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Toll-like receptors are key players in neurodegeneration

The activation of innate immune response is initiated by engagement of pattern-recognition receptors (PPRs), such as Toll-like receptors (TLRs). These receptors are expressed in peripheral leukocytes and in many cell types in the central nervous system (CNS). The expression of TLRs in CNS was mainly studied in astrocytes and microglial cells. However, new evidence indicates that these receptors may play an important role in neuronal homeostasis. The expression of TLRs in the CNS is variable and can be modulated by multiple factors, including pro-inflammatory molecules, which are elevated in neurodegenerative diseases and can increase the expression of TLRs in CNS cells. Moreover, activation of TLRs induces the release of pro-inflammatory cytokines. Therefore, TLRs have been shown to play a role in several aspects of neurodegenerative diseases. Here we will discuss results reported in the recent literature concerning the participation of TLRs in neurodegenerative diseases.

Autophagy in inflammation, infection, neurodegeneration and cancer.

In its classical form, autophagy is an essential, homeostatic process by which cytoplasmic components are degraded in a double-membrane-bound autophagosome in response to starvation. Paradoxically, although autophagy is primarily a protective process for the cell, it can also play a role in cell death. The roles of autophagy bridge both the innate and adaptive immune systems and autophagic dysfunction is associated with inflammation, infection, neurodegeneration and cancer. In this review, we discuss the contribution of autophagy to inflammatory, infectious and neurodegenerative diseases, as well as cancer.

Granulocyte-macrophage colony-stimulating factor protects dendritic cells from liposome-encapsulated dichloromethylene diphosphonate-induced apoptosis through a Bcl-2-mediated pathway.

Liposome‐encapsulated dichloromethylene diphosphonate (L‐MDP) has been used for depleting cells of the monocyte‐macrophage lineage. We have undertaken this study to investigate whether dendritic cells are susceptible to this liposome‐encapsulated compound. Dendritic cells were cultured in the presence of L‐MDP and further processed for apoptosis detection. The highly characteristic DNA cleavage into oligonucleosome‐sized fragments, incorporation of biotinylated dUTP into DNA strand breaks and the typical ultrastructural features of apoptosis were evident in dendritic cells exposed to the drug. More importantly, we demonstrated that granulocyte‐macrophage colony‐stimulating factor protects dendritic cells not only from apoptosis induced by the exogenous compound but also from spontaneous apoptosis. Western blot analysis revealed that this protection was tightly correlated with the activation of a Bcl‐2‐mediated pathway. Regulation of the apoptotic threshold of dendritic cells will be advantageous for the generation of new insights in immunotherapy.

Interleukin 4 induces the apoptosis of mouse microglial cells by a caspase-dependent mechanism.

Microglial cells are resident macrophages in the central nervous system (CNS) and become activated in many pathological conditions. Activation of microglial cells results in reactive microgliosis, manifested by an increase in cell number in the affected CNS regions. The control of microgliosis may be important to prevent pathological damage to the brain. The type 2 cytokine IL-4 has been reported to be protective in brain inflammation. However, its effect on microglial cell survival was not well understood. In this study, we report a dual effect of IL-4 on the survival of mouse microglial cells. In a 6h short term culture, IL-4 reduced the death of microglial cells induced by staurosporine. In contrast, in long term treatment (more than 48h), IL-4 increased the apoptotic death of both primary mouse microglial cells and a microglial cell line N9. Mechanistic studies revealed that, in microglial cells, IL-4 increased the levels of cleaved caspase 3 and PARP, which is down-stream of activated caspase 3. In addition, IL-4 down regulated the autophagy and the antiapoptotic protein Bcl-xL in microglial cells. On the other hand, the pre-incubation of microglial cells with IL-4 for 24h, attenuated the cell death induced by the neurotoxic peptide amyloid beta 1-42 (Aβ42). Our observations demonstrate a novel function of IL-4 in regulating the survival of microglial cells, which may have important significance in reduction of undesired inflammatory responses in the CNS.

Activation of macrophages by silicones: phenotype and production of oxidant metabolites

BackgroundThe effect of silicones on the immune function is not fully characterized. In clinical and experimental studies, immune alterations associated with silicone gel seem to be related to macrophage activation. In this work we examined in vivo, phenotypic and functional changes on peritoneal macrophages early (24 h or 48 h) and late (45 days) after the intraperitoneal (i.p.) injection of dimethylpolysiloxane (DMPS) (silicone). We studied the expression of adhesion and co-stimulatory molecules and both the spontaneous and the stimulated production of reactive oxygen intermediates and nitric oxide (NO).ResultsThe results presented here demonstrate that the fluid compound DMPS induced a persistent cell recruitment at the site of the injection. Besides, cell activation was still evident 45 days after the silicone injection: activated macrophages exhibited an increased expression of adhesion (CD54 and CD44) and co-stimulatory molecules (CD86) and an enhanced production of oxidant metabolites and NO.ConclusionsSilicones induced a persistent recruitment of leukocytes at the site of the injection and macrophage activation was still evident 45 days after the injection.

Toll-like receptors and diseases

By the end of the 19th century, Dr. Elie Metchnikof proposed the theory of “microbial recognition” by innate immunity and phagocytosis trough his pioneering research into this field, for which he was awarded the Nobel Prize in 1908. In the late 1980s, Dr. Charles Janeway emphasized the importance of pathogen recognition as the first line of host defense. This established the concept of recognition of pathogen-associated molecular patterns (PAMPs) by patternrecognition receptors (PRRs) of the host. The past decade has witnessed a booming in the scope of studies of the mechanisms of naturally occurring innate immunity. The discovery of Toll-like receptors (TLRs) in the mid-1990s clearly showed that pathogen recognition by innate immune system is, in contrast to the traditional belief in its non-specificity, a precisely regulated and specific process mediated by germline-encoded PRRs that have evolved to detect PAMPs of foreign pathogens. Although TLRs have been implicated as the first line defense in human for anti-microbial responses, they are also involved in the development of many inflammatory and immune diseases not directly caused by bacterial or viral infection. Such properties of TLRs are attributed to their capacity to recognize hostderived agonists mostly released by damaged cells or tissues during the progression of diseases. The development of the research of TLRs in diseases has reached to the stage that a collection of comprehensive reviews of the progress should provide a platform for further discussion of the beneficial versus detrimental roles of these PRRs. Thus, this Special Issue contains articles contributed by investigators directly involved in the studies of TLRs during the past years. We hope the experiences and perspectives of the authors of various backgrounds will stimulate more in-depth studies by our readers both in or ready to be in the relevant field. Concerning TLRs as major portals for entry of microorganisms and allergens, Dr. K. Chen and co-workers [1] discuss the involvement of TLRs in the pathological processes of allergic airway inflammation in which dendritic cells (DCs) are preferential targets of PAMPs and TLR signaling in DCs determines the balance of Th1/Th2 polarization. In addition to DCs, airway epithelial cells, eosinophils and mast cells also express a variety of TLRs and contribute to allergic airway inflammation. For instance, activation of TLRs in mast cells and airway epithelial cells increase the release of proallergic Th2 cytokines. On the other hand, stimulation of TLR9 induces Th1 responses that may limit Th2dependent allergy. Moreover, activation of TLR4, TLR3 and TLR9 promotes DCs to release factors that skew a Th17 differentiation, which, while paradoxically, may exacerbate allergic airway inflammation, also could inhibit the production of Th2 cytokines in the airway, thus limiting the severity of the disease. Drs. Kovach and Standiford [2] provide an overview of the participation of TLRs in both infectious and non-infectious lung diseases. The lung is in contact with numerous infectious agents, foreign

Abrogation of TNFα Production during Cancer Immunotherapy Is Crucial for Suppressing Side Effects Due to the Systemic Expression of IL-12

For more than a decade, the cytokine interleukin-12 (IL-12) has been utilized, either alone or in combination with other drugs, as a treatment for cancer. The numerous anti-tumor properties of IL-12 still generate interest in the clinical use of this cytokine, even though it has demonstrated toxicity when administrated systemically. As an approach to overcome this toxicity, numerous laboratories have attempted to induce IL-12 expression at the site of the tumor. However for tumors that are difficult to remove surgically or for the treatment of disseminated metastases, systemic expression of this cytokine still remains as the most efficient method of administration. Nevertheless, finding alternative approaches for the use of IL-12 in the treatment of cancer and unraveling the basis of IL-12-side effects remain a challenge. In the present work we demonstrate that systemic expression of IL-12 through hydrodynamic injection of IL-12 cDNA is able to induce different types of liver lesions associated with a toxic pathology. However we report here that hepatic toxicity is diminished and survival of mice enhanced in the absence of tumor necrosis factor alpha (TNFα). This observation is in contrast to several murine models and clinical trials that postulate interferon gamma (IFNγ) as the main cytokine responsible for IL-12 toxicity. Moreover, our work demonstrates that when IL-12 cDNA is co-injected with IL-18 cDNA or when mice are pre-treated with a low dose of IL-12 cDNA prior to receiving a high dose of IL-12 cDNA, systemic levels of TNFα are almost completely abrogated, resulting in improved survival and less hepatic damage. Importantly, abrogation of TNFα signaling does not affect the strong anti-tumor activity of IL-12. Thus, neutralizing TNFα with antagonists already approved for human use offers a promising approach to abrogate IL-12 side effects during the use of this cytokine for the treatment of cancer.

Interaction of Bacterial Toxin with Leukocytes Measured by Flow Cytometry

Enterobacter cloacae toxin was purified in the form of monomer and polymer. Both forms stimulated the generation of reactive oxygen species (ROS) at sublytic concentration; the oxidative stress produced was studied by using chemiluminescence (CL). The alteration generated caused death of leukocytes, especially at high toxin concentration. Polymeric toxin produced more oxidative stress than the monomeric one. Cytometry allowed the detection of more toxin binding to neutrophils rather than to monocytes or lymphocytes. There was binding at 4°C, and the amount of toxin in the cells increased at 37°C. The interaction of toxin with leukocytes was evident even after 100°C treatment of toxin during 5 min. The incubation with 2-mercaptoethanol was not necessary for toxin binding.

Induction of autoimmune prostatitis using liposomes is associated to peritoneal cells activation

PROBLEM: Study and characterization of rat peritoneal cells (PC) involved in the induction of autoimmune prostatitis after the intraperitoneal administration of native extract of accessory glands (RAG) associated with liposomes (RAGL).

Characterization of an Immunoregulatory Cell Subset Involved in the Upregulation of the Autoimmune Response to Rat Male Accessory Glands

PROBLEM: We studied the regulation of the autoimmune response to rat male accessory glands (RAG) using liposomes as adjuvants.