14-toll like receptor 4 (Tlr4) complex on mononuclear phagocytes (9, 10). Activation of these cells induces the release of inflammatory mediators such as tumor necrosis factor alpha (TNF␣) and interleukins (IL-1␣, IL-1␤, and IL-6). These cytokines are responsible for the metabolic and physiologic changes that ultimately lead to pathological conditions (11-13). The importance of these cytokines in LPS-induced death arises from observations that administration of TNF␣ or IL-1 to animals provokes a similar reaction as detected after injection of LPS (14 -17). In addition, antibodies against TNF␣ protect monkeys (18 -20), rabbits (21), and mice (17) against LPS-induced death. Also, blockade of IL-1 production prevents LPS-induced death of mice (22). Current therapeutic strategies are, therefore, directed against LPS (bactericidal/permeability-increasing protein (BPI), antibodies against LPS (23, 24)), cytokines (soluble TNF receptor, anti-TNF antibodies (25)), and receptors (soluble CD14, IL-1 receptor antagonist (26), antibodies against LBP), but the initial clinical data are merely disappointing.Lipoproteins are suggested to play an important role in the protection against infection and inflammation. All lipoproteins (high density lipoproteins (HDL), low-density lipoproteins (LDL), lipoprotein(a), very-low-density lipoproteins (VLDL), and chylomic...

Activated glial cells crucially contribute to brain inflammatory responses. Interleukin-10 (IL-10) is an important modulator of glial cell responses in the brain. In the present study we describe the expression of IL-10 and the IL-10 receptor (IL-10R1) in primary cocultures of rat microglial and astroglial cells. Using quantitative RT-PCR and ELISA, we show that IL-10 mRNA expression and subsequent IL-10 secretion is time-dependently induced by lipopolysaccharide (LPS). IL-10R1, however, is constitutively expressed in glial cell cocultures, as shown by RT-PCR and immunocytochemistry. Radioligand binding studies using 125I-IL-10 reveal that rat glial cells express a single binding site with an apparent affinity of approximately 600 pm for human IL-10. Observations in enriched cultures of either microglial or astroglial cells indicate that both cell types express IL-10 mRNA and are capable of secreting IL-10. Both cell types also express IL-10R1 mRNA and protein. However, in glial cell cocultures immunoreactive IL-10R1 protein is predominantly observed in astrocytes, suggesting that microglial expression of IL-10R1 in cocultures is suppressed by astrocytes. In addition, exogenous IL-10 is highly potent in down-regulating LPS-induced IL-1beta and IL-10 mRNA, and, at a higher dose, IL-10R1 mRNA in untreated and LPS-treated cultures, suggesting that IL-10 autoregulates its expression and inhibits that of IL-1beta at the transcriptional level. Together the findings support the concept that IL-10, produced by activated microglial and astroglial cells, modulates glia-mediated inflammatory responses through high-affinity IL-10 receptors via paracrine and autocrine interactions.

Abstract. Tissue-selective lymphocyte homing is directed in part by specialized vessels that define sites of lymphocyte exit from the blood. These vessels, the post capillary high endothelial venules (HEV), are found in organized lymphoid tissues, and at sites of chronic inflammation . Lymphocytes bearing specific receptors, called homing receptors, recognize and adhere to their putative ligands on high endothelial cells, the vascular addressins . After adhesion, lymphocytes enter organized lymphoid tissues by migrating through the endothelial cell wall . Cells and/or soluble factors arriving in lymph nodes by way of the afferent lymph supply have been implicated in the maintenance of HEV morphology and efficient lymphocyte homing . In the study reported here, we assessed the influence of afferent lymphatic vessel interruption on lymph node composition, organization of cellular elements; and on expression of vascular addressins. At 1 wk after occlusion of afferent lymphatic vessels, HEV became L PHOCYTES migrate continuously between various lymphoid and extra-lymphoid tissues of the body by way of the blood and lymph vascular systems. Lymphocyte entry into peripheral lymph nodes, mucosal lymphoid tissues, and sites of chronic inflammation is directed in part by tissue-selective interactions between blood-borne lymphocytes and specialized cells lining postcapillary high endothelial venules (HEV) . I Functional studies have revealed that lymphocyte adhesion to HEV is governed at the lymphocyte level by homing receptors (6,12,13,18), and at the endothelial cell level by vascular addressins (21,22). In the mouse system, two structurally and functionally distinct vascular addressins have been described. The peripheral lymph node addressin mediates the interaction of lymphocytes with HEV in peripheral lymphoid organs (22), and the mucosal addressin directs equivalent cellular interactions in mucosal lymphoid tissues (21). The peripheral lymph node and mucosal addressins are defined, and the adhesive interactions directed by these molecules are functionally flat walled and expression of the peripheral lymph node addressin disappeared from the luminal aspect of most vessels, while being retained on the abluminal side . In addition, an HEVspecific differentiation marker, defined by mAb MECA 325, was undetectable at 7-d postocclusion. In vivo homing studies revealed that these modified vessels support minimal lymphocyte traffic from the blood. After occlusion, we observed dramatic changes in lymphocyte populations and at 7-d postsurgery, lymph nodes were populated predominantly by cells lacking the peripheral lymph node homing receptor LECAM-1. In addition, effects on nonlymphoid cells were observed : subcapsular sinus macrophages, defined by mAb MOMA-1, disappeared ; and interdigitating dendritic cells, defined by mAb NLDC-145, were dramatically reduced. These data reveal that functioning afferent lymphatics are centrally involved in maintaining normal lymph node homeostasis.inhibited by the anti-addressin mAb and , res...

Microglia are important cells in the brain that can acquire different morphological and functional phenotypes dependent on the local situation they encounter. Knowledge on the region-specific gene signature of microglia may hold valuable clues for microglial functioning in health and disease, e.g., Parkinson’s disease (PD) in which microglial phenotypes differ between affected brain regions. Therefore, we here investigated whether regional differences exist in gene expression profiles of microglia that are isolated from healthy rat brain regions relevant for PD. We used an optimized isolation protocol based on a rapid isolation of microglia from discrete rat gray matter regions using density gradients and fluorescent-activated cell sorting. Application of the present protocol followed by gene expression analysis enabled us to identify subtle differences in region-specific microglial expression profiles and show that the genetic profile of microglia already differs between different brain regions when studied under control conditions. As such, these novel findings imply that brain region-specific microglial gene expression profiles exist that may contribute to the region-specific differences in microglia responsivity during disease conditions, such as seen in, e.g., PD.