p150/95 (CD11c/CD18) expression is required for the development of experimental autoimmune encephalomyelitis

CD11c is not required by microglia to convey neuroprotection after prion infection

Prion diseases are caused by the misfolding of a normal host protein that leads to gliosis, neuroinflammation, neurodegeneration, and death. Microglia have been shown to be critical for neuroprotection during prion infection of the central nervous system (CNS), and their presence extends survival in mice. How microglia impart these benefits to the infected host are unknown. Previous transcriptomics and bioinformatics studies suggested that signaling through the heterodimeric integrin receptor CD11c/CD18, expressed by microglia in the brain, might be important to microglial function during prion disease. Herein, we intracerebrally challenged CD11c-/- mice with prion strain RML and compared them to similarly infected C57BL/6 mice as controls. We initially assessed changes in the brain that are associated with disease such as astrogliosis, microgliosis, prion accumulation, and survival. Targeted qRT-PCR arrays were used to determine alterations in transcription in mice in response to prion infection. We demonstrate that expression of Itgax (CD11c) and Itgb2 (CD18) increases in the CNS in correlation with advancing prion infection. Gliosis, neuropathology, prion deposition, and disease progression in prion infected CD11c deficient mice were comparable to infected C57BL/6 mice. Additionally, both CD11c deficient and C57BL/6 prion-infected mouse cohorts had a similar consortium of inflammatory- and phagocytosis-associated genes that increased as disease progressed to clinical stages. Ingenuity Pathway Analysis of upregulated genes in infected C57BL/6 mice suggested numerous cell-surface transmembrane receptors signal through Spleen Tyrosine Kinase, a potential key regulator of phagocytosis and innate immune activation in the prion infected brain. Ultimately, the deletion of CD11c did not influence prion pathogenesis in mice and CD11c signaling is not involved in the neuroprotection provided by microglia, but our analysis identified a conspicuous phagocytosis pathway in the CNS of infected mice that appeared to be activated during prion pathogenesis.

Optical coherence tomography monitoring and diagnosing retinal changes in multiple sclerosis

This study explores the use of optical coherence tomography (OCT) to monitor and diagnose multiple sclerosis (MS). The analysis of reduced total macular volume and peripapillary retinal nerve fiber layer thinning are shown. The severity of these defects increases as MS progresses, reflecting the progressive degeneration of nerve fibers and retinal ganglion cells. The OCT parameters are noninvasive, sensitive indicators that can be used to assess the progression of neurodegeneration and inflammation in MS.

γδ T Cells Participating in Nervous Systems: A Story of Jekyll and Hyde

γδ T cells are distributed in various lymphoid and nonlymphoid tissues, and act as early responders in many conditions. Previous studies have proven their significant roles in infection, cancer, autoimmune diseases and tissue maintenance. Recently, accumulating researches have highlighted the crosstalk between γδ T cells and nervous systems. In these reports, γδ T cells maintain some physiological functions of central nervous system by secreting interleukin (IL) 17, and neurons like nociceptors can in turn regulate the activity of γδ T cells. Moreover, γδ T cells are involved in neuroinflammation such as stroke and multiple sclerosis. This review illustrates the relationship between γδ T cells and nervous systems in physiological and pathological conditions.

Alterations in peripheral blood monocyte and dendritic cell subset homeostasis in relapsing-remitting multiple sclerosis patients

Antigen-presenting cells participate and are implicated in the pathogenesis of multiple sclerosis. In our study we assessed the frequency of plasmacytoid (pDC) and myeloid (mDC) dendritic cells and the classical, intermediate and non-classical monocytes subsets, as well as their phenotypic and functional profile. We evaluated peripheral blood from relapsing-remitting patients treated with IFN-β in remission and relapse phases and from healthy subjects. In remission, we observed a decrease of mDC/pDC ratio and a return to normal values in relapse. In both phases the frequency of non-classical monocytes decreases. Concerning the phenotypic characterization, an increased HLA-DR expression was observed in remission and a decrease in relapse, revealing alterations in monocytes and dendritic cells homeostasis.

Complement-dependent synapse loss and microgliosis in a mouse model of multiple sclerosis

Multiple sclerosis (MS) is an inflammatory, neurodegenerative disease of the CNS characterized by both grey and white matter injury. Microglial activation and a reduction in synaptic density are key features of grey matter pathology that can be modeled with MOG_35-55 experimental autoimmune encephalomyelitis (EAE). Complement deposition combined with microglial engulfment has been shown during normal development and in disease as a mechanism for pruning synapses. We tested whether there is excess complement production in the EAE hippocampus and whether complement-dependent synapse loss is a source of degeneration in EAE using C1qa and C3 knockout mice. We found that C1q and C3 protein and mRNA levels were elevated in EAE mice. Genetic loss of C3 protected mice from EAE-induced synapse loss, reduced microglial activation, decreased the severity of the EAE clinical score, and protected memory/freezing behavior after contextual fear conditioning. C1qa KO mice with EAE showed little to no change on these measurements compared to WT EAE mice. Thus, pathologic expression and activation of the early complement pathway, specifically at the level of C3, contributes to hippocampal grey matter pathology in the EAE.

Epigenetic activation of O-linked β-N-acetylglucosamine transferase overrides the differentiation blockage in acute leukemia

Background

Overriding the differentiation blockage in acute myeloid leukemia (AML) is the most successful mode-of-action in leukemia therapy – now curing the vast majority of patients with acute promyelocytic leukemia (APL) using all-trans retinoic acid (ATRA)-based regimens. Similar approaches in other leukemia subtypes, such as IDH1/2-mutated AML, are under active investigation. We herein present successful release of the differentiation blockage upon treatment with the natural (−)-Δ⁹-Tetrahydrocannabinol isomer dronabinol in vitro and in vivo.

Methods

Cellular maturation and differentiation were followed in two patients employing whole genome methylation profiling, proteome analyses, NGS deep sequencing and multispectral imaging flow cytometry. For functional studies lentiviral OGT knock-down in vitro and ex vivo cell models were created to evaluate proliferative, apoptotic and differentiating effects of OGT in acute leukemia.

Findings

In here, we provide molecular evidence that dronbinol is capable to override the differentiation blockage of acute leukemia blasts at the state of the leukemia-initiating clone. We further identify the O-linked β-N-acetyl glucosamine (O-GlcNAc) transferase (OGT) to be crucial in this process. OGT is a master regulator enzyme adding O-GlcNAc to serine or threonine residues in a multitude of target proteins. Aberrant O-GlcNAc modification is implicated in pathologies of metabolic, neurodegenerative and autoimme diseases as well as cancers. We provide evidence that dronabinol induces transcription of OGT via epigenetic hypomethylation of the transcription start site (TSS). A lentiviral OGT-knock out approach proves the central role of OGT exerting antileukemic efficacy via a dual-mechanism of action: High concentrations of dronabinol result in induction of apoptosis, whereas lower concentrations drive cellular maturation. Most intriguingly, overriding of the differentiation blockage of acute leukemia blasts is validated in vivo following two patients treated with dronabinol.

Interpretation

In conclusion, we provide evidence for overcoming the differentiation blockage in acute leukemia in subentities beyond promyelocytic and IDH1/2-mutated leukemia and thereby identify O-GlcNAcylation as a novel (drugable) field for future leukemia research.

Funding

Unrestricted grant support by the IZKF Program of the Medical Faculty Tübingen (MMS) and Brigitte Schlieben-Lange Program as well as the Margarete von Wrangell Program of the Ministry of Science, Research and the Arts, Baden-Württemberg, Germany (KKS) and Athene Program of the excellence initiative University of Tübingen (KKS).

Complement: Bridging the innate and adaptive immune systems in sterile inflammation

The complement system is a collection of soluble and membrane-bound proteins that together act as a powerful amplifier of the innate and adaptive immune systems. Although its role in infection is well established, complement is becoming increasingly recognized as a key contributor to sterile inflammation, a chronic inflammatory process often associated with noncommunicable diseases. In this context, damaged tissues release danger signals and trigger complement, which acts on a range of leukocytes to augment and bridge the innate and adaptive immune systems. Given the detrimental effect of chronic inflammation, the complement system is therefore well placed as an anti-inflammatory drug target. In this review, we provide a general outline of the sterile activators, effectors, and targets of the complement system and a series of examples (i.e., hypertension, cancer, allograft transplant rejection, and neuroinflammation) that highlight complement's ability to bridge the 2 arms of the immune system.

γδ T lymphocytes in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis

The aim of the current review is to summarize the results of studies on the role of γδ T cells in the pathogenesis of multiple sclerosis and its animal model - the experimental autoimmune encephalomyelitis. Despite the fact that numerous studies have been performed, the role of γδ T is still not fully understood. It seems that there are two distinct subpopulations - one exacerbating the disease (IL-17-producing) and the other playing a protective role (IFN-γ-secreting). Nevertheless, future studies are required for an understanding of γδ T cells role in multiple sclerosis.

Th17 cells, γδ T cells and their interplay in EAE and multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis (MS) that shares many features with the human disease. This review will focus on the role of IL-17-secreting CD4 and γδ T cells in EAE and MS, the plasticity of Th17 cells in vivo and the application of these findings to the understating of the pathogenesis and the development of new treatments for MS. There is convincing evidence that IL-17-secreting CD4 T cells (Th17 cells) and IL-17-secreting γδ T cells play a critical pathogenic role in central nervous system (CNS) inflammation in EAE and MS. Indeed a significant number of the major discoveries on the pathogenic role of IL-17-secreting T cells in autoimmunity were made in the EAE model. These included the first demonstration that IL-23-activated IL-17-secreting T cells are the key T cells in driving autoimmune disease pathology. Although the early studies on IL-17 focused on Th17 cells, it was later demonstrated that γδ T cells were an important early source of IL-17 and IL-21 that helped amplify IL-17 production by Th17 cells in autoimmune diseases. Furthermore, it emerged that Th1 cells can also have encephalitogenic activity and that there was considerable plasticity in these T cell responses, with Th17 cells reverting to a Th1 phenotype in vivo. This questioned the pathogenic role of IL-17 and suggested that other cytokines, such as IFN-γ, GM-CSF and TNF, may be important. Nevertheless, biological drugs that target the IL-23-IL-17 pathway are highly effective in treating human psoriasis and are showing promise in the treatment of relapsing remitting MS and other T-cell mediated autoimmune diseases.

Non-identical twins: Different faces of CR3 and CR4 in myeloid and lymphoid cells of mice and men

Integrins are cell membrane receptors that are involved in essential physiological and serious pathological processes. Their main role is to ensure a closely regulated link between the extracellular matrix and the intracellular cytoskeletal network enabling cells to react to environmental stimuli. Complement receptor type 3 (CR3, αMβ₂, CD11b/CD18) and type 4 (CR4, αXβ₂, CD11c/CD18) are members of the β₂-integrin family expressed on most white blood cells. Both receptors bind multiple ligands like iC3b, ICAM, fibrinogen or LPS. β₂-integrins are accepted to play important roles in cellular adhesion, migration, phagocytosis, ECM rearrangement and inflammation. Several pathological conditions are linked to the impaired functions of these receptors. CR3 and CR4 are generally thought to mediate overlapping functions in monocytes, macrophages and dendritic cells, therefore the potential distinctive role of these receptors has not been investigated so far in satisfactory details. Lately it has become clear that a functional segregation has evolved between the two receptors regarding phagocytosis, cellular adhesion and podosome formation. In addition to their tasks on myeloid cells, the expression and function of CR3 and CR4 on lymphocytes have also gained interest recently. The picture is further complicated by the fact that while these β₂-integrins are expressed by immune cells both in mice and humans, there are significant differences in their expression level, functions and the pathological consequences of genetic defects. Here we aim to summarize our current knowledge on CR3 and CR4 and highlight the functional differences between these receptors, involving their expression in myeloid and lymphoid cells of both men and mice.

Complement Receptors in Myeloid Cell Adhesion and Phagocytosis

Myeloid cells make extensive use of the complement system in the context of recruitment, phagocytosis, and other effector functions. There are several types of complement receptors on myeloid cells, including G protein-coupled receptors for localizing the source of complement activation, and three sets of type I transmembrane proteins that link complement to phagocytosis: complement receptor 1, having an extracellular domain with tandem complement regulatory repeats; complement receptors 3 and 4, which are integrin family receptors comprising heterodimers of type I transmembrane subunits; and VSIG4, a member of the Ig superfamily. This review will focus on the role of the different classes of complement receptors and how their activities are integrated in the setting of immune tolerance and inflammatory responses.

IKKβ-mediated inflammatory myeloid cell activation exacerbates experimental autoimmune encephalomyelitis by potentiating Th1/Th17 cell activation and compromising blood brain barrier

Background

The inflammatory myeloid cell activation is one of the hallmarks of experimental autoimmune encephalomyelitis (EAE), yet the in vivo role of the inflammatory myeloid cell activation in EAE has not been clearly resolved. It is well-known that IKK/NF-κB is a key signaling pathway that regulates inflammatory myeloid activation.

Methods

We investigated the in vivo role of inflammatory myeloid cell activation in myelin oligodendrocyte glycoprotein (MOG) peptides-induced EAE using myeloid cell type-specific ikkβ gene conditional knockout-mice (LysM-Cre/Ikkβ^F/F).

Results

In our study, LysM-Cre/Ikkβ^F/F mice had alleviated clinical signs of EAE corresponding to the decreased spinal demyelination, microglial activation, and immune cell infiltration in the spinal cord, compared to the wild-type mice (WT, Ikkβ^F/F). Myeloid ikkβ gene deletion significantly reduced the percentage of CD4⁺/IFN-γ⁺ (Th1) and CD4⁺/IL-17⁺ (Th17) cells but increased the percentages of CD4⁺/CD25⁺/Foxp3⁺ (Treg) cells in the spinal cord and lymph nodes, corresponding to the altered mRNA expression of IFN-γ, IL-17, IL-23, and Foxp3 in the spinal cords of LysM-Cre/Ikkβ^F/F EAE mice. Also, the beneficial effect of myeloid IKKβ deletion in EAE corresponded to the decreased permeability of the blood brain barrier (BBB).

Conclusions

Our findings strongly suggest that IKK/NF-kB-induced myeloid cell activation exacerbates EAE by activating Th1 and Th17 responses and compromising the BBB. The development of NF-κB inhibitory agents with high efficacy through specific targeting of IKKβ in myeloid cells might be of therapeutic potential in MS and other autoimmune disorders.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-016-0116-1) contains supplementary material, which is available to authorized users.

Expression of CD11c Is Associated with Unconventional Activated T Cell Subsets with High Migratory Potential

CD11c is an α integrin classically employed to define myeloid dendritic cells. Although there is little information about CD11c expression on human T cells, mouse models have shown an association of CD11c expression with functionally relevant T cell subsets. In the context of genital tract infection, we have previously observed increased expression of CD11c in circulating T cells from mice and women. Microarray analyses of activated effector T cells expressing CD11c derived from naïve mice demonstrated enrichment for natural killer (NK) associated genes. Here we find that murine CD11c+ T cells analyzed by flow cytometry display markers associated with non-conventional T cell subsets, including γδ T cells and invariant natural killer T (iNKT) cells. However, in women, only γδ T cells and CD8+ T cells were enriched within the CD11c fraction of blood and cervical tissue. These CD11c+ cells were highly activated and had greater interferon (IFN)-γ secretory capacity than CD11c- T cells. Furthermore, circulating CD11c+ T cells were associated with the expression of multiple adhesion molecules in women, suggesting that these cells have high tissue homing potential. These data suggest that CD11c expression distinguishes a population of circulating T cells during bacterial infection with innate capacity and mucosal homing potential.

Animal models of Multiple Sclerosis

Multiple Sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system (CNS) which involves a complex interaction between immune system and neural cells. Animal modeling has been critical for addressing MS pathogenesis. The three most characterized animal models of MS are (1) the experimental autoimmune/allergic encephalomyelitis (EAE); (2) the virally-induced chronic demyelinating disease, known as Theiler׳s murine encephalomyelitis virus (TMEV) infection and (3) the toxin-induced demyelination. All these models, in a complementary way, have allowed to reach a good knowledge of the pathogenesis of MS. Specifically, EAE is the model which better reflects the autoimmune pathogenesis of MS and is extremely useful to study potential experimental treatments. Furthermore, both TMEV and toxin-induced demyelination models are suitable for characterizing the role of the axonal injury/repair and the remyelination process in MS. In conclusion, animal models, despite their limitations, remain the most useful instrument for implementing the study of MS.

Multiple low-affinity interactions support binding of human osteopontin to integrin αXβ2

Integrin α(X)β(2) (also known as complement receptor 4, p150,95, or CD11c/CD18) is expressed in the cell membrane of myeloid leukocytes. α(X)β(2) has been reported to bind a large number of structurally unrelated ligands, often with a shared molecular character in the presence of polyanionic stretches in poorly folded proteins or glucosaminoglycans. Nevertheless, it is unclear what chemical sources of polyanionicity enable the binding by α(X)β(2). Osteopontin (OPN) is an intrinsically disordered protein, which facilitates phagocytosis via the integrin α(X)β(2). Unlike for other integrins, neither the RGD nor the SVVYGLR motifs account for this binding, and the molecular basis of OPN binding by α(X)β(2) remains uncharacterized. Here, we show that the monovalent interactions between the ligand-binding domain of α(X)β(2) and OPN, its fragments, or caseins are weak, with dissociation constants higher than 10(-5)M but with high apparent stoichiometries. From comparison with cell adhesion studies, the discrimination between α(X)β(2) ligands and non-ligands appears to rely on these apparent stoichiometries in a way, which involves glutamate rather than aspartate side chains. Surprisingly, the extensive, negatively charged phosphorylation of OPN is not contributing to α(X)β(2) binding. Furthermore, synchrotron radiation circular spectroscopy excludes that the phosphorylation affects the general folding of OPN. Taken together, our quantitative analyses reveal a mode of ligand recognition by integrin α(X)β(2), which seem to differ in principles considerably from other OPN receptors.

Leukocyte integrins: role in leukocyte recruitment and as therapeutic targets in inflammatory disease

Infection or sterile inflammation triggers site-specific attraction of leukocytes. Leukocyte recruitment is a process comprising several steps orchestrated by adhesion molecules, chemokines, cytokines and endogenous regulatory molecules. Distinct adhesive interactions between endothelial cells and leukocytes and signaling mechanisms contribute to the temporal and spatial fine-tuning of the leukocyte adhesion cascade. Central players in the leukocyte adhesion cascade include the leukocyte adhesion receptors of the β2-integrin family, such as the αLβ2 and αMβ2 integrins, or of the β1-integrin family, such as the α4β1-integrin. Given the central involvement of leukocyte recruitment in different inflammatory and autoimmune diseases, the leukocyte adhesion cascade in general, and leukocyte integrins in particular, represent key therapeutic targets. In this context, the present review focuses on the role of leukocyte integrins in the leukocyte adhesion cascade. Experimental evidence that has implicated leukocyte integrins as targets in animal models of inflammatory disorders, such as experimental autoimmune encephalomyelitis, psoriasis, inflammatory bone loss and inflammatory bowel disease as well as preclinical and clinical therapeutic applications of antibodies that target leukocyte integrins in various inflammatory disorders are presented. Finally, we review recent findings on endogenous inhibitors that modify leukocyte integrin function, which could emerge as promising therapeutic targets.

Using EAE to better understand principles of immune function and autoimmune pathology

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) in which myelin becomes the target of attack by autoreactive T cells. The immune components of the disease are recapitulated in mice using the experimental autoimmune encephalomyelitis (EAE) model. EAE is classically induced by the immunization of mice with encephalitogenic antigens derived from CNS proteins such as proteolipid protein (PLP), myelin basic protein (MBP) and myelin oligodendrocyte glycoprotein (MOG). Immunization of susceptible mouse strains with these antigens will induce autoreactive inflammatory T cell infiltration of the CNS. More recently, the advent of clonal T cell receptor transgenic mice has led to the development of adoptive transfer protocols in which myelin-specific T cells may induce disease upon transfer into naïve recipient animals. When used in concert with gene knockout strains, these protocols are powerful tools by which to dissect the molecular pathways that promote inflammatory T cells responses in the central nervous system (CNS). Further, myelin-antigen-specific transgenic T cells may be cultured in vitro under a variety of conditions prior to adoptive transfer, allowing one to study the effects of soluble factors or pharmacologic compounds on T cell pathogenicity. In this review, we describe many of the existing models of EAE, and discuss the contributions that use of these models has made in understanding both T helper cell differentiation and the function of inhibitory T cell receptors. We focus on the  step-by-step elucidation of the network of signals required for T helper 17 (Th17) cell differentiation, as well as the molecular dissection of the Tim-3 negative regulatory signaling pathway in Th1 cells.

Targeted inhibition of complement using complement receptor 2-conjugated inhibitors attenuates EAE

Multiple sclerosis (MS) is the most common autoimmune demyelinating disease, affecting millions of individuals worldwide. In the last two decades, many therapeutic options for the treatment of MS have become available, however they are limited in terms of effectiveness and some remain plagued by safety issues. The currently available treatment options target relapsing remitting forms of MS and are not effective against the more progressive forms of the disease. These limitations highlight a significant unmet treatment need for MS. In experimental autoimmune encephalomyelitis (EAE) studies from our laboratory, we have previously shown, using a number of complement mutant and transgenic mice, that inhibition of the alternative complement pathway and the C3 convertase confers significant protection from disease. We report here that targeted inhibition of complement activation using complement receptor 2 (CR2)-conjugated inhibitors significantly attenuates EAE. Administration of CR2-Crry (blocks all complement pathways at C3 activation) and CR2-fH (specifically blocks the alternative pathway) just prior to and during the onset of EAE blocks progression of both acute and chronic disease. These data indicate that inhibition of complement may offer an effective therapeutic approach to treating both acute and chronic forms of demyelinating disease through blocking the alternative pathway or complement convertases.

The leucocyte β2 (CD18) integrins: the structure, functional regulation and signalling properties

Leucocytes are highly motile cells. Their ability to migrate into tissues and organs is dependent on cell adhesion molecules. The integrins are a family of heterodimeric transmembrane cell adhesion molecules that are also signalling receptors. They are involved in many biological processes, including the development of metazoans, immunity, haemostasis, wound healing and cell survival, proliferation and differentiation. The leucocyte-restricted β2 integrins comprise four members, namely αLβ2, αMβ2, αXβ2 and αDβ2, which are required for a functional immune system. In this paper, the structure, functional regulation and signalling properties of these integrins are reviewed.

Gut mucosal injury in neonates is marked by macrophage infiltration in contrast to pleomorphic infiltrates in adult: evidence from an animal model

Necrotizing enterocolitis (NEC) is an inflammatory bowel necrosis of premature infants. In tissue samples of NEC, we identified numerous macrophages and a few neutrophils but not many lymphocytes. We hypothesized that these pathoanatomic characteristics of NEC represent a common tissue injury response of the gastrointestinal tract to a variety of insults at a specific stage of gut development. To evaluate developmental changes in mucosal inflammatory response, we used trinitrobenzene sulfonic acid (TNBS)-induced inflammation as a nonspecific insult and compared mucosal injury in newborn vs. adult mice. Enterocolitis was induced in 10-day-old pups and adult mice (n = 25 animals per group) by administering TNBS by gavage and enema. Leukocyte populations were enumerated in human NEC and in murine TNBS-enterocolitis using quantitative immunofluorescence. Chemokine expression was measured using quantitative polymerase chain reaction, immunoblots, and immunohistochemistry. Macrophage recruitment was investigated ex vivo using intestinal tissue-conditioned media and bone marrow-derived macrophages in a microchemotaxis assay. Similar to human NEC, TNBS enterocolitis in pups was marked by a macrophage-rich leukocyte infiltrate in affected tissue. In contrast, TNBS-enterocolitis in adult mice was associated with pleomorphic leukocyte infiltrates. Macrophage precursors were recruited to murine neonatal gastrointestinal tract by the chemokine CXCL5, a known chemoattractant for myeloid cells. We also demonstrated increased expression of CXCL5 in surgically resected tissue samples of human NEC, indicating that a similar pathway was active in NEC. We concluded that gut mucosal injury in the murine neonate is marked by a macrophage-rich leukocyte infiltrate, which contrasts with the pleomorphic leukocyte infiltrates in adult mice. In murine neonatal enterocolitis, macrophages were recruited to the inflamed gut mucosa by the chemokine CXCL5, indicating that CXCL5 and its cognate receptor CXCR2 merit further investigation as potential therapeutic targets in NEC.

Prevention of experimental cerebral malaria by Flt3 ligand during infection with Plasmodium berghei ANKA

Dendritic cells are the most potent antigen-presenting cells, but their roles in blood-stage malaria infection are not fully understood. We examined the effects of Flt3 ligand, a cytokine that induces dendritic cell production, in vivo on the course of infection with Plasmodium berghei ANKA. Mice treated with Flt3 ligand showed preferential expansion of CD8(+) dendritic cells and granulocytes, as well as lower levels of parasitemia, and were protected from the development of lethal experimental cerebral malaria (ECM). Rag2 knockout mice treated with Flt3 ligand also showed inhibition of parasitemia, suggesting that this protection was due, at least in part, to the stimulation of innate immunity. However, it was unlikely that the inhibition of ECM was due simply to the reduction in the level of parasitemia. In the peripheral T cell compartment, CD8(+) T cell levels were markedly increased in Flt3 ligand-treated mice after infection. These CD8(+) T cells expressed CD11c and upregulated CXCR3, while the expression of CD137, CD25, and granzyme B was reduced. In the brain, the number of sequestered CD8(+) T cells was not significantly different for treated versus untreated mice, while the proportion of CD8(+) T cells that produce gamma interferon (IFN-γ) and granzyme B was significantly reduced in treated mice. In addition, sequestration of parasitized red blood cells (RBCs) in the brain was reduced, suggesting that altered CD8(+) T cell activation and reduced sequestration of parasitized RBCs culminated in inhibition of ECM development. These results suggest that the quantitative and qualitative changes in the dendritic cell compartment are important for the pathogenesis of ECM.

Absence of β2 integrins impairs regulatory T cells and exacerbates CD4+ T cell-dependent autoimmune carditis

The immunopathogenic mechanisms mediating inflammation in multiorgan autoimmune diseases may vary between the different target tissues. We used the K/BxN TCR transgenic mouse model to investigate the contribution of CD4(+) T cells and β(2) integrins in the pathogenesis of autoimmune arthritis and endocarditis. Depletion of CD4(+) T cells following the onset of arthritis specifically prevented the development of cardiac valve inflammation. Genetic absence of β(2) integrins had no effect on the severity of arthritis and unexpectedly increased the extent of cardiovascular pathology. The exaggerated cardiac phenotype of the β(2) integrin-deficient K/BxN mice was accompanied by immune hyperactivation and was linked to a defect in regulatory T cells. These findings are consistent with a model in which the development of arthritis in K/BxN mice relies primarily on autoantibodies, whereas endocarditis depends on an additional contribution of effector T cells. Furthermore, strategies targeting β(2) integrins for the treatment of systemic autoimmune conditions need to consider not only the role of these molecules in leukocyte recruitment to sites of inflammation, but also their impact on the regulation of immunological tolerance.

CD11c controls herpes simplex virus 1 responses to limit virus replication during primary infection

CD11c is expressed on the surface of dendritic cells (DCs) and is one of the main markers for identification of DCs. DCs are the effectors of central innate immune responses, but they also affect acquired immune responses to infection. However, how DCs influence the efficacy of adaptive immunity is poorly understood. Here, we show that CD11c(+) DCs negatively orchestrate both adaptive and innate immunity against herpes simplex virus type 1 (HSV-1) ocular infection. The effectiveness and quantity of virus-specific CD8(+) T cell responses are increased in CD11c-deficient animals. In addition, the levels of CD83, CD11b, alpha interferon (IFN-α), and IFN-β, but not IFN-γ, were significantly increased in CD11c-deficient animals. Higher levels of IFN-α, IFN-β, and CD8(+) T cells in the CD11c-deficient mice may have contributed to lower virus replication in the eye and trigeminal ganglia (TG) during the early period of infection than in wild-type mice. However, the absence of CD11c did not influence survival, severity of eye disease, or latency. Our studies provide for the first time evidence that CD11c expression may abrogate the ability to reduce primary virus replication in the eye and TG via higher activities of type 1 interferon and CD8(+) T cell responses.

Macrophages counteract demyelination in a mouse model of globoid cell leukodystrophy

Whether microglia and macrophages are beneficial or harmful in many neurological disorders, including demyelinating diseases such as multiple sclerosis and the leukodystrophies, is currently under debate. Answering this question is of special interest in globoid cell leukodystrophy (GLD), a genetic fatal demyelinating disease, because its rapidly progressive demyelination in the nervous system is accompanied by a characteristic accumulation of numerous globoid macrophages. Therefore, we cross-bred the twitcher (twi) mouse, a bona fide model of GLD, with the macrophage-deficient osteopetrotic mutant and studied the resultant macrophage-deficient twitcher (twi+op) mouse. The twi+op mouse had few microglia and macrophages in the white matter and, interestingly, showed a more severe clinical phenotype compared to the twi mouse. The number of nonmyelinated axons in the spinal cord was significantly higher in twi+op mice than in twi mice at 45 d old. The difference appeared to be due to impaired remyelination in twi+op mice rather than accelerated demyelination. Quantitative reverse transcription PCR and immunohistochemical studies revealed that the recruitment of oligodendrocyte progenitor cells in response to demyelination was compromised in twi+op mice. Increased myelin debris in the white matter parenchyma of twi+op mice suggested that phagocytosis by macrophages may play an important role in promoting remyelination. Macrophage markers for both protective and destructive phenotypes were significantly upregulated in the spinal cord of twi mice but were close to normal in twi+op mice due to the reduced macrophage number. The overall effects of macrophages in GLD appear to be beneficial to myelin by promoting myelin repair.

Cancer dissemination--lessons from leukocytes

Cancer cells can move through tissues in a variety of different ways. In some cases, an epithelial-to-mesenchymal transition enables cancer cells to acquire fibroblast-like migratory properties. However, it is also becoming apparent that some cancer cells move in an amoeboid way similar to leukocytes. This theme will be the focus of the review, where we will discuss the similarities and differences between the mechanisms used by cancer cells and leukocytes to cross parenchymal basement membranes, move through interstitial tissue, and enter and exit the vasculature. Further, we propose that the ability to switch between different migratory mechanisms is critical for cells to relocate from one tissue to another.

Alpha4beta1 integrin mediates the recruitment of immature dendritic cells across the blood-brain barrier during experimental autoimmune encephalomyelitis

Dendritic cells (DCs) within the CNS are recognized to play an important role in the effector phase and propagation of the immune response in experimental autoimmune encephalomyelitis (EAE), a mouse model for multiple sclerosis. However, the mechanisms regulating DC trafficking into the CNS still need to be characterized. In this study, we show by performing intravital fluorescence videomicroscopy of the inflamed spinal cord white-matter microvasculature in SJL mice with EAE that immature, and to a lesser extent, LPS-matured, bone marrow-derived DCs efficiently interact with the CNS endothelium by rolling, capturing, and firm adhesion. Immature but not LPS-matured DCs efficiently migrated across the wall of inflamed parenchymal microvessels into the CNS. Blocking alpha4 integrins interfered with the adhesion but not the rolling or capturing of immature and LPS-matured DCs to the CNS microvascular endothelium, inhibiting their migration across the vascular wall. Functional absence of beta1 integrins but not of beta7 integrins or alpha4beta7 integrin similarly reduced the adhesion of immature DCs to the CNS microvascular endothelium, demonstrating that alpha4beta1 but not alpha4beta7 integrin mediates this step of immature DCs interaction with the inflamed blood-brain barrier during EAE. Our study shows that during EAE, especially immature DCs migrate into the CNS, where they may be crucial for the perpetuation of the CNS-targeted autoimmune response. Thus therapeutic targeting of alpha4 integrins affects DC trafficking into the CNS and may therefore lead to the resolution of the CNS autoimmune inflammation by reducing the number of CNS professional APCs.

Myelin basic protein priming reduces the expression of Foxp3 in T cells via nitric oxide

Regulatory T cells (Tregs) play a vital role in autoimmune disorders. Among several markers, forkhead box p3 (Foxp3) is the most specific with regard to Treg activity. Therefore, understanding mechanisms that regulate Foxp3 expression is a critical step for unraveling the complicacy of autoimmune pathophysiology. The present study was undertaken to investigate the crosstalk between NO and Tregs. Interestingly, after myelin basic protein (MBP) priming, the expression of Foxp3 decreased in MBP-primed T cells. However, blocking NO either by inhibiting inducible NO synthase with l-N(6)-(1-iminoethyl)-lysine hydrochloride or through scavenging with PTIO or by pharmacological drugs, such as pravastatin, sodium benzoate, or gemfibrozil, restored the expression of Foxp3 in MBP-primed T cells. However, this restoration of Foxp3 by pharmacological drugs was reversed by S-nitrosoglutathione, an NO donor. Similarly, NO also decreased the populations of Tregs characterized by CD4(+)CD25(+) and CD25(+)FoxP3(+) phenotypes. We have further confirmed this inverse relationship between NO and Foxp3 by analyzing the mRNA expression of Foxp3 and characterizing CD25(+)FoxP3(+) or CD4(+)Foxp3(+) phenotypes from inducible NO synthase knockout mice. Moreover, this inverse relation between NO and Foxp3 also was observed during priming with myelin oligodendrocyte glycoprotein, another target neuroantigen in multiple sclerosis, as well as collagen, a target autoantigen in rheumatoid arthritis. Finally, we demonstrate that NO inhibited the expression of Foxp3 in MBP-primed T cells via soluble guanylyl cyclase-mediated production of cGMP. Taken together, our data imply a novel role of NO in suppressing Foxp3(+) Tregs via the soluble guanylyl cyclase pathway.

beta2-integrins in demyelinating disease: not adhering to the paradigm

The beta(2)-integrins are a subfamily of integrins expressed on leukocytes that play an essential role in leukocyte trafficking, activation, and many other functions. Studies in EAE, the animal model for multiple sclerosis, show differential requirements for beta(2)-integrins in this disease model, ranging from critical in the case of LFA-1 (CD11a/CD18) to unimportant in the case of CD11d/CD18. Importantly, expression of beta(2)-integrins on T cell subsets provides some clues as to the function(s) these adhesion molecules play in disease development. For example, transferred EAE studies have shown that Mac-1 (CD11b/CD18) expression on alphabeta T cells is critical for disease development, and the absence of LFA-1 on Tregs in recipient mice results in exacerbated disease. In this review, we summarize recent findings regarding the role of beta(2)-integrins in demyelinating disease and new information about the role of beta(2)-integrins with respect to alterations in Treg numbers and function. In addition, we discuss the potential for targeting beta(2)-integrins in human demyelinating disease in light of the recent animal model studies.

CD11c expression in adipose tissue and blood and its role in diet-induced obesity

OBJECTIVE

To examine CD11c, a beta(2)-integrin, on adipose tissue (AT) leukocytes and blood monocytes and its role in diet-induced obesity.

METHODS AND RESULTS

High-fat diet-induced obese C57BL/6 mice, CD11c-deficient mice, and obese humans were studied. CD11c, leukocytes, and chemokines/cytokines were examined in AT and/or blood by flow cytometry, RNase protection assay, quantitative polymerase chain reaction, or enzyme-linked immunosorbent assay. Obese C57BL/6 mice had increased CD11c in AT and blood compared with lean controls. CD11c messenger RNA positively correlated with monocyte chemoattractant protein 1 in human visceral AT. Obese humans with metabolic syndrome had a higher CD11c level on blood monocytes compared with lean humans. Low-fat diet-induced weight loss reduced blood monocyte CD11c in obese mice and humans. Mouse and human monocyte CD11c levels and mouse AT CD11c messenger RNA correlated with insulin resistance. CD11c deficiency in mice did not alter weight gain but decreased inflammation, evidenced by a lower T-cell number and reduced levels of major histocompatibility complex class II, C-C chemokine ligand 2 (CCL5), CCL4, and interferon gamma in AT, and ameliorated insulin resistance and glucose intolerance associated with diet-induced obesity.

CONCLUSIONS

Diet-induced obesity increased CD11c in both AT and blood in mice and humans. CD11c plays an important role in T-cell accumulation and activation in AT, and contributes to insulin resistance associated with obesity.

Gammadelta T cells in EAE: early trafficking events and cytokine requirements

We have previously shown that gammadelta T cells traffic to the CNS during EAE with concurrently increased expression of beta(2)-integrins and production of IFN-gamma and TNF-alpha. To extend these studies, we transferred bioluminescent gammadelta T cells to WT mice and followed their movement through the acute stages of disease. We found that gammadelta T cells rapidly migrated to the site of myelin oligodendrocyte glycoprotein peptide injection and underwent massive expansion. Within 6 days after EAE induction, bioluminescent gammadelta T cells were found in the spinal cord and brain, peaking in number between days 10 and 12 and then rapidly declining by day 15. Reconstitution of gammadelta T cell(-/-) mice with gammadelta T cells derived from beta(2)-integrin-deficient mice (CD11a, -b or -c) demonstrated that gammadelta T-cell trafficking to the CNS during EAE is independent of this family of adhesion molecules. We also examined the role of gammadelta T-cell-produced IFN-gamma and TNF-alpha in EAE and found that production of both cytokines by gammadelta T cells was required for full development of EAE. These results indicate that gammadelta T cells are critical for the development of EAE and suggest a therapeutic target in demyelinating disease.

Deficiency of thrombospondin-1 reduces Th17 differentiation and attenuates experimental autoimmune encephalomyelitis

Transforming growth factor beta (TGF-beta) plays a role both in the induction of Treg and in the differentiation of the IL-17-secreting T cells (Th17) which drive inflammation in experimental autoimmune encephalomyelitis (EAE). We investigated the role that thrombospondin-1 (TSP-1) dependent activation of TGF-beta played in the generation of an encephalitic Th17 response in EAE. Upon immunization with myelin oligodendrocyte glycoprotein peptide (MOG(35-55)), TSP-1 deficient (TSP-1(null)) mice and MOG(35-55) TCR transgenic mice that lack of TSP-1 (2D2 x TSP-1(null)) exhibited an attenuated form of EAE, and secreted lower levels of IL-17. Adoptive transfer of in vitro-activated 2D2 x TSP-1(null) T cells induced a milder form of EAE, independent of TSP-1 expression in the recipient mice. Furthermore, in vitro studies demonstrated that anti-CD3/anti-CD28 pre-activated CD4+ T cells transiently upregulated latent TGF-beta in a TSP-1 dependent way, and such activation of latent TGF-beta was required for the differentiation of Th17 cells. These results demonstrate that TSP-1 participates in the differentiation of Th17 cells through its ability to activate latent TGF-beta, and enhances the inflammatory response in EAE.

Macrophages as APC and the dendritic cell myth

Dendritic cells have been considered an immune cell type that is specialized for the presentation of Ag to naive T cells. Considerable effort has been applied to separate their lineage, pathways of differentiation, and effectiveness in Ag presentation from those of macrophages. This review summarizes evidence that dendritic cells are a part of the mononuclear phagocyte system and are derived from a common precursor, responsive to the same growth factors (including CSF-1), express the same surface markers (including CD11c), and have no unique adaptation for Ag presentation that is not shared by other macrophages.

Effector and suppressor roles for LFA-1 during the development of experimental autoimmune encephalomyelitis

LFA-1 (CD11a/CD18) is a member of the beta(2)-integrin family of adhesion molecules important in leukocyte trafficking and activation. Although LFA-1 is thought to contribute to the development of experimental autoimmune encephalomyelitis (EAE) primarily through its functions on effector T cells, its importance on other leukocyte populations remains unexplored. To address this question, we performed both adoptive transfer EAE experiments involving CD11a(-/-) mice and trafficking studies using bioluminescent T cells expressing luciferase under the control of a CD2 promoter (T-lux cells). Transfer of encephalitogenic CD11a(-/-) T cells to wild type mice resulted in a significant reduction in overall EAE severity compared to control transfers. We also observed, using in vivo imaging techniques, that CD11a(-/-) T-lux cells readily infiltrated lymph nodes and the CNS of wild type recipients with kinetics comparable to CD11a(+/+) transfers, although their overall numbers in these organs were reduced. Surprisingly, transfer of encephalitogenic wild type T cells to CD11a(-/-) mice induced a severe and sometimes fatal EAE disease course, associated with massive T cell infiltration and proliferation in the CNS. These data indicate that LFA-1 expression on leukocytes in recipient mice plays an important immunomodulatory role in EAE. Thus, LFA-1 acts as a key regulatory adhesion molecule during the development of EAE, serving both pro- and anti-inflammatory roles in disease pathogenesis.

The complement cascade: Yin-Yang in neuroinflammation--neuro-protection and -degeneration

The complement cascade has long been recognized to play a key role in inflammatory and degenerative diseases. It is a 'double edged' sword as it is necessary to maintain health, yet can have adverse effects when unregulated, often exacerbating disease. The contrasting effects of complement, depending on whether in a setting of health or disease, is the price paid to achieve flexibility in scope and degree of a protective response for the host from infection and injury. Loss or even decreased efficiency of critical regulatory control mechanisms can result in aggravated inflammation and destruction of self-tissue. The role of the complement cascade is poorly understood in the nervous system and neurological disorders. Novel studies have demonstrated that the expression of complement proteins in brain varies in different cell types and the effects of complement activation in various disease settings appear to differ. Understanding the functioning of this cascade is essential, as it has therapeutic implications. In this review, we will attempt to provide insight into how this complex cascade functions and to identify potential strategic targets for therapeutic intervention in chronic diseases as well as acute injury in the CNS.

Deletion of both ICAM-1 and C3 enhances severity of experimental autoimmune encephalomyelitis compared to C3-deficient mice

Multiple sclerosis (MS) is an autoimmune disease characterized by central nervous system (CNS) inflammation and leukocyte infiltration, demyelination of neurons, and blood-brain barrier breakdown. The development of experimental autoimmune encephalomyelitis (EAE), the animal model for MS is dependent on a number of components of the immune system including complement and adhesion molecules. Previous studies in our lab have examined the role of C3, the central complement component, and intercellular adhesion molecule-1 (ICAM-1) a key cell adhesion molecule involved in leukocyte trafficking to sites of inflammation including the CNS. In these studies we demonstrated that myelin oligodendrocyte glycoprotein (MOG)-induced EAE is markedly attenuated in both ICAM-1(-/-) and C3(-/-) mice. Given the pivotal role that these proteins play in EAE, we hypothesized that EAE in ICAM-1(-/-) and C3(-/-) double mutant mice would likely fail to develop. Unexpectedly, EAE in ICAM-1(-/-)xC3(-/-) mice was only modestly attenuated compared to wild type mice and significantly worse than C3(-/-) mice. Leukocyte infiltration was commensurate with disease severity between the three groups of mice. Spinal cord T cells from ICAM-1(-/-)xC3(-/-) mice produced the highest levels of IFN-gamma and TNF-alpha, despite reduced disease severity compared to wild type mice. The mechanisms behind the elevated EAE severity in ICAM-1(-/-)xC3(-/-) mice may relate to altered homing of leukocytes or processing of self-antigens in the double mutant background.

Differential expression of beta 2-integrins and cytokine production between gammadelta and alphabeta T cells in experimental autoimmune encephalomyelitis

The expression of beta 2-integrins on gammadelta T cells in naïve mice or those with experimental autoimmune encephalomyelitis (EAE) remains poorly characterized. We compared beta 2-integrin expression and cytokine production between gammadelta and alphabeta T cells over the acute course of EAE. We observed that unlike in alphabeta T cells, beta 2-integrin expression on gammadelta T cells increased significantly from baseline, peaked at Day 10, and remained unchanged in the draining lymph nodes or declined in the spleen and CNS by Day 15. In addition, IFN-gamma- and TNF-alpha-producing gammadelta T cells infiltrated the CNS rapidly and produced significantly more of these cytokines than alphabeta T cells throughout the course of EAE. These results suggest unique roles for beta 2-integrins in the trafficking of gammadelta versus alphabeta T cells during EAE and that gammadelta T cells infiltrate the CNS rapidly, producing cytokines, which modulate acute disease.