Distinct roles for lymphotoxin-alpha and tumor necrosis factor in organogenesis and spatial organization of lymphoid tissue

Contribution of mast cell-derived interleukin-1β to uric acid crystal-induced acute arthritis in mice

OBJECTIVE

Gouty arthritis is caused by the precipitation of monosodium urate monohydrate (MSU) crystals in the joints. While it has been reported that mast cells (MCs) infiltrate gouty tophi, little is known about the actual roles of MCs during acute attacks of gout. This study was undertaken to assess the role of MCs in a mouse model of MSU crystal-induced acute arthritis.

METHODS

We assessed the effects of intraarticular (IA) injection of MSU crystals in various strains of mice with constitutive or inducible MC deficiency or in mice lacking interleukin-1β (IL-1β) or other elements of innate immunity. We also assessed the response to IA injection of MSU crystals in genetically MC-deficient mice after IA engraftment of wild-type or IL-1β(-/-) bone marrow-derived cultured MCs.

RESULTS

MCs were found to augment acute tissue swelling following IA injection of MSU crystals in mice. IL-1β production by MCs contributed importantly to MSU crystal-induced tissue swelling, particularly during its early stages. Selective depletion of synovial MCs was able to diminish MSU crystal-induced acute inflammation in the joints.

CONCLUSION

Our findings identify a previously unrecognized role of MCs and MC-derived IL-1β in the early stages of MSU crystal-induced acute arthritis in mice.

T lymphocytes maintain structure and function of fibroblastic reticular cells via lymphotoxin (LT)-B

Background

Although a lot is known about how Fibroblastic Reticular Cells (FRCs) can regulate T lymphocytes (T cells), little is understood about whether or how T cells can regulate FRCs.

Results

This study shows that the absence of T cells inhibited the secretion of ER-TR7 by splenic FRCs, induced the structural disorder of FRCs, down-regulated the expression of the chemokine ligands CCL21 and CCL19, and weakened the homing ability of T cells to the spleen of nude mice. Transfusion of T cells from BALB/c mice restored the structure and functions of FRCs and recovered them. The expression of lymphotoxin (LT)-B was significantly downregulated in the absence of T cells from nude mice and was recovered after the transfusion of T cells. After the occlusion of the LT-B receptor, the FRCs’ structure and functions were not restored by transfusion of T cells.

Conclusions

These data reveal that the absence of T cells will subject spleen FRCs to structural and functional abnormality, and weaken the homing ability of T cells to the spleen. These changes are attributed to the T-cell- derived LT-B.

Immune regulation during chronic visceral leishmaniasis

Visceral leishmaniasis is a chronic parasitic disease associated with severe immune dysfunction. Treatment options are limited to relatively toxic drugs, and there is no vaccine for humans available. Hence, there is an urgent need to better understand immune responses following infection with Leishmania species by studying animal models of disease and clinical samples from patients. Here, we review recent discoveries in these areas and highlight shortcomings in our knowledge that need to be addressed if better treatment options are to be developed and effective vaccines designed.

Myeloid suppressor cells require membrane TNFR2 expression for suppressive activity

TNF and TNF receptor type 2 (TNFR2) have been shown to be important for generation of myeloid-derived suppressor cells (MDSC). In order to analyze whether and how TNFR2 passes the effect of TNF on, myeloid cells from TNFR2-deficient mice were compared to respective cells from wild-type mice. Primary TNFR2-deficient myeloid cells showed reduced production of NO and IL-6 which was attributable to CD11b⁺ CD11c⁻ Ly6C⁺ Ly6G⁻ immature monocytic MDSC. TNFR2-deficient MDSC isolated from bone marrow were less suppressive for T cell proliferation compared to WT-derived MDSC. These differences on myeloid cells between the two mouse lines were still observed after co-culture of bone marrow cells from the two mouse lines together during myeloid cell differentiation, which demonstrated that the impaired functional capacity of TNFR2-deficient cells was independent of soluble factors but required membrane expression of TNFR2. Similarly, adoptive transfer of TNFR2-deficient bone marrow cells into wild-type hosts did not rescue the TNFR2-specific phenotype of bone marrow-derived myeloid cells. Therefore, membrane TNFR2 expression determines generation and function of monocytic MDSC.

RIPK1 regulates RIPK3-MLKL-driven systemic inflammation and emergency hematopoiesis

Upon ligand binding, RIPK1 is recruited to tumor necrosis factor receptor superfamily (TNFRSF) and Toll-like receptor (TLR) complexes promoting prosurvival and inflammatory signaling. RIPK1 also directly regulates caspase-8-mediated apoptosis or, if caspase-8 activity is blocked, RIPK3-MLKL-dependent necroptosis. We show that C57BL/6 Ripk1(-/-) mice die at birth of systemic inflammation that was not transferable by the hematopoietic compartment. However, Ripk1(-/-) progenitors failed to engraft lethally irradiated hosts properly. Blocking TNF reversed this defect in emergency hematopoiesis but, surprisingly, Tnfr1 deficiency did not prevent inflammation in Ripk1(-/-) neonates. Deletion of Ripk3 or Mlkl, but not Casp8, prevented extracellular release of the necroptotic DAMP, IL-33, and reduced Myd88-dependent inflammation. Reduced inflammation in the Ripk1(-/-)Ripk3(-/-), Ripk1(-/-)Mlkl(-/-), and Ripk1(-/-)Myd88(-/-) mice prevented neonatal lethality, but only Ripk1(-/-)Ripk3(-/-)Casp8(-/-) mice survived past weaning. These results reveal a key function for RIPK1 in inhibiting necroptosis and, thereby, a role in limiting, not only promoting, inflammation.

Inhibitors of apoptosis proteins (IAPs) are required for effective T-cell expansion/survival during antiviral immunity in mice

IAPs are required for survival and expansion of activated T cells. IAP antagonists sensitize to tumor necrosis factor (TNF)-induced cell death of activated T cells during viral infection.

TNF-α and its receptors modulate complex behaviours and neurotrophins in transgenic mice

Tumour necrosis factor-α (TNF-α) plays an important role not only in immunity but also in the normal functioning of the central nervous system (CNS). At physiological levels, studies have shown TNF-α is essential to maintain synaptic scaling and thus influence learning and memory formation while also playing a role in modulating pathological states of anxiety and depression. TNF-α signals mainly through its two receptors, TNF-R1 and TNF-R2, however the exact role that these receptors play in TNF-α mediated behavioural phenotypes is yet to be determined.

METHODS

We have assessed TNF(-/-), TNF-R1(-/-) and TNF-R2(-/-) mice against C57BL/6 wild-type (WT) mice from 12 weeks of age in order to evaluate measures of spatial memory and learning in the Barnes maze (BM) and Y-maze, as well as other behaviours such as exploration, social interaction, anxiety and depression-like behaviour in a battery of tests. We have also measured hippocampal and prefrontal cortex levels of the neurotrophins nerve growth factor (NGF) and brain derived neurotrophic factor (BDNF) as well as used immunohistochemical analyses to measure number of proliferating cells (Ki67) and immature neurons (DCX) within the dentate gyrus.

RESULTS

We have shown that young adult TNF(-/-) and TNF-R1(-/-) mice displayed impairments in learning and memory in the BM and Y-maze, while TNF-R2(-/-) mice showed good memory but slow learning in these tests. TNF(-/-)and TNF-R2(-/-) mice also demonstrated a decrease in anxiety like behaviour compared to WT mice. ELISA analyses showed TNF(-/-) and TNF-R2(-/-) mice had lower levels of NGF compared to WT mice.

CONCLUSION

These results indicate that while lack of TNF-α can decrease anxiety-like behaviour in mice, certain basal levels of TNF-α are required for the development of normal cognition. Furthermore our results suggest that both TNF-R1 and TNF-R2 signalling play a role in normal CNS function, with knockout of either receptor impairing cognition on the Barnes maze.

Dynamic changes in chromatin conformation at the TNF transcription start site in T helper lymphocyte subsets

Tumor necrosis factor (TNF) is one of the key primary response genes in the immune system that can be activated by a variety of stimuli. Previous analysis of chromatin accessibility to DNaseI demonstrated open chromatin conformation of the TNF proximal promoter in T cells. Here, using chromatin probing with restriction enzyme EcoNI and micrococcal nuclease we show that in contrast to the proximal promoter, the TNF transcription start site remains in a closed chromatin configuration in primary T helper (Th) cells, but acquires an open state after activation or polarization under Th1 and Th17 conditions. We further demonstrate that transcription factor c-Jun plays a pivotal role in the maintenance of open chromatin conformation at the transcription start site of the TNF gene.

Lymphotoxin α induces apoptosis, necroptosis and inflammatory signals with the same potency as tumour necrosis factor

Both of the TNF superfamily ligands, TNF and LTα, can bind and signal through TNFR1 and TNFR2, yet mice mutant for each have different phenotypes. Part of this difference is because LTα but not TNF can activate Herpes Virus Entry Mediator and also heterotrimerise with LTβ to activate LTβR, which is consistent with the similar phenotypes of the LTα and LTβR deficient mice. However, it has also been reported that the LTα3 homotrimer signals differently than TNF through TNFR1, and has unique roles in initiation and exacerbation of some inflammatory diseases. Our modeling of the TNF/TNFR1 interface compared to the LTα3/TNFR1 structure revealed some differences that could affect signalling by the two ligands. To determine whether there were any functional differences in the ability of TNF and LTα3 to induce TNFR1-dependent apoptosis or necroptosis, and if there were different requirements for cIAPs and Sharpin to transmit the TNFR1 signal, we compared the ability of cells to respond to TNF and LTα3. Contrary to our hypothesis, we were unable to discover differences in signalling by TNFR1 in response to TNF and LTα3. Our results imply that the reasons for the conservation of LTα are most likely due either to differential regulation, the ability to signal through Herpes Virus Entry Mediator or the ability of LTα to form heterotrimers with LTβ.

TNFα reverse signaling promotes sympathetic axon growth and target innervation

Reverse signaling via members of the tumor necrosis factor (TNF) superfamily controls multiple aspects of immune function. Here we document TNFα reverse signaling in the nervous system to our knowledge for the first time and show that it has a crucial role in establishing sympathetic innervation. During postnatal development, sympathetic axons express TNFα as they grow and branch in their target tissues, which in turn express TNF receptor 1 (TNFR1). In culture, soluble forms of TNFR1 act directly on postnatal sympathetic axons to promote growth and branching by a mechanism that depends on membrane-integrated TNFα and on downstream activation of ERK. Sympathetic innervation density is substantially lower in several tissues in postnatal and adult mice lacking either TNFα or TNFR1. These findings reveal that target-derived TNFR1 acts as a reverse-signaling ligand for membrane-integrated TNFα to promote growth and branching of sympathetic axons.

Loss of function of the mouse Sharpin gene results in Peyer's patch regression

Peyer’s patches (PP) are an important component in the immune response against intestinal pathogens. Two independent, spontaneous mutations in the mouse Sharpin gene (Sharpin^cpdm and Sharpin^cpdm-Dem) result in the absence of PP and disrupted splenic white pulp in adult mice, although a full complement of lymph nodes is present. Here we report that rudimentary PP begin to develop in Sharpin^cpdm mice during embryogenesis, but lack the organizational patterns that are typical of this tissue. In the present study, small intestines examined at weekly intervals from birth to maturity showed spontaneous regression of PP in mutant mice with concurrent infiltration of granulocytes. At 5 to 6 weeks of age, only indistinct remnants of granulocytic accumulations remain. Transplantation of normal bone marrow into Sharpin^cpdm mice at 7 days of age did not prevent regression of PP in bone marrow chimeras examined at 7 to 8 weeks of age. These findings indicate that SHARPIN expression is required for the normal development and maintenance, but not initiation, of PP.

The chymase mouse mast cell protease 4 degrades TNF, limits inflammation, and promotes survival in a model of sepsis

Mouse mast cell protease 4 (mMCP-4), the mouse counterpart of human mast cell chymase, is thought to have proinflammatory effects in innate or adaptive immune responses associated with mast cell activation. However, human chymase can degrade the proinflammatory cytokine TNF, a mediator that can be produced by mast cells and many other cell types. We found that mMCP-4 can reduce levels of mouse mast cell-derived TNF in vitro through degradation of transmembrane and soluble TNF. We assessed the effects of interactions between mMCP-4 and TNF in vivo by analyzing the features of a classic model of polymicrobial sepsis, cecal ligation and puncture (CLP), in C57BL/6J-mMCP-4-deficient mice versus C57BL/6J wild-type mice, and in C57BL/6J-Kit(W-sh/W-sh) mice containing adoptively transferred mast cells that were either wild type or lacked mMCP-4, TNF, or both mediators. The mMCP-4-deficient mice exhibited increased levels of intraperitoneal TNF, higher numbers of peritoneal neutrophils, and increased acute kidney injury after CLP, and also had significantly higher mortality after this procedure. Our findings support the conclusion that mMCP-4 can enhance survival after CLP at least in part by limiting detrimental effects of TNF, and suggest that mast cell chymase may represent an important negative regulator of TNF in vivo.

Concordance of preclinical and clinical pharmacology and toxicology of monoclonal antibodies and fusion proteins: soluble targets

Monoclonal antibodies (mAbs) and fusion proteins directed towards soluble targets make an important contribution to the treatment of disease. The purpose of this review was to correlate the clinical and preclinical data on the 14 currently approved mAbs and fusion proteins targeted to soluble targets. The principal sources used to gather data were: the peer reviewed Literature; European Medicines Agency 'Scientific Discussions' and United States Food and Drug Administration 'Pharmacology/Toxicology Reviews' and package inserts (United States Prescribing Information). Data on the following approved biopharmaceuticals were included: adalimumab, anakinra, bevacizumab, canakinumab, certolizumab pegol, denosumab, eculizumab, etanercept, golimumab, infliximab, omalizumab, ranibizumab, rilonacept and ustekinumab. Some related biopharmaceuticals in late-stage development were also included for comparison. Good concordance with human pharmacodynamics was found for both non-human primates (NHPs) receiving the human biopharmaceutical and mice receiving rodent homologues (surrogates). In contrast, there was limited concordance for human adverse effects in genetically deficient mice, mice receiving surrogates or NHPs receiving the human pharmaceutical. In summary, the results of this survey show that although both mice and NHPs have good predictive value for human pharmacodynamics, neither species have good predictive value for human adverse effects. No evidence that NHPs have superior predictive value was found.

Epithelial cell-derived IL-25, but not Th17 cell-derived IL-17 or IL-17F, is crucial for murine asthma

IL-17A, IL-17F, and IL-25 are ligands for IL-17RA. In the current study, we demonstrated that IL-25-deficient mice-but not IL-17A-, IL-17F-, IL-17A/F-, IL-23p19-, or retinoic acid-related orphan receptor (ROR)-γt-deficient mice-showed significant suppression of 1) the number of eosinophils and the levels of proinflammatory mediators in bronchoalveolar lavage fluids, 2) airway hyperresponsiveness to methacholine, and 3) OVA-specific IgG1 and IgE levels in the serum during OVA-induced Th2-type/eosinophilic airway inflammation. The IL-25 deficiency did not affect lung dendritic cell migration or Ag-specific memory-Th2 cell expansion during Ag sensitization. Adoptive transfer of T cells, mast cells, or bone marrow cells from IL-25-deficient mice revealed that induction of Th2-type/eosinophilic airway inflammation was dependent on activation of lung epithelial cells and eosinophils by IL-25 produced by airway structural cells such as epithelial cells but not by such hematopoietic stem-cell-origin immune cells as T cells and mast cells. Therefore, airway structural cell-derived IL-25-rather than Th17 cell-derived IL-17A and IL-17F-is responsible for induction of local inflammation by promoting activation of lung epithelial cells and eosinophils in the elicitation phase of Th2-type/eosinophilic airway inflammation. It is not required for Ag-specific Th2 cell differentiation in the sensitization phase.

B-lymphopoiesis is stopped by mobilizing doses of G-CSF and is rescued by overexpression of the anti-apoptotic protein Bcl2

Osteoblasts are necessary to B lymphopoiesis and mobilizing doses of G-CSF or cyclophosphamide inhibit osteoblasts, whereas AMD3100/Plerixafor does not. However, the effect of these mobilizing agents on B lymphopoiesis has not been reported. Mice (wild-type, knocked-out for TNF-α and TRAIL, or over-expressing Bcl-2) were mobilized with G-CSF, cyclophosphamide, or AMD3100. Bone marrow, blood, spleen and lymph node content in B cells was measured. G-CSF stopped medullar B lymphopoiesis with concomitant loss of B-cell colony-forming units, pre-pro-B, pro-B, pre-B and mature B cells and increased B-cell apoptosis by an indirect mechanism. Overexpression of the anti-apoptotic protein Bcl2 in transgenic mice rescued B-cell colony forming units and pre-pro-B cells in the marrow, and prevented loss of all B cells in marrow, blood and spleen. Blockade of endogenous soluble TNF-α with Etanercept, or combined deletion of the TNF-α and TRAIL genes did not prevent B lymphopoiesis arrest in response to G-CSF. Unlike G-CSF, treatments with cyclophosphamide or AMD3100 did not suppress B lymphopoiesis but caused instead robust B-cell mobilization. G-CSF, cyclophosphamide and AMD3100 have distinct effects on B lymphopoiesis and B-cell mobilization with: 1) G-CSF inhibiting medullar B lymphopoiesis without mobilizing B cells in a mechanism distinct from the TNF-α-mediated loss of B lymphopoiesis observed during inflammation or viral infections; 2) CYP mobilizing B cells but blocking their maturation; and 3) AMD3100 mobilizing B cells without affecting B lymphopoiesis. These results suggest that blood mobilized with these three agents may have distinct immune properties.

p100 Deficiency is insufficient for full activation of the alternative NF-κB pathway: TNF cooperates with p52-RelB in target gene transcription

Background

Constitutive activation of the alternative NF-κB pathway leads to marginal zone B cell expansion and disorganized spleen microarchitecture. Furthermore, uncontrolled alternative NF-κB signaling may result in the development and progression of cancer. Here, we focused on the question how does the constitutive alternative NF-κB signaling exert its effects in these malignant processes.

Methodology/Principal Findings

To explore the consequences of unrestricted alternative NF-κB activation on genome-wide transcription, we compared gene expression profiles of wild-type and NF-κB2/p100-deficient (p100^−/−) primary mouse embryonic fibroblasts (MEFs) and spleens. Microarray experiments revealed only 73 differentially regulated genes in p100^−/− vs. wild-type MEFs. Chromatin immunoprecipitation (ChIP) assays showed in p100^−/− MEFs direct binding of p52 and RelB to the promoter of the Enpp2 gene encoding ENPP2/Autotaxin, a protein with an important role in lymphocyte homing and cell migration. Gene ontology analysis revealed upregulation of genes with anti-apoptotic/proliferative activity (Enpp2/Atx, Serpina3g, Traf1, Rrad), chemotactic/locomotory activity (Enpp2/Atx, Ccl8), and lymphocyte homing activity (Enpp2/Atx, Cd34). Most importantly, biochemical and gene expression analyses of MEFs and spleen, respectively, indicated a marked crosstalk between classical and alternative NF-κB pathways.

Conclusions/Significance

Our results show that p100 deficiency alone was insufficient for full induction of genes regulated by the alternative NF-κB pathway. Moreover, alternative NF-κB signaling strongly synergized both in vitro and in vivo with classical NF-κB activation, thereby extending the number of genes under the control of the p100 inhibitor of the alternative NF-κB signaling pathway.

Hypoferraemia during the early inflammatory response is dependent on tumour necrosis factor activity in a murine model of protracted peritonitis

On the grounds of clinical, in vitro and in vivo studies, tumour necrosis factor (TNF) is considered to be one of the inflammatory cytokines that contributes to to the generation of hypoferraemia and anaemia of inflammation (AI). We used a recently described murine model for AI and hypoferraemia, based on sublethal caecal ligation and puncture (CLP) with ensuing protracted peritonitis, to investigate the contribution of TNF to the generation of hypoferraemia. During the early inflammatory response to CLP, a marked decrease in serum iron concentration occurs within 8 h. To determine whether TNF contributes to the generation of hypoferraemia at this time point, we studied TNF-deficient mice and wild-type mice that underwent CLP. The serum iron concentration was decreased in wild-type mice whereas TNF-deficient mice maintained normal serum iron levels following CLP. Hypoferraemia in wild-type mice was accompanied by the downregulation of ferroportin 1 (Fp1) in macrophages. In the macrophages of TNF-deficient mice, Fp1 was not downregulated following CLP. The initial expression of hepcidin was detectable at the mRNA level but not at the protein level by immunohisto-chemistry in wild-type and TNF-deficient mice. Therefore, hepcidin does not appear to be involved in the regulation of early hypoferraemia. TNF appears to regulate the expression of Fp1 by transcriptional control. Our results demonstrate that TNF mediates hypoferraemia during the early inflammatory response by regulating the expression of Fp1 in macrophages.

Autoreactive preplasma cells break tolerance in the absence of regulation by dendritic cells and macrophages

The ability to induce Ab responses to pathogens while maintaining the quiescence of autoreactive cells is an important aspect of immune tolerance. During activation of TLR4, dendritic cells (DCs) and macrophages (MFs) repress autoantibody production through their secretion of IL-6 and soluble CD40L (sCD40L). These soluble mediators selectively repress B cells chronically exposed to Ag, but not naive cells, suggesting a means to maintain tolerance during TLR4 stimulation, yet allow immunity. In this study, we identify TNF-α as a third repressive factor, which together with IL-6 and CD40L account for nearly all the repression conferred by DCs and MFs. Similar to IL-6 and sCD40L, TNF-α did not alter B cell proliferation or survival. Instead, it reduced the number of Ab-secreting cells. To address whether the soluble mediators secreted by DCs and MFs functioned in vivo, we generated mice lacking IL-6, CD40L, and TNF-α. Compared to wild-type mice, these mice showed prolonged anti-nuclear Ab responses following TLR4 stimulation. Furthermore, adoptive transfer of autoreactive B cells into chimeric IL-6(-/-) × CD40L(-/-) × TNF-α(-/-) mice showed that preplasma cells secreted autoantibodies independent of germinal center formation or extrafollicular foci. These data indicate that in the absence of genetic predisposition to autoimmunity, loss of endogenous IL-6, CD40L, and TNF-α promotes autoantibody secretion during TLR4 stimulation.

Loss of TNF signaling facilitates the development of a novel Ly-6C(low) macrophage population permissive for Leishmania major infection

In the absence of TNF, the normally resistant C57BL/6 (B6.WT) strain develops a fatal, progressive form of leishmaniasis after infection with Leishmania major. It is not yet understood which TNF activity or the lack thereof is responsible for the dramatic progression of leishmaniasis in TNF-negative (B6.TNF(-/-)) mice. To elucidate the underlying mechanisms resulting in the fatal outcome of L. major infection in this gene-deficient mouse strain, we analyzed the monocytic component of the inflammatory infiltrate in the draining popliteal lymph node and the site of the infection using multicolor flow cytometry. The leukocytic infiltrate within the draining lymph node and footpad of B6.TNF(-/-) mice resembled that of B6.WT mice over the first 2 wk of cutaneous L. major infection. Thereafter, the B6.TNF(-/-) mice showed an increase of CD11c(+)Ly-6C(+)CCR2(+) monocytic dendritic cells within the popliteal lymph node in comparison with B6.WT mice. This increase of inflammatory dendritic cells was paired with the accumulation of a novel CD11b(+)Ly-6C(low)CCR2(low) population that was not present in B6.WT mice. This B6.TNF(-/-)- and B6.TNFR1(-/-)-specific cell population was CD115(+)Ly-6G(-)iNOS(-), not apoptotic, and harbored large numbers of parasites.

The role of TRADD in death receptor signaling

TRADD (TNFR1-associated death domain protein) was initially identified as an adaptor molecule that transduces the signal downstream of the TNFR1 (tumor necrosis factor receptor 1). TNFR1 belongs to the so-called death receptor (DR) family of receptors that depending on the context can induce either apoptosis or proliferation, as well as NF-κB and MAP kinase activation. The receptors of this group contain death domain (DD) that is necessary for the induction of apoptosis. This review summarizes the recent advances in the field of DR signaling and in particular the role of TRADD.

Dendritic cells control lymphocyte entry to lymph nodes through high endothelial venules

While patrolling the body in search of foreign antigens, naive lymphocytes continuously circulate from the blood, through the lymph nodes, into the lymphatic vessels and back to the blood. This process, called lymphocyte recirculation, provides the body with effective immune surveillance for foreign invaders and for alterations to the body's own cells. However, the mechanisms that regulate lymphocyte recirculation during homeostasis remain incompletely characterized. Here we show that dendritic cells (DCs), which are well known for their role in antigen presentation to T lymphocytes, control the entry of naive lymphocytes to lymph nodes by modulating the phenotype of high endothelial venules (HEVs), which are blood vessels specialized in lymphocyte recruitment. We found that in vivo depletion of CD11c(+) DCs in adult mice over a 1-week period induces a reduction in the size and cellularity of the peripheral and mucosal lymph nodes. In the absence of DCs, the mature adult HEV phenotype reverts to an immature neonatal phenotype, and HEV-mediated lymphocyte recruitment to lymph nodes is inhibited. Co-culture experiments showed that the effect of DCs on HEV endothelial cells is direct and requires lymphotoxin-β-receptor-dependent signalling. DCs express lymphotoxin, and DC-derived lymphotoxin is important for lymphocyte homing to lymph nodes in vivo. Together, our results reveal a previously unsuspected role for DCs in the regulation of lymphocyte recirculation during immune surveillance.

Critical roles for LIGHT and its receptors in generating T cell-mediated immunity during Leishmania donovani infection

LIGHT (TNFSF14) is a member of the TNF superfamily involved in inflammation and defence against infection. LIGHT signals via two cell-bound receptors; herpes virus entry mediator (HVEM) and lymphotoxin-beta receptor (LTβR). We found that LIGHT is critical for control of hepatic parasite growth in mice with visceral leishmaniasis (VL) caused by infection with the protozoan parasite Leishmania donovani. LIGHT-HVEM signalling is essential for early dendritic cell IL-12/IL-23p40 production, and the generation of IFNγ- and TNF-producing T cells that control hepatic infection. However, we also discovered that LIGHT-LTβR interactions suppress anti-parasitic immunity in the liver in the first 7 days of infection by mechanisms that restrict both CD4⁺ T cell function and TNF-dependent microbicidal mechanisms. Thus, we have identified distinct roles for LIGHT in infection, and show that manipulation of interactions between LIGHT and its receptors may be used for therapeutic advantage.

Visceral leishmaniasis (VL) is a potentially fatal human disease caused by the intracellular protozoan parasites Leishmania donovani and L. infantum (chagasi). Parasites infect macrophages throughout the viscera, though the spleen and liver are the major sites of disease. VL is responsible for significant morbidity and mortality in the developing world, particularly in India, Sudan, Nepal, Bangladesh and Brazil. Because of the intrusive techniques required to analyse tissue in VL patients, our current understanding of the host immune response during VL largely derives from studies performed in genetically susceptible mice. We have discovered that mice which are unable to produce a cytokine called LIGHT have poor control of L. donovani infection in the liver, compared with wild-type control animals. In addition, we demonstrated that LIGHT has distinct roles during VL, depending on which of its two major cell-bound receptors it engages. Finally, we identified an antibody that stimulates the lymphotoxin β receptor (one of the LIGHT receptors), that can stimulate anti-parasitic activity during an established infection, thereby identifying this receptor as a therapeutic target during disease.

Requirement of interaction between mast cells and skin dendritic cells to establish contact hypersensitivity

The role of mast cells (MCs) in contact hypersensitivity (CHS) remains controversial. This is due in part to the use of the MC-deficient Kit ^W/Wv mouse model, since Kit ^W/Wv mice congenitally lack other types of cells as a result of a point mutation in c-kit. A recent study indicated that the intronic enhancer (IE) for Il4 gene transcription is essential for MCs but not in other cell types. The aim of this study is to re-evaluate the roles of MCs in CHS using mice in which MCs can be conditionally and specifically depleted. Transgenic Mas-TRECK mice in which MCs are depleted conditionally were newly generated using cell-type specific gene regulation by IE. Using this mouse, CHS and FITC-induced cutaneous DC migration were analyzed. Chemotaxis assay and cytoplasmic Ca²⁺ imaging were performed by co-culture of bone marrow-derived MCs (BMMCs) and bone marrow-derived dendritic cells (BMDCs). In Mas-TRECK mice, CHS was attenuated when MCs were depleted during the sensitization phase. In addition, both maturation and migration of skin DCs were abrogated by MC depletion. Consistently, BMMCs enhanced maturation and chemotaxis of BMDC in ICAM-1 and TNF-α dependent manners Furthermore, stimulated BMDCs increased intracellular Ca²⁺ of MC upon direct interaction and up-regulated membrane-bound TNF-α on BMMCs. These results suggest that MCs enhance DC functions by interacting with DCs in the skin to establish the sensitization phase of CHS.

Redundancy of interleukin-6 in the differentiation of T cell and monocyte subsets during cutaneous leishmaniasis

Leishmania (L.) major is a protozoan parasite that infects mammalian hosts and causes a spectrum of disease manifestations that is strongly associated with the genetic background of the host. Interleukin (IL)-6 is an acute phase proinflammatory cytokine, known in vitro to be involved in the inhibition of the generation of regulatory T cells. IL-6-deficient mice were infected with L. major, and T cell and monocyte subsets were analyzed with flow cytometry. Our data show that at the site of infection in the footpad and in the draining popliteal lymph node, numbers of regulatory T cells remain unchanged between WT and IL-6-deficient mice. However, the spleens of IL-6(-/-) mice contained fewer regulatory T cells after infection with L. major. The development of cutaneous lesions is similar between WT and IL-6-deficient mice, while parasite burden in IL-6(-/-) mice is reduced compared to WT. The development of IFN-γ or IL-10 producing T cells is similar in IL-6(-/-) mice. Despite a comparable adaptive T cell response, IL-6-deficient mice develop an earlier peak of some inflammatory cytokines than WT mice. This data indicate that the role of IL-6 in the differentiation of regulatory T cells is complex in vivo, and the effect of an absence of this cytokine can be counter-intuitive.

Heterogeneity of IL-22-producing Lymphoid Tissue Inducer-like Cells in Human and Mouse

Lymphoid tissue inducer (LTi) cells have been characterized in mouse as a key cell when secondary lymphoid tissues are organized during development and memory T cells are formed after birth. In addition to their involvement in adaptive immune responses, recent studies show that they contribute to innate immune responses by producing large amount of interleukin (IL)-22 against microbial attack. Here, we compare IL-22-producing LTi and LTi-like cells in human and mouse and discuss their heterogeneity in different tissues.

Immune-mediated mechanisms of parasite tissue sequestration during experimental cerebral malaria

Cerebral malaria is a severe complication of malaria. Sequestration of parasitized RBCs in brain microvasculature is associated with disease pathogenesis, but our understanding of this process is incomplete. In this study, we examined parasite tissue sequestration in an experimental model of cerebral malaria (ECM). We show that a rapid increase in parasite biomass is strongly associated with the induction of ECM, mediated by IFN-gamma and lymphotoxin alpha, whereas TNF and IL-10 limit this process. Crucially, we discovered that host CD4(+) and CD8(+) T cells promote parasite accumulation in vital organs, including the brain. Modulation of CD4(+) T cell responses by helminth coinfection amplified CD4(+) T cell-mediated parasite sequestration, whereas vaccination could generate CD4(+) T cells that reduced parasite biomass and prevented ECM. These findings provide novel insights into immune-mediated mechanisms of ECM pathogenesis and highlight the potential of T cells to both prevent and promote infectious diseases.

Mitogen-activated protein kinases p38 and ERK1/2 regulated control of Mycobacterium avium replication in primary murine macrophages is independent of tumor necrosis factor-α and interleukin-10

In macrophages, mitogen-activated protein kinases (MAPK) are critical regulators of both, mycobacterial replication and mycobacteria-induced cytokine formation. To segregate direct effects of MAPK function on mycobacterial replication from indirect, cytokine-mediated effects, we studied the growth of Mycobacterium avium strains in wild-type and tumor necrosis factor (TNF)-α- or interleukin (IL)-10-deficient bone marrow-derived murine macrophages. Using specific inhibitors of the p38- and the ERK1/2-MAPK pathways, we found that the use of SB203580 always reduced, whereas the presence of PD98059 always promoted, bacterial replication of highly virulent and intermediately virulent M. avium strains, independent of endogenous TNF-α or IL-10. The exogenous addition of TNF-α to TNF-α-deficient and wild-type M. avium-infected macrophages overrode the replication-reducing effect of SB203580, but not the replication-promoting effect of PD98059. In summary, our data demonstrate that a proper balance of MAPK activity is essential for macrophage control of M. avium growth, and that the ratio of the cytokines TNF-α and IL-10 can additionally modulate replication. Our findings indicate a novel therapeutic avenue for treating mycobacterial infections in particular by stimulating ERK1/2 or activating ERK1/2-dependent mechanisms in infected macrophages.

Cellular source and molecular form of TNF specify its distinct functions in organization of secondary lymphoid organs

Secondary lymphoid organs provide a unique microenvironment for generation of immune responses. Using a cell type-specific conditional knockout approach, we have dissected contributions of tumor necrosis factor (TNF) produced by B cells (B-TNF) or T cells (T-TNF) to the genesis and homeostatic organization of secondary lymphoid organs. In spleen, lymph nodes and Peyer patches, the cellular source of TNF, and its molecular form (soluble versus membrane-bound) appeared distinct. In spleen, in addition to major B-TNF signal, a complementary T-TNF signal contributed to the microstructure. In contrast, B-TNF predominantly controlled the development of follicular dendritic cells and B-cell follicles in Peyer patches. In lymph nodes, cooperation between TNF expressed by B and T cells was necessary for the maintenance of microarchitecture and for generation of an efficient humoral immune response. Unexpectedly, soluble but not membrane TNF expressed by B cells was essential for the organization of the secondary lymphoid organs. Thus, the maintenance of each type of secondary lymphoid organ is orchestrated by distinct contributions of membrane-bound and soluble TNF produced by B and T lymphocytes.

Blood-stage Plasmodium berghei infection leads to short-lived parasite-associated antigen presentation by dendritic cells

Despite extensive evidence that Plasmodium species are capable of stimulating the immune system, the association of malaria with a higher incidence of other infectious diseases and reduced responses to vaccination against unrelated pathogens suggests the existence of immune suppression. Recently, we provided evidence that blood-stage Plasmodium berghei infection leads to suppression of MHC class I-restricted immunity to third party (non-malarial) antigens as a consequence of systemic DC activation. This earlier study did not, however, determine whether reactivity was also impaired to MHC class II-restricted third party antigens or to Plasmodium antigens themselves. Here, we show that while P. berghei-expressed antigens were presented early in infection, there was a rapid decline in presentation within 4 days, paralleling impairment in MHC class I- and II-restricted presentation of third party antigens. This provides important evidence that P. berghei not only causes immunosuppression to subsequently encountered third party antigens, but also rapidly limits the capacity to generate effective parasite-specific immunity.

Tumor necrosis factor negative bone marrow-derived dendritic cells exhibit deficient IL-10 expression

The effective maturation of dendritic cells (DC) is complex and highly regulated and requires the presence of a variety of signals. Tumor necrosis factor (TNF) and its receptors or innate pattern recognition receptors such as the toll-like receptors have been shown to contribute to this process. DC derived from bone marrow cells in the presence of granulocyte/macrophage colony-stimulating factor can be used as a model to ascertain the contribution of different signals to DC maturation. Analysis of DC activated by addition of the mycobacterial vaccine strain Bacillus Calmette-Guérin showed that of the effector molecules studied only interleukin-10 expression was significantly reduced in TNF-negative (B6.TNF(-/-)) DC. Another effector molecule produced by DC, inducible nitric oxide synthase, was largely unchanged.

Estrogen receptor-beta activated apoptosis in benign hyperplasia and cancer of the prostate is androgen independent and TNFalpha mediated

Prostate cancer (PCa) and benign prostatic hyperplasia (BPH) are androgen-dependent diseases commonly treated by inhibiting androgen action. However, androgen ablation or castration fail to target androgen-independent cells implicated in disease etiology and recurrence. Mechanistically different to castration, this study shows beneficial proapoptotic actions of estrogen receptor-beta (ERbeta) in BPH and PCa. ERbeta agonist induces apoptosis in prostatic stromal, luminal and castrate-resistant basal epithelial cells of estrogen-deficient aromatase knock-out mice. This occurs via extrinsic (caspase-8) pathways, without reducing serum hormones, and perturbs the regenerative capacity of the epithelium. TNFalpha knock-out mice fail to respond to ERbeta agonist, demonstrating the requirement for TNFalpha signaling. In human tissues, ERbeta agonist induces apoptosis in stroma and epithelium of xenografted BPH specimens, including in the CD133(+) enriched putative stem/progenitor cells isolated from BPH-1 cells in vitro. In PCa, ERbeta causes apoptosis in Gleason Grade 7 xenografted tissues and androgen-independent cells lines (PC3 and DU145) via caspase-8. These data provide evidence of the beneficial effects of ERbeta agonist on epithelium and stroma of BPH, as well as androgen-independent tumor cells implicated in recurrent disease. Our data are indicative of the therapeutic potential of ERbeta agonist for treatment of PCa and/or BPH with or without androgen withdrawal.

Reduced nitro-oxidative stress and neural cell death suggests a protective role for microglial cells in TNFalpha-/- mice in ischemic retinopathy

PURPOSE

Neovascularization occurs in response to tissue ischemia and growth factor stimulation. In ischemic retinopathies, however, new vessels fail to restore the hypoxic tissue; instead, they infiltrate the transparent vitreous. In a model of oxygen-induced retinopathy (OIR), TNFalpha and iNOS, upregulated in response to tissue ischemia, are cytotoxic and inhibit vascular repair. The aim of this study was to investigate the mechanism for this effect.

METHODS

Wild-type C57/BL6 (WT) and TNFalpha(-/-) mice were subjected to OIR by exposure to 75% oxygen (postnatal days 7-12). The retinas were removed during the hypoxic phase of the model. Retinal cell death was determined by TUNEL staining, and the microglial cells were quantified after Z-series capture with a confocal microscope. In situ peroxynitrite and superoxide were measured by using the fluorescent dyes DCF and DHE. iNOS, nitrotyrosine, and arginase were analyzed by real-time PCR, Western blot analysis, and activity determined by radiolabeled arginine conversion. Astrocyte coverage was examined after GFAP immunostaining.

RESULTS

The TNFalpha(-/-) animals displayed a significant reduction in TUNEL-positive apoptotic cells in the inner nuclear layer of the avascular retina compared with that in the WT control mice. The reduction coincided with enhanced astrocytic survival and an increase in microglial cells actively engaged in phagocytosing apoptotic debris that displayed low ROS, RNS, and NO production and high arginase activity.

CONCLUSIONS

Collectively, the results suggest that improved vascular recovery in the absence of TNFalpha is associated with enhanced astrocyte survival and that both phenomena are dependent on preservation of microglial cells that display an anti-inflammatory phenotype during the early ischemic phase of OIR.

Soluble lymphotoxin is an important effector molecule in GVHD and GVL

Tumor necrosis factor (TNF) is a key cytokine in the effector phase of graft-versus-host disease (GVHD) after bone marrow transplantation, and TNF inhibitors have shown efficacy in clinical and experimental GVHD. TNF signals through the TNF receptors (TNFR), which also bind soluble lymphotoxin (LTα3), a TNF family member with a previously unexamined role in GVHD pathogenesis. We have used preclinical models to investigate the role of LT in GVHD. We confirm that grafts deficient in LTα have an attenuated capacity to induce GVHD equal to that seen when grafts lack TNF. This is not associated with other defects in cytokine production or T-cell function, suggesting that LTα3 exerts its pathogenic activity directly via TNFR signaling. We confirm that donor-derived LTα is required for graft-versus-leukemia (GVL) effects, with equal impairment in leukemic clearance seen in recipients of LTα- and TNF-deficient grafts. Further impairment in tumor clearance was seen using Tnf/Lta−/− donors, suggesting that these molecules play nonredundant roles in GVL. Importantly, donor TNF/LTα were only required for GVL where the recipient leukemia was susceptible to apoptosis via p55 TNFR signaling. These data suggest that antagonists neutralizing both TNF and LTα3 may be effective for treatment of GVHD, particularly if residual leukemia lacks the p55 TNFR.

Mast cell-derived TNF can exacerbate mortality during severe bacterial infections in C57BL/6-KitW-sh/W-sh mice

We used mast cell-engrafted genetically mast cell-deficient C57BL/6-Kit(W-sh/W-sh) mice to investigate the roles of mast cells and mast cell-derived tumor necrosis factor in two models of severe bacterial infection. In these mice, we confirmed findings derived from studies of mast cell-deficient WBB6F(1)-Kit(W/W-v) mice indicating that mast cells can promote survival in cecal ligation and puncture (CLP) of moderate severity. However, we found that the beneficial role of mast cells in this setting can occur independently of mast cell-derived tumor necrosis factor. By contrast, using mast cell-engrafted C57BL/6-Kit(W-sh/W-sh) mice, we found that mast cell-derived tumor necrosis factor can increase mortality during severe CLP and can also enhance bacterial growth and hasten death after intraperitoneal inoculation of Salmonella typhimurium. In WBB6F(1)-Kit(W-sh/W-sh) mice, mast cells enhanced survival during moderately severe CLP but did not significantly change the survival observed in severe CLP. Our findings in three types of genetically mast cell-deficient mice thus support the hypothesis that, depending on the circumstances (including mouse strain background, the nature of the mutation resulting in a mast cell deficiency, and type and severity of infection), mast cells can have either no detectable effect or opposite effects on survival during bacterial infections, eg, promoting survival during moderately severe CLP associated with low mortality but, in C57BL/6-Kit(W-sh/W-sh) mice, increasing mortality during severe CLP or infection with S. typhimurium.

The development of intestinal lymphoid tissues at the interface of self and microbiota

Intestinal lymphoid tissues face the challenging task of inducing adaptive immunity to pathogens, yet maintaining homeostasis with the enormous commensal microbiota. To that aim, the ancient partnership between self and flora has resulted in the generation of a unique set of lymphoid tissues capable of constant large-scale reformatting. A first set of lymphoid tissues, the mesenteric lymph nodes and Peyer's patches, are programmed to develop in the sterile environment of the fetus, whereas a second set of lymphoid tissues, the tertiary lymphoid tissues, are induced to form by the microbiota and inflammation. The diversity of intestinal lymphoid tissues confers the flexibility required to adapt the number of immune inductive sites to the size of the flora and the extent of the pathogenic threat. The result is a functional superorganism combining self and microbes for the best possible symbiosis.

Disparate role of LIGHT in organ-specific donor T cells activation and effector molecules in MHC class II disparate GVHD

BACKGROUND

The present studies determined the role of LIGHT on organ-specific cytokine and effector molecules in acute graft-versus-host disease.

METHODS

Cytokine and effector molecules were assessed by flow cytometry and quantitative PCR.

RESULTS

More CD4+ spleen cells (SpC) expressing interferon-gamma (IFNgamma) and interleukin-2 were noted in SpC isolated from lethally irradiated bm12 X B6 F1 recipients of B6 donor SpC and T cell-depleted bone marrow cells and control Adv-betagal than in transplant (bone marrow transplantation (BMT)) recipients who had received Adv-LTbetaR-Ig or Adv-herpes simplex virus entry mediator (HVEM)-Ig. IFNgamma RNA levels from SpC, small intestines, and large intestines of control BMT recipients were significantly higher than those who had received Adv-HVEM-Ig. Granzyme B levels from SpC and small intestines of control BMT recipients were significantly higher than those that had received the Adv-LTbetaR-Ig. In contrast, BMT recipients of Adv-HVEM-Ig had lower granzyme A levels than controls in their large intestines.

DISCUSSION

LIGHT inhibition differentially affects cytokines and effector molecules in SpC, small intestines, and large intestines, implicating different organ-specific pathways.

The effects of TNF deficiency on age-related cognitive performance

Growing evidence suggests that 'pro-inflammatory' cytokines such as TNF play a role in cognitive processes and in aging. To test the effects of TNF on cognitive function throughout aging, we used transgenic mice which were TNF deficient. We then tested these mice along with wild-type mice, at 3, 6 and 12 months of age, using the Barnes maze. Wild-type controls showed better memory than TNF knock-out mice at 3 months of age, but not at 6 and 12 months of age. Results of our experiment show that endogenous TNF plays an important role in cognitive processes throughout aging processes. The implications of these findings are far-reaching and include a possible role for cytokines in the molecular and cellular mechanisms subserving age-related changes in learning, memory and cognition.

Lymphotoxin-alpha and TNF have essential but independent roles in the evolution of the granulomatous response in experimental leprosy

Recent studies identified an association between genetic variants in the lymphotoxin-alpha (LTalpha) gene and leprosy. To study the influence of LTalpha on the control of experimental leprosy, both low- and high-dose Mycobacterium leprae foot pad (FP) infections were evaluated in LTalpha-deficient chimeric (cLTalpha(-/-)) and control chimeric (cB6) mice. Cellular responses to low-dose infection in cLTalpha(-/-) mice were dramatically different, with reduced accumulation of CD4(+) and CD8(+) lymphocytes and macrophages and failure to form granulomas. Growth of M. leprae was contained for 6 months, but augmented late in infection. In contrast, tumor necrosis factor knockout and tumor necrosis factor receptor 1 knockout FPs exhibited extensive inflammatory infiltration with an increase in M. leprae growth throughout infection. Following high-dose infection, cB6 FP induration peaked at 4 weeks and was maintained for 12 weeks. Induration was not sustained in cLTalpha(-/-) FPs that contained few lymphocytes and no granulomas. There was a reduction in the expression levels of inflammatory cytokines, chemokines, and chemokine receptors, including nitric oxide synthase 2, vascular cell adhesion molecule, and intercellular cell adhesion molecule. Furthermore, cLTalpha(-/-) popliteal lymph nodes contained a higher proportion of naïve CD44(lo)CD62L(hi) T cells than cB6 mice, suggestive of reduced T cell activation. Therefore, both LTalpha and tumor necrosis factor are essential for the regulation of the granuloma, but they have distinctive roles in the recruitment of lymphocytes and maintenance of the granulomatous response during chronic M. leprae infection.

Rel/NF-kappaB family member RelA regulates NK1.1- to NK1.1+ transition as well as IL-15-induced expansion of NKT cells

Development of NKT cells was shown to depend on lymphotoxin (LT) and IL-15 signaling pathways as well as on cytokine receptor common gamma chain. After positive selection, NKT-cell precursors transit through progressive maturation stages including proliferative expansion within the NK1.1(-) window. The transcription factors that integrate different signaling pathways into different stages of NKT-cell development are not well characterized. Here, we show that the Rel/NF-kappaB family member RelA regulates the NK1.1(-) to NK1.1(+) transition during NKT-cell development. RelA is also required for both IL-15- and IL-7-induced proliferation of CD44(hi)NK1.1(-) NKT-cell precursors. Activation of the invariant NKT-cell receptor induces both IL-15 receptor alpha and gamma chains' expression in an NF-kappaB-dependent manner, suggesting a molecular mechanism by which NF-kappaB regulates NKT-cell development. NF-kappaB also regulates TCR-induced expression of LT-alpha and LT-beta within NKT cells. In contrast to previous reports, however, we show that LT signaling is dispensable for thymic NKT-cell development but is essential for their colonization of peripheral organs such as liver.

Fatal hepatitis mediated by tumor necrosis factor TNFalpha requires caspase-8 and involves the BH3-only proteins Bid and Bim

Apoptotic death of hepatocytes, a contributor to many chronic and acute liver diseases, can be a consequence of overactivation of the immune system and is often mediated by TNFalpha. Injection with lipopolysaccharide (LPS) plus the transcriptional inhibitor D(+)-galactosamine (GalN) or mitogenic T cell activation causes fatal hepatocyte apoptosis in mice, which is mediated by TNFalpha, but the effector mechanisms remain unclear. Our analysis of gene-targeted mice showed that caspase-8 is essential for hepatocyte killing in both settings. Loss of Bid, the proapoptotic BH3-only protein activated by caspase-8 and essential for Fas ligand-induced hepatocyte killing, resulted only in a minor reduction of liver damage. However, combined loss of Bid and another BH3-only protein, Bim, activated by c-Jun N-terminal kinase (JNK), protected mice from LPS+GalN-induced hepatitis. These observations identify caspase-8 and the BH3-only proteins Bid and Bim as potential therapeutic targets for treatment of inflammatory liver diseases.

Follicular dendritic cells and human immunodeficiency virus type 1 transcription in CD4+ T cells

HIV replication occurs throughout the natural course of infection in secondary lymphoid tissues and in particular within the germinal centers (GCs), where follicular dendritic cells (FDCs) are adjacent to CD4(+) T cells. Because FDCs provide signaling that increases lymphocyte activation, we postulated that FDCs could increase human immunodeficiency virus (HIV) replication. We cultured HIV-infected CD4(+) T cells alone or with FDCs and measured subsequent virus expression using HIV-p24 production and reverse transcription-PCR analyses. When cultured with FDCs, infected CD4(+) T cells produced almost fourfold more HIV than when cultured alone, and the rate of virus transcription was doubled. Both FDCs and their supernatant increased HIV transcription and resulted in nuclear translocation of NF-kappaB and phosphorylated c-Jun in infected cells. FDCs produced soluble tumor necrosis factor alpha (TNF-alpha) ex vivo, and the addition of a blocking soluble TNF receptor ablated FDC-mediated HIV transcription. Furthermore, TNF-alpha was found highly expressed within GCs, and ex vivo GC CD4(+) T cells supported greater levels of HIV-1 replication than other CD4(+) T cells. These data indicated that FDCs increase HIV transcription and production by a soluble TNF-alpha-mediated mechanism. This FDC-mediated effect may account, at least in part, for the presence of persistent HIV replication in GCs. Therefore, in addition to providing an important reservoir of infectious virus, FDCs increase HIV production, contributing to a tissue microenvironment that is highly conducive to HIV transmission and expression.

Cognitive dysfunction in mice deficient for TNF- and its receptors

Recent evidence suggests a role for tumor necrosis factor alpha (TNF) in the functioning of the central nervous system (CNS). The aim of this work was to examine the effect of a deficiency of TNF (TNF(-/-)) and its main receptors (TNF-R1(-/-) and TNF-R2(-/-)) on cognitive function. A standardized survey on cognition-like behavior assessing learning and retention, spatial learning/memory, cognitive flexibility, and learning effectiveness was used in B6.WT and B6.TNF gene targeted mice strains (B6.wild-type, B6.TNF(-/-), B6.TNF-R1(-/-), B6.TNF-R2(-/-) mice). All studied mice strains demonstrated successful exploration and learning processes during the training phases of the tests, which made the specific cognition-like tests valid in these mice strains. In the specific cognition-like tests, the B6.TNF(-/-) mice demonstrated significantly poorer learning and retention in the novel object test compared to B6.WT, B6.TNF-R1(-/-) and B6.TNF-R2(-/-) mice. In addition, spatial learning and learning effectiveness were significantly poorer in B6.TNF(-/-) mice compared to B6.WT mice. Moreover, the moderately impaired cognitive performance with similar degrees in B6.TNF-R1(-/-) or B6.TNF-R2(-/-) mice was generally better than in TNF(-/-) mice but also poorer than in B6.WT mice. While the absence of TNF was correlated with poor cognitive functioning, the deletion of both TNF-receptors was involved in partially reduced cognitive functioning. Low-levels of TNF under non-inflammatory immune conditions appear essential for normal cognitive function. TNF displays an interesting candidate gene for cognitive function. Translational research is required to investigate associations between genetic variants of TNF and cognitive function in healthy subjects and neuropsychiatric samples.

A subset of IL-10-producing gammadelta T cells protect the liver from Listeria-elicited, CD8(+) T cell-mediated injury

Although gammadelta T cells play a role in protecting tissues from pathogen-elicited damage to bacterial, viral and parasitic pathogens, the mechanisms involved in the damage and in the protection have not been clearly elucidated. This has been addressed using a murine model of listeriosis, which in mice lacking gammadelta T cells (TCRdelta(-/-)) is characterised by severe and extensive immune-mediated hepatic necrosis. We show that these hepatic lesions are caused by Listeria-elicited CD8(+) T cells secreting high levels of TNF-alpha that accumulate in the liver of Listeria-infected TCRdelta(-/-) mice. Using isolated populations of gammadelta T cells from wild-type and cytokine-deficient strains of mice to reconstitute TCRdelta(-/-) mice, the TCR variable gene 4 (Vgamma4)(+) subset of gammadelta T cells was shown to protect against liver injury. Hepatoprotection was dependent upon their ability to produce IL-10 after TCR-mediated interactions with Listeria-elicited macrophages and CD8(+) T cells. IL-10-producing Vgamma4(+) T cells also contribute to controlling CD8(+) T cell expansion and to regulating and reducing TNF-alpha secretion by activated CD8(+) T cells. This effect on TNF-alpha production was directly attributed to IL-10. These findings identify a novel mechanism by which pathogen-elicited CD8(+) T cells are regulated via interactions with, and activation of, IL-10-producing hepatoprotective gammadelta T cells.

Effects of Administration of a Monoclonal Antibody against Mouse Tumor Necrosis Factor Alpha during Pregnancy and Lactation on the Pre- and Postnatal Development of the Mouse Immune System

Monoclonal antibodies directed against tumor necrosis factor alpha (TNF α) are currently employed in the treatment of various immune-mediated diseases. These studies were designed to evaluate potential effects of anti-TNF αtreatment in mice during pregnancy and lactation on the development of the immune system in the F1 generation. Pregnant CD-1 mice were treated with vehicle or with 10 or 40 mg/kg of an anti-mouse TNF αmonoclonal antibody (mAb) (cV1q) on days 6, 12, and 18 of gestation and on days 3, 9, and 15 of lactation. Evaluation of immune system functionality was conducted in F1 generation mice at 11 weeks of age. Immune function was evaluated by splenocyte phenotyping, immunoglobulin M (IgM) antibody response to sheep red blood cells (SRBCs), spleen cell proliferative response to anti-CD3, and natural killer cell activity. Treatment of pregnant mice with cV1q produced no adverse effects in the dams and no adverse effects in the F1 generation. In general, the functioning of the immune system of the F1 generation did not appear to be adversely affected following exposure to cV1q in utero and during lactation. The only statistically significant change was a slight (~20%) reduction in the spleen cell expansion in response to SRBC immunization in the female F1 mice from the 40 mg/kg cV1q treatment group. In conclusion, administration of a monoclonal antibody against mouse TNF αduring pregnancy and lactation had little or no effect on selected immune parameters in mice, with only a possible minor attenuation of spleen cell response to immunization noted in the female F1 generation at 11 weeks of age.

Separation of splenic red and white pulp occurs before birth in a LTalphabeta-independent manner

For the formation of lymph nodes and Peyer's patches, lymphoid tissue inducer (LTi) cells are crucial in triggering stromal cells to recruit and retain hematopoietic cells. Although LTi cells have been observed in fetal spleen, not much is known about fetal spleen development and the role of LTi cells in this process. Here, we show that LTi cells collect in a periarteriolar manner in fetal spleen at the periphery of the white pulp anlagen. Expression of the homeostatic chemokines can be detected in stromal and endothelial cells, suggesting that LTi cells are attracted by these chemokines. As lymphotoxin (LT)alpha1beta2 can be detected on B cells but not LTi cells in neonatal spleen, starting at 4 days after birth, the earliest formation of the white pulp in fetal spleen occurs in a LTalpha1beta2-independent manner. The postnatal development of the splenic white pulp, involving the influx of T cells, depends on LTalpha1beta2 expressed by B cells.