Stimulation of TNF receptor type 2 expands regulatory T cells and ameliorates established collagen-induced arthritis in mice

Tumor necrosis factor (TNF) and its receptors TNF receptor type 1 (TNFR1) and type 2 (TNFR2) have a central role in chronic inflammatory diseases. While TNFR1 mainly confers inflammation, activation of TNFR2 elicits not only pro-inflammatory but also anti-inflammatory effects. In this study, we wanted to investigate the anti-inflammatory therapeutic potential of selective activation of TNFR2 in mice with established collagen-induced arthritis. Mice with established arthritis induced by immunization with bovine collagen type II were treated with six injections of the TNFR2-specific agonist TNCscTNF80, given every second day. Two days after treatment cessation, the cell compositions of bone marrow, spleen and lymph nodes were analyzed. Mice were visually scored until day 30 after the start of therapy and the degree of joint inflammation was determined by histology. Treatment with TNCscTNF80 increased arthritis-induced myelopoiesis. Little effect was seen on the infiltration rate of inflammatory immature myeloid cells and on the reduction of lymphoid cells in secondary lymphoid organs. Upon treatment, frequency of regulatory T (Treg) cells in the CD4⁺ T-cell population was increased in both spleen and inguinal lymph nodes. In addition, the expression of TNFR2 on Treg cells was enhanced. The clinical score started to improve 1 week after cessation treatment and remained lower 30 days after initiation of therapy. The histological score also revealed amelioration of joint inflammation in TNCscTNF80-treated versus control mice. Activation of TNFR2 might provide a suitable therapeutic strategy in autoimmune arthritis by increasing the numbers of regulatory cell types, in particular Treg cells, and by attenuation of arthritis.

Chronic Inflammation Increases the Sensitivity of Mouse Treg for TNFR2 Costimulation

TNF receptor type 2 (TNFR2) has gained attention as a costimulatory receptor for T cells and as critical factor for the development of regulatory T cells (Treg) and myeloid suppressor cells. Using the TNFR2-specific agonist TNCscTNF80, direct effects of TNFR2 activation on myeloid cells and T cells were investigated in mice. In vitro, TNCscTNF80 induced T cell proliferation in a costimulatory fashion, and also supported in vitro expansion of Treg cells. In addition, activation of TNFR2 retarded differentiation of bone marrow-derived immature myeloid cells in culture and reduced their suppressor function. In vivo application of TNCscTNF80-induced mild myelopoiesis in naïve mice without affecting the immune cell composition. Already a single application expanded Treg cells and improved suppression of CD4 T cells in mice with chronic inflammation. By contrast, multiple applications of the TNFR2 agonist were required to expand Treg cells in naïve mice. Improved suppression of T cell proliferation depended on expression of TNFR2 by T cells in mice repeatedly treated with TNCscTNF80, without a major contribution of TNFR2 on myeloid cells. Thus, TNFR2 activation on T cells in naïve mice can lead to immune suppression in vivo. These findings support the important role of TNFR2 for Treg cells in immune regulation.

Exogenous TNFR2 activation protects from acute GvHD via host T reg cell expansion

Activation of TNFR2 with a novel agonist expands T reg cells in vivo and protects allo-HCT recipients from acute GvHD while sparing antilymphoma and antiinfectious properties of transplanted donor T cells.

Donor CD4⁺Foxp3⁺ regulatory T cells (T reg cells) suppress graft-versus-host disease (GvHD) after allogeneic hematopoietic stem cell transplantation (HCT [allo-HCT]). Current clinical study protocols rely on the ex vivo expansion of donor T reg cells and their infusion in high numbers. In this study, we present a novel strategy for inhibiting GvHD that is based on the in vivo expansion of recipient T reg cells before allo-HCT, exploiting the crucial role of tumor necrosis factor receptor 2 (TNFR2) in T reg cell biology. Expanding radiation-resistant host T reg cells in recipient mice using a mouse TNFR2-selective agonist before allo-HCT significantly prolonged survival and reduced GvHD severity in a TNFR2- and T reg cell–dependent manner. The beneficial effects of transplanted T cells against leukemia cells and infectious pathogens remained unaffected. A corresponding human TNFR2-specific agonist expanded human T reg cells in vitro. These observations indicate the potential of our strategy to protect allo-HCT patients from acute GvHD by expanding T reg cells via selective TNFR2 activation in vivo.

Induction of Suppressor Cells and Increased Tumor Growth following Chronic Psychosocial Stress in Male Mice

To study the impact of psychosocial stress on the immune system, male mice were subjected to chronic subordinate colony housing (CSC), a preclinically validated mouse model for chronic psychosocial stress. CSC substantially affected the cell composition of the bone marrow, blood, and spleen by inducing myelopoiesis and enhancing the frequency of regulatory T cells in the CD4 population. Expansion of the myeloid cell compartment was due to cells identified as immature inflammatory myeloid cells having the phenotype of myeloid-derived suppressor cells of either the granulocytic or the monocytic type. Catecholaminergic as well as TNF signaling were implicated in these CSC-induced cellular shifts. Although the frequency of regulatory cells was enhanced following CSC, the high capacity for inflammatory cytokine secretion of total splenocytes indicated an inflammatory immune status in CSC mice. Furthermore, CSC enhanced the suppressive activity of bone marrow-derived myeloid-derived suppressor cells towards proliferating T cells. In line with the occurrence of suppressor cell types such as regulatory T cells and myeloid-derived suppressor cells, transplanted syngeneic fibrosarcoma cells grew better in CSC mice than in controls, a process accompanied by pronounced angiogenesis and clustering of immature myeloid cells in the tumor tissue. In addition, tumor implantation after CSC reinforced the CSC-induced increase in myeloid-derived suppressor cells and regulatory T cell frequencies while the CSC-induced cellular changes eased off in mice without tumor. Together, our data suggest a role for suppressor cells such as regulatory T cells and myeloid-derived suppressor cells in the enhanced tumor growth after chronic psychosocial stress.

TNF and regulatory T cells are critical for sepsis-induced suppression of T cells

The immune system in sepsis is impaired as seen by reduced numbers and function of immune cells and impaired antigen-specific antibody responses. We studied T cell function in septic mice using cecal ligation and puncture (CLP) as a clinically relevant mouse model for sepsis. The proliferative response of CD4(+) and CD8(+) T cells was suppressed in septic mice. Adoptive transfer experiments demonstrated that the T cells were not intrinsically altered by CLP. Instead, the septic host environment was responsible for this T cell suppression. While CLP-induced suppression was dependent on TNF activity, neither the activation of TNF receptors type 1 nor TNF receptor type 2 alone was sufficient to generate sepsis-induced suppression showing that the two TNF receptors can substitute each other. Specific depletion of regulatory T (Treg) cells improved the impaired T cell proliferation in septic recipients demonstrating participation of Treg in sepsis-induced suppression. In summary, sepsis leads to TNF-dependent suppression of T cell proliferation in vivo involving induction of Treg cells.

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.

Immune humanization of immunodeficient mice using diagnostic bone marrow aspirates from carcinoma patients

Tumor xenografts in immunodeficient mice, while routinely used in cancer research, preclude studying interactions of immune and cancer cells or, if humanized by allogeneic immune cells, are of limited use for tumor-immunological questions. Here, we explore a novel way to generate cancer models with an autologous humanized immune system. We demonstrate that hematopoietic stem and progenitor cells (HSPCs) from bone marrow aspirates of non-metastasized carcinoma patients, which are taken at specialized centers for diagnostic purposes, can be used to generate a human immune system in NOD-scid IL2rγ(null) (NSG) and HLA-I expressing NSG mice (NSG-HLA-A2/HHD) comprising both, lymphoid and myeloid cell lineages. Using NSG-HLA-A2/HHD mice, we show that responsive and self-tolerant human T cells develop and human antigen presenting cells can activate human T cells. As critical factors we identified the low potential of bone marrow HSPCs to engraft, generally low HSPC numbers in patient-derived bone marrow samples, cryopreservation and routes of cell administration. We provide here an optimized protocol that uses a minimum number of HSPCs, preselects high-quality bone marrow samples defined by the number of initially isolated leukocytes and intra-femoral or intra-venous injection. In conclusion, the use of diagnostic bone marrow aspirates from non-metastasized carcinoma patients for the immunological humanization of immunodeficient mice is feasible and opens the chance for individualized analyses of anti-tumoral T cell responses.

Immature mouse granulocytic myeloid cells are characterized by production of ficolin-B

Ficolins activate the lectin pathway of the complement system upon binding to carbohydrate patterns on pathogens. To characterize the producer cells of ficolin-B the expression of mouse ficolin-B, the orthologue of human M-ficolin, was studied in macrophages and dendritic cells during differentiation from bone marrow cells, in primary granulocytes, and during differentiation of granulocytes derived from ER-Hoxb8 cells. Expression of ficolin-B mRNA declined in all myeloid cell types to low levels during terminal differentiation. However, in contrast to macrophages and dendritic cells, ficolin-B expression was enhanced upon activation in granulocytes. High expression of ficolin-B was observed in primary immature neutrophilic CD11b(+) Ly-6C(int) Ly-6G(high) granulocytes when isolated from the bone marrow, in particular during sepsis. Ficolin-B was demonstrated in lysates of primary granulocytes, ER-Hoxb8-derived granulocytes, bone marrow-derived macrophages, and dendritic cells. Native ficolin-B from cell lysates and supernatants of granulocytes activated the lectin pathway as measured by binding to MASP-2 and inducing C4 deposition. Specific staining demonstrated intra-cellular or cell associated ficolin-B protein in activated immature granulocytes deposited in a granular fashion. This study shows that ficolin-B is stored in and set free from immature granulocytic myeloid cells indicating a role in the early infection-induced cellular response of these inflammatory cells.

TNFR2 maintains adequate IL-12 production by dendritic cells in inflammatory responses by regulating endogenous TNF levels

Sepsis-induced immune reactions are reduced in TNF receptor 2 (TNFR2)-deficient mice as previously shown. In order to elucidate the underlying mechanisms, the functional integrity of myeloid cells of TNFR2-deficient mice was analyzed and compared to wild type (WT) mice. The capacity of dendritic cells to produce IL-12 was strongly impaired in TNF-deficient mice, mirroring impaired production of IL-12 by WT dendritic cells in sepsis or after LPS or TNF pre-treatment. In addition, TNFR2-deficient mice were refractory to LPS pre-treatment and also to hyper-sensitization by inactivated Propionibacterium acnes, indicating habituation to inflammatory stimuli by the immune response when TNFR2 is lacking. Constitutive expression of TNF mRNA in kidney, liver, spleen, colon and lung tissue, and the presence of soluble TNFR2 in urine of healthy WT mice supported the conclusion that TNF is continuously present in naïve mice and controlled by soluble TNFR2. In TNFR2-deficient mice endogenous TNF levels cannot be balanced and the continuous exposure to enhanced TNF levels impairs dendritic cell function. In conclusion, TNF pre-exposure suppresses secondary inflammatory reactions of myeloid cells; therefore, continuous control of endogenous TNF by soluble TNFR2 seems to be essential for the maintenance of adequate sensitivity to inflammatory stimuli.

LTβR expression on hematopoietic cells regulates acute inflammation and influences maturation of myeloid subpopulations

Lymphotoxin beta-receptor (LTβR) is involved in the formation and maintenance of secondary lymphoid structures, as well as in the regulation of inflammatory responses. Because LTβR lymphoid structure formation continues to develop in infants, we compared two different chimera models: one using adult mice and the other using a transplantation model of neonatal mice. To elucidate the function of LTβR on lymphoid and non-lymphoid cells, we generated bone marrow chimeras on the wild type C57Bl/6 and the LTβR-deficient (LTβR(-/-)) background, and reconstituted the mice with bone marrow cells reciprocally. These chimeric mice were analyzed in the experimental model of acute dextran sulfate sodium-induced colitis. Interestingly, both models revealed not only equal reconstitution levels but also similar immunological responses: LTβR expression on stromal cells is essential for lymph node formation, whereas LTBR on hematopoietic cells is crucial for a decrease in inflammation. In addition, mice lacking LTβR on hematopoietic cells revealed (a) an increase of immature granulocytic cells in the spleen and (b) a reduced proportion of myeloid cells in peripheral blood and spleen expressing CD11b(+)Ly6C(+)Ly6G(-) (myeloid-derived suppressor cells expression profile). In conclusion, LTβR expression on hematopoietic cells seems to be involved in the down-regulation of acute inflammatory reactions paralleled by the appearance of immature myeloid cells.

Functional analysis of mouse ficolin-B and detection in neutrophils

Ficolins and mannan-binding lectin recognize pathogen-associated molecular patterns and initiate the lectin pathway of complement activation via the associated serine proteases. In contrast to human ficolins and mouse ficolin-A, mouse ficolin-B has been considered incapable of complement activation. Dose-dependent binding of recombinant ficolin-B to immobilized GlcNAc, acetylated BSA, acetylated LDL, and fetuin was detected with ficolin-B-specific monoclonal antibodies. Recombinant ficolin-B bound to immobilized acetylated bovine serum albumin interacted with recombinant human mannan-binding lectin-associated serine protease-2, which led to C4 cleavage, thus demonstrating the capability of ficolin-B to activate the lectin pathway. Ficolin-B-specific monoclonal antibodies identified natural ficolin-B protein in lysates of mouse granulocytes isolated from the bone marrow. These results identify mouse ficolin-B as a functional member of the ficolin family activating complement via the lectin pathway.

An early reduction in Treg cells correlates with enhanced local inflammation in cutaneous leishmaniasis in CCR6-deficient mice

Resistance to Leishmania major infection is dependent on the development of a cell-mediated Th1 immune response in resistant C57BL/6 mice whereas Th2-prone BALB/c mice develop non-healing lesions after infection. The chemokine receptor CCR6 is shared by anti-inflammatory regulatory T cells and pro-inflammatory Th17 cells. In a recent study we showed that C57BL/6 mice deficient in CCR6 exhibited enhanced footpad swelling and impaired T helper cell migration indicated by reduced recruitment of total T helper cells into the skin after infection and a reduced delayed type hypersensitivity reaction. Based on these findings we tested whether the lack of CCR6 alters Treg or Th17 cell responses during the course of Leishmania major infection. When we analyzed T cell subsets in the lymph nodes of CCR6-deficient mice, Th17 cell numbers were not different. However, reduced numbers of Treg cells paralleled with a stronger IFNγ response. Furthermore, the early increase in IFNγ-producing cells correlated with increased local tissue inflammation at later time points. Our data indicate an important role of CCR6 for Treg cells and a redundant role for Th17 cells in a Th1 cell-driven anti-parasitic immune response against Leishmania major parasites in resistant C57BL/6 mice.

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.

Ficolin-B marks apoptotic and necrotic cells

Ficolins are a group of proteins consisting of a fibrinogen-like and a collagen-like domain. They play a role in innate immunity by activating the complement system via the lectin pathway upon binding to carbohydrate patterns on pathogens. Two types of ficolins have been identified in mice, ficolin A and ficolin B (FcnB). We show in this article that recombinant FcnB binds to late apoptotic cells and to apoptotic bodies as well as to necrotic cells but not to early apoptotic cells. This binding was calcium-dependent and could be competitively inhibited by acetylated BSA, a classical binding substrate of FcnB. In addition, DNA inhibited binding of FcnB to apoptotic and necrotic cells, indicating that DNA exposed by dying cells could also be a ligand for FcnB. Thus, FcnB may play a role in the removal of damaged host cells and maintenance of tissue homeostasis.

Immune cell populations and cytokine production in spleen and mesenteric lymph nodes after laparoscopic surgery versus conventional laparotomy in mice

PURPOSE

There is evidence that open as well as minimally invasive abdominal surgery impair post-operative innate and acquired immune function. To compare the impact of these approaches as well as the one of different peritoneal gas exposures on immune function, we investigated cellular as well as cytokine-based immune parameters in mesenteric lymph nodes and the spleen postoperatively.

METHODS

Mice (n = 26) were randomly assigned to the 4 study groups: (1) sham controls undergoing anesthesia alone, (2) laparotomy, and (3) air, or (4) carbon dioxide pneumoperitoneum. Mice were sacrificed 48 h after the intervention, and their spleens and mesenteric lymph nodes were harvested. Cytokine production (TNF-α, IL-6, IL-10, and IFN-γ), splenic T cell subpopulations (cytotoxic T cells, T helper cells, and regulatory T cells) were analyzed.

RESULTS

TNF-α production of splenocytes 16 h after ex vivo lipopolysaccharides (LPS) stimulation was significantly increased in the laparotomy group compared to all other groups. In contrast, TNF-α production of lymph node cells and IL-6 production of splenocytes after ex vivo LPS stimulation did not differ significantly between the groups. The numbers of regulatory T cells (Treg) in the spleen differed between groups. A significant reduction in Treg cell frequency was detected in the CO(2) insufflation group compared to the laparotomy and the air insufflation group.

CONCLUSION

Our findings demonstrate a distinct difference in immune effector functions and cellular composition of the spleen with regard to splenic TNF-α production and increased numbers of Treg cells in the spleen. These findings are in line with a higher peritoneal inflammatory status consequent to peritoneal air rather than CO(2) exposure. Treg turned out to be key modulators of postoperative dysfunction of acquired immunity.

Sepsis leads to a reduced antigen-specific primary antibody response

Immunosuppression, impaired cytokine production and high susceptibility to secondary infections are characteristic for septic patients, and for mice after induction of polymicrobial septic peritonitis by sublethal cecal ligation and puncture (CLP). Here, we demonstrate that CLP markedly altered subsequent B-cell responses. Total IgG and IgM levels, as well as the memory B-cell response, were increased in septic mice, but antigen-specific primary antibody production was strongly impaired. We found that two days after CLP, CD11b(+) splenocytes were activated as demonstrated by the increased expression of activation markers, expression of arginase and production of NO by immature myeloid cells. The in vivo clearance of a bacterial infection was not impaired. DCs demonstrated reduced IL-12 production and altered antigen presentation, resulting in decreased proliferation but enhanced IFN-γ production by CD4(+) cells. CD4(+) T cells from mice immunized on day 2 after CLP showed reduced Th1 and Th2 cytokine production. In addition, there was an increase in Treg cells. Interestingly, levels of immature B cells decreased but levels of mature B cells increased two days after CLP. However, adoptive transfer of naïve CD4(+) T cells, naïve B cells, or naïve DCs did not rescue the antigen-specific antibody response.

Humanized tumor mice--a new model to study and manipulate the immune response in advanced cancer therapy

The immunological impact on antibody-based anticancer therapies remains incompletely understood due to the lack of appropriate animal models for in vivo analysis. Here, we present a novel humanized tumor mouse (HTM) model, generated by concurrent transplantation of human hematopoietic stem cells (HSCs) and human breast cancer cells in neonatal NOD-scid IL2Rγ(null) mice. Five weeks after intrahepatic transplantation, a functional human immune system was developed in all organs, and, in addition, tumor cells were detectable in lung and bone marrow (early dissemination). After 3 months posttransplant, tumor-cell effusions and macroscopic tumors associated with liver or spleen were found. Furthermore, disseminated cells in different lymphoid and nonlymphoid organs were measurable. Tumor growth was accompanied by specific T-cell maturation and tumor cell-specific T-cell activation. In addition, Natural-Killer cell accumulation and activation were observed in HTM, which was further enhanced upon IL-15 treatment facilitating the possibility of immune cell modulation in, e.g., antibody-dependent cellular cytotoxicity-based immunotherapeutic approaches. This novel mouse model makes it possible to combine transfer of MHC mismatched tumor cells together with human HSCs resulting in a solid coexistence and interaction without evidence for rejection. Overall, humanized tumor mice represent a powerful in vivo model that for the first time permits the investigation of human immune system-related target cancer therapy and resistance.

Lymphotoxin-β receptor activation by lymphotoxin-α(1)β(2) and LIGHT promotes tumor growth in an NFκB-dependent manner

Lymphotoxin beta receptor (LTβR) activation on mouse fibrosarcoma cells (BFS-1) results in enhanced solid tumor growth paralleled by increased angiogenesis induced by the expression of pro-angiogenic CXCL2. In our study, we demonstrate that both functional ligands of the LTβR, namely LTα(1) β(2) and LIGHT, are involved in the activation of LTβR in solid fibrosarcomas. To identify whether the lymphocyte population is involved in the activation of LTβR in these fibrosarcoma tumors, we used conditional LTβ-deficient mice that specifically lack LTβ expression either on T cells (T-LTβ(-/-)) or on B cells (B-LTβ(-/-)). Solid tumor growth was reduced in both mouse strains when compared to tumor growth in wild-type mice, indicating the participation of both T and B host lymphocytes in the activation of LTβR in these tumors. Tumor growth was also reduced in LIGHT-deficient mice, suggesting a contribution of this ligand to the activation of LTβR in BFS-1 fibrosarcomas. LTβR signaling can involve IκBα and/or NFκB-inducing kinase (NIK) for subsequent NFκB activation in different types of cells. Expression of a dominant negative form of IκBα or of a dominant negative mutant of NIK resulted in decreased activation of NFκB signaling and reduced expression of pro-angiogenic CXCL2 in vitro. Moreover, expression of dominant negative form of NIK or an IκBα repressor in these fibrosarcoma cells resulted in reduced solid tumor growth in vivo, suggesting that both IκBα and NIK are involved in pro-angiogenic signaling after LTβR activation. Our data support the idea that the ablation of LTβR signaling should be considered for cancer treatment.

Increased inflammation and lethality of Dusp1-/- mice in polymicrobial peritonitis models

The mitogen-activated protein kinase phosphatase Dusp1 (also known as MKP-1) is essential for control of the inflammatory response to systemic challenge with the lipopolysaccharide of Gram-negative bacteria. Here, we have investigated the consequences of Dusp1-deficiency in colon ascendens stent peritonitis (CASP) and caecal ligation and puncture (CLP), two mouse models of septic peritonitis. Following CASP, Dusp1(-/-) mice had increased serum levels of CCL4, interleukin-10 (IL-10) and IL-6, with differences from wild-type mice being dependent on severity of sepsis. These cytokines, along with inducible nitric oxide synthase messenger RNA, were also expressed at higher levels in spleen and liver. Similar over-production of these cytokines was detected in the CLP model, with even larger differences from wild-type mice. Despite the increased inflammatory response, bacterial clearance was impaired in Dusp1(-/-) mice subjected to CASP and CLP. Dusp1(-/-) mice suffered increased lethality in both peritonitis models. Together our data indicate that exaggerated inflammatory responses to gut bacteria introduced into the peritoneum in the absence of Dusp1 do not help to control bacterial replication but are detrimental for the host.

Chronic psychosocial stress promotes systemic immune activation and the development of inflammatory Th cell responses

Recent studies indicate that chronic psychosocial stress favors the development of generalized immune dysfunction. During stressor exposure neuroendocrine factors affect numbers and functionality of leukocytes. However, the exact mechanisms leading to systemic changes in immune functions during stress are still not clear. During chronic subordinate colony housing, a model of chronic psychosocial stress, mice developed spontaneous colonic inflammation. Decreased glucocorticoid signaling, induced by a combination of adrenal insufficiency and glucocorticoid resistance, was thought to prevent tempering of local immune cells, and to promote tissue inflammation. In this study we investigated changes in the systemic immune status after chronic subordinate colony housing and analyzed potential mechanisms underlying those alterations. Analysis of T helper cell subsets in peripheral lymph nodes revealed a reduction of regulatory T cells, accompanied by increased T cell effector functions. Generalized activation of T cells was shown by elevated cytokine production upon stimulation. In addition, we observed no apparent shift towards T helper type 2 responses. It is likely, that the previously reported hypocorticism in this stress model led to a steady production of inflammatory Th1, Th2, and Th17 cytokines and obstructed the shift towards an anti-inflammatory response. In conclusion, we established chronic subordinate colony housing as a model to investigate the outcome of stress on the systemic immune status. We also provide evidence that distinct T helper cell subtypes react differentially to the suppressive effect of glucocorticoids.

Neutralization of LIGHT ameliorates acute dextran sodium sulphate-induced intestinal inflammation

Emerging data indicate that alterations in the expression of tumour necrosis factor (TNF) superfamily members play a crucial role in the pathogenesis of intestinal inflammation. Recent results demonstrated that sustained transgenic expression of lymphotoxin-like inducible protein that competes with glycoprotein D for binding herpesvirus entry mediator on T cells (LIGHT; TNFSF14) induced severe intestinal inflammation, suggesting a specific role of LIGHT-mediated signalling to the intestinal compartment. In order to dissect the role of LIGHT in intestinal inflammation, we used LIGHT-deficient mice in the mouse model of acute dextran sodium sulphate-induced colitis. Interestingly, LIGHT-deficient mice were characterized by strongly reduced signs of intestinal inflammation compared with wild-type mice in this experimental model. Determination of mouse LIGHT mRNA expression in colon tissues of wild-type mice revealed a strong induction of mouse LIGHT mRNA expression during acute DSS-induced colitis. We therefore generated anti-mouse LIGHT monoclonal antibodies in LIGHT-deficient mice which bind specifically to LIGHT and are capable of neutralizing the activity of LIGHT in vitro and in vivo. With these antibodies, we demonstrated that neutralization of LIGHT during acute DSS-induced colitis resulted in reduced signs of intestinal inflammation. These data suggest that LIGHT is an important mediator in intestinal inflammation and may serve as a new target for therapeutic intervention.

Upregulation of TNF receptor type 2 in human and experimental renal allograft rejection

An important role of TNF interacting with TNFR2 has been shown in different models of ischemic, nephrotoxic and immune-mediated renal injury. To systematically evaluate the expression of TNFR2 in renal allograft rejection, we investigated human renal allograft biopsies and, in addition, established an experimental transplantation model in rats to verify the human data under standardized conditions. The expression of TNFR2 was analyzed in 96 human renal allograft biopsies with different disease entities. In a 6-day and a 28-day experimental protocol, TNFR2 was examined in kidney specimens and in the urine of control, uni-nephrectomized and transplanted rats +/- cyclosporine treatment (n = 114). In human biopsies and in rat allografts on day 6 with acute allograft rejection, significantly elevated expression of TNFR2 was observed in tubular epithelial cells, podocytes, B cells and monocytes/macrophages. The expression level was associated with renal function. The TNFR2 expression level at day 28 was significantly lower compared to day 6. TNFR2 is markedly upregulated both in human and experimental acute renal allograft rejection. Our data are robust and consistent between different species, suggesting a role for TNFR2 in the early course of rejection.

Single-chain TNF, a TNF derivative with enhanced stability and antitumoral activity

The inflammatory and proapoptotic cytokine TNF possesses a compelling potential as an antitumoral therapeutic agent. Possible target cells include the malignant cells themselves, the tumor vasculature, or the immune system. As the clinical use of TNF is limited by systemic toxicity, targeting strategies using TNF-based fusion proteins are currently used. A major obstacle, however, is that homotrimeric TNF ligands are prone to activity loss due to dissociation into their monomers. In this study, we report the construction of single-chain TNF molecule, a TNF mutant consisting of three TNF monomers fused by short peptide linkers. In comparison to wild-type TNF, single-chain TNF was found to possess increased stability in vitro and in vivo, displayed reduced systemic toxicity yet slightly enhanced antitumoral activity in mouse models. Creation of single-chain variants is a new approach for improvement of functional activity of therapeutics based on TNF family ligands.

Properdin plays a protective role in polymicrobial septic peritonitis

Properdin is a positive regulator of complement activation so far known to be instrumental in the survival of infections with certain serotypes of Neisseria meningitidis. We have generated a fully backcrossed properdin-deficient mouse line by conventional gene-specific targeting. In vitro, properdin-deficient serum is impaired in alternative pathway-dependent generation of complement fragment C3b when activated by Escherichia coli DH5alpha. Properdin-deficient mice and wild-type littermates compare in their levels of C3 and IgM. In an in vivo model of polymicrobial septic peritonitis induced by sublethal cecal ligation and puncture, properdin-deficient mice appear immunocompromised, because they are significantly impaired in their survival compared with wild-type littermates. We further show that properdin localizes to mast cells and that properdin has the ability to directly associate with E. coli DH5alpha. We conclude that properdin plays a significant role in the outcome of polymicrobial sepsis.

Tracing functional antigen-specific CCR6 Th17 cells after vaccination

Background

The function of T helper cell subsets in vivo depends on their location, and one hallmark of T cell differentiation is the sequential regulation of migration-inducing chemokine receptor expression. CC-chemokine receptor 6 (CCR6) is a trait of tissue-homing effector T cells and has recently been described as a receptor on T helper type 17 (Th17) cells. Th17 cells are associated with autoimmunity and the defence against certain infections. Although, the polarization of Th cells into Th17 cells has been studied extensively in vitro, the development of those cells during the physiological immune response is still elusive.

Methodology/Principal Findings

We analysed the development and functionality of Th17 cells in immune-competent mice during an ongoing immune response. In naïve and vaccinated animals CCR6⁺ Th cells produce IL-17. The robust homeostatic proliferation and the presence of activation markers on CCR6⁺ Th cells indicate their activated status. Vaccination induces antigen-specific CCR6⁺ Th17 cells that respond to in vitro re-stimulation with cytokine production and proliferation. Furthermore, depletion of CCR6⁺ Th cells from donor leukocytes prevents recipients from severe disease in experimental autoimmune encephalomyelitis, a model for multiple sclerosis in mice.

Conclusions/Significance

In conclusion, we defined CCR6 as a specific marker for functional antigen-specific Th17 cells during the immune response. Since IL-17 production reaches the highest levels during the immediate early phase of the immune response and the activation of Th17 cells precedes the Th1 cell differentiation we tent to speculate that this particular Th cell subset may represent a first line effector Th cell subpopulation. Interference with the activation of this Th cell subtype provides an interesting strategy to prevent autoimmunity as well as to establish protective immunity against infections.

Cutting edge: expression of TNFR2 defines a maximally suppressive subset of mouse CD4+CD25+FoxP3+ T regulatory cells: applicability to tumor-infiltrating T regulatory cells

TNFR2 is predominantly expressed by a subset of human and mouse CD4(+)CD25(+)FoxP3(+) T regulatory cells (Tregs). In this study, we characterized the phenotype and function of TNFR2(+) Tregs in peripheral lymphoid tissues of normal and tumor-bearing C57BL/6 mice. We found that TNFR2 was expressed on 30-40% of the Tregs of the peripheral activated/memory subset that were most highly suppressive. In contrast, TNFR2(-) Tregs exhibited the phenotype of naive cells and only had minimal suppressive activity. Although not typically considered to be Tregs, CD4(+)CD25(-)TNFR2(+) cells nevertheless possessed moderate suppressive activity. Strikingly, the suppressive activity of TNFR2(+) Tregs was considerably more potent than that of reportedly highly suppressive CD103(+) Tregs. In the Lewis lung carcinoma model, more highly suppressive TNFR2(+) Tregs accumulated intratumorally than in the periphery. Thus, TNFR2 identifies a unique subset of mouse Tregs with an activated/memory phenotype and maximal suppressive activity that may account for tumor-infiltrating lymphocyte-mediated immune evasion by tumors.

TNF: a moonlighting protein at the interface between cancer and infection

The remarkable ability of TNF, especially in combination with Interferon-gamma or melphalan, to inhibit the growth of malignant tumor cells is so far unmatched. Unfortunately, its high systemic toxicity and hepatotoxicity prevent its systemic use in cancer patients. An elegant manner to circumvent this problem is the isolated limb and liver perfusion for the treatment of melanoma, soft tissue sarcoma and liver tumors, respectively, although the latter method can lead to a reversible hepatotoxicity. In order to allow also the treatment of other cancers with TNF, new strategies have to be developed that aim at sensitizing tumor cells to TNF and at reducing its systemic and liver toxicity, without losing its antitumor efficiency. Moreover, the lectin-like domain of TNF, which is spatially distinct from the receptor binding sites, could be useful in reducing cancer treatment-related pulmonary edema formation. This review will discuss some recent developments in these areas, which can lead to a renewed interest in TNF for the systemic treatment of cancer.

Ficolins: novel pattern recognition molecules of the innate immune response

Ficolins are members of the collectin family of proteins which are able to recognize pathogen-associated molecular pattern (PAMP) on microbial surfaces. Upon binding to their specific PAMP, ficolins may trigger activation of the immune system by either binding to cellular receptors for collectins or by initiating activation of complement via the lectin pathway. For the latter, the human ficolins (i.e. L-, H- and M-ficolin) and murine ficolin-A were shown to associate with the lectin pathway-specific serine protease MBL-associated serine protease-2 (MASP-2) and catalyse its activation which in turn activates C4 and C4b-bound C2 to generate the C3 convertase C4b2a. There is mounting evidence underlining the lectin nature of ficolins with a wide range of carbohydrate moieties recognized on microbial surfaces. However, not all members of the ficolin family appear to act as lectin pathway recognition components. For example, murine ficolin-B does not associate with MASP-2 and appears to be absent in plasma and other humoral fluids. Its stringent cellular localization points to other functions within the immune response, possibly acting as an intracellular scavenger to target and facilitate clearance of PAMP-bearing debris. When comparing ficolin orthologues from different species, it appears evident that human, murine, and porcine ficolins differ in many aspects, a specific point that we aim to address in this review.

Advances in sepsis research derived from animal models

Inflammation is the basic process by which tissues of the body respond to infection. Activation of the immune system normally leads to removal of microbial pathogens, and after resolution of the inflammation immune homeostasis is restored. This controlled process, however, can be disturbed resulting in disease. Therefore, many studies using infection models have investigated the participating immune mechanisms aiming at possible therapeutic interventions. Defined model substances such as bacterial lipopolysaccharide (endotoxin) have been used to mimic bacterial infections and analyze their immune stimulating functions. A complex network of molecular mechanisms involved in the recognition and activation processes of bacterial infections and their regulation has developed from these studies. More complex infection models will now help to interpret earlier observations leading to the design of relevant new infection models.

Characterization of TNF receptor type 2 isoform in the mouse

In this report a TNF receptor type 2 (TNFR2) isoform in the mouse, termed micp75TNFR, was compared to its human orthologue hicp75TNFR and to the known mouse TNFR2. The micp75TNFR is generated by the use of an alternative transcriptional start site within the mouse TNFR2 gene. This receptor isoform was found to be expressed in different macrophage-like and endothelial tumor cell lines and mouse spleen cells after stimulation. Lacking the leader sequence and part of the amino-terminal end of the mature TNFR2, the micp75TNFR was characterized by mainly intracellular expression. In contrast to its human paralogue, the micp75TNFR lacked the capacity to bind TNF. Therefore, micp75TNFR expression did not mediate protection from TNF-induced cytotoxicity but may interfere with TNFR2 signalling.

Blocking lymphotoxin beta receptor signalling exacerbates acute DSS-induced intestinal inflammation--opposite functions for surface lymphotoxin expressed by T and B lymphocytes

The lymphotoxin beta receptor (LTbetaR) signalling pathway is involved in the development of secondary lymphoid organs and the maintenance of organized lymphoid tissues. Additionally, previous studies clearly demonstrated the involvement of the LTbetaR interaction with its ligands in promoting intestinal inflammation. In order to dissect the role of LTbetaR activation in the mouse model of acute DSS-induced colitis we treated mice with a functional inhibitor of LTbetaR activation (LTbetaR:Ig) and compared it to disease in LTbetaR-deficient and LTalphabeta-deficient mice. All these modes of LTbetaR signalling ablation resulted in significant aggravation of the disease and in release of inflammatory cytokines such as TNF, IL-6, and IFNgamma. Finally, using mice with conditionally ablated expression of membrane bound LTbeta on T or B cells, respectively, distinct and opposite contributions of surface LTbeta expressed on T or B cells was found. Thus, activation of LTbetaR by LTalphabeta mainly expressed on T lymphocytes is crucial for the down regulation of the inflammatory response in this experimental model.

Interaction of TNF with TNF Receptor Type 2 Promotes Expansion and Function of Mouse CD4+CD25+ T Regulatory Cells

Although TNF is a major proinflammatory cytokine, increasing evidence indicates that TNF also has immunosuppressive feedback effects. We have demonstrated in this study that, in both resting and activated states, mouse peripheral CD4(+)CD25(+) T regulatory cells (Tregs) expressed remarkably higher surface levels of TNFR2 than CD4(+)CD25(-) T effector cells (Teffs). In cocultures of Tregs and Teffs, inhibition of proliferation of Teffs by Tregs was initially transiently abrogated by exposure to TNF, but longer exposure to TNF restored suppressive effects. Cytokine production by Teffs remained continually suppressed by Tregs. The profound anergy of Tregs in response to TCR stimulation was overcome by TNF, which expanded the Treg population. Furthermore, in synergy with IL-2, TNF expanded Tregs even more markedly up-regulated expression of CD25 and FoxP3 and phosphorylation of STAT5, and enhanced the suppressive activity of Tregs. Unlike TNF, IL-1beta and IL-6 did not up-regulate FoxP3-expressing Tregs. Furthermore, the number of Tregs increased in wild-type mice, but not in TNFR2(-/-) mice following sublethal cecal ligation and puncture. Depletion of Tregs significantly decreased mortality following cecal ligation and puncture. Thus, the stimulatory effect of TNF on Tregs resembles the reported costimulatory effects of TNF on Teffs, but is even more pronounced because of the higher expression of TNFR2 by Tregs. Moreover, our study suggests that the slower response of Tregs than Teffs to TNF results in delayed immunosuppressive feedback effects.

Investigations on the Involvement of the Lectin Pathway of Complement Activation in Anaphylaxis

BACKGROUND

Systemic anaphylaxis is the most severe form of immediate hypersensitivity reaction. The activation of the complement system occurs during anaphylactic shock. The purpose of this study was to determine in a mouse model whether the lectin pathway of complement activation is involved in anaphylaxis.

METHODS

To see whether the lectin pathway is involved in anaphylactic shock, serum mannan-binding lectin (MBL) levels were measured after passive anaphylaxis. Also MBL expression and binding to potential ligands were investigated. To determine whether complement or mast cell activation is essential for hypothermia in anaphylactic shock, mouse strains deficient in MBL-A and MBL-C, C1q, factors B and C2, C5, C5aR, or mast cells were tested.

RESULTS

After antigenic challenge a marked drop in body temperature as well as a rapid decrease in serum MBL levels were observed. The decrease of serum MBL levels in shock could not be attributed to MBL binding to immune complexes or tissues, but an interaction of MBL with mast cell-derived proteoglycans was seen. In contrast to mast cell-deficient mice, none of the complement-deficient mouse strains were protected from shock-associated hypothermia.

CONCLUSIONS

These results indicate that neither MBL nor activation of the complement cascade is crucial for the induction of anaphylaxis. In contrast mast cell activation is associated with the development of hypothermia and possibly the observed decrease in serum MBL levels.

Localization of the mouse defense lectin ficolin B in lysosomes of activated macrophages

Ficolins are pattern-recognition molecules of the innate immune system able to trigger the lectin pathway of the complement activation upon binding to microbial surfaces. In humans, two plasma ficolins have been identified and characterized, whereas a third cell-associated ficolin (M-ficolin) was found on monocyte surfaces. The mouse homologue of M-ficolin is called ficolin B. Although the spatial-temporal expression patterns of mouse ficolins have been described recently, the subcellular localization of ficolin B protein is so far unknown. By using ficolin B-specific antibodies and confocal microscopy, we show that ficolin B is expressed within mouse peritoneal exudate macrophages and is co-localized with Lamp-1, a marker for lysosomes and late endosomes. In addition, the data indicate that ficolin B expression is up-regulated upon macrophage activation.

Improved resistance to bacterial superinfection in mice by treatment with macrophage migration inhibitory factor

Nosocomial infections in immune-suppressed patients are a widespread problem in intensive care medicine. Such patients are highly susceptible to infections because their immune defenses are impaired and, therefore, unable to adequately combat invading microorganisms. To investigate the problem of sepsis-induced immune suppression, we used a model in which mice developed sublethal peritonitis induced by cecal ligation and puncture (CLP). Two days after CLP mice were in an immune-suppressed state, as measured by impaired capacity to produce tumor necrosis factor (TNF) and enhanced susceptibility to bacterial infections. Since macrophage migration inhibitory factor (MIF) is a critical mediator of septic shock by modulation of innate immune responses, the role of MIF in sepsis-induced immune suppression was analyzed. Neutralization of endogenous MIF further enhanced susceptibility to bacterial superinfection after CLP. Conversely, treatment with recombinant human MIF before the bacterial superinfection protected the animals. MIF treatment reconstituted the impaired capacity to produce proinflammatory cytokines, such as TNF and interleukin-6. This study indicates that MIF might be able to ameliorate the sepsis-induced immune suppression by reenabling the organism to react adequately to a secondary bacterial challenge.

Requirement of TNF and TNF receptor type 2 for LPS-induced protection from lethal septic peritonitis

Pretreatment of mice with low quantities of LPS induces endotoxin tolerance characterized by enhanced resistance to lethal doses of LPS and to a number of infectious challenges. Mice subjected to cecal ligation and puncture (CLP) survived the ensuing septic peritonitis significantly better when they had been pretreated with LPS. This LPS-induced protection was dependent on endogenous TNF production capacity since LPS pretreatment did not protect TNF-deficient mice from death after CLP. While mice deficient in the TNF receptor type 2 (p75TNFR) were as sensitive to CLP-induced mortality as control mice, LPS pretreatment could not reduce mortality in p75TNFR-deficient mice after CLP. Therefore, activation of the TNF receptor type 2 by endogenous TNF constitutes an important interaction for the development of LPS-induced resistance to bacterial infection.

Failure of interferon-gamma and tumor necrosis factor in mediating anemia of chronic disease in a mouse model of protracted septic peritonitis

Interferon-gamma (IFN-gamma) is considered one of the main inflammatory cytokines contributing to the generation of anemia of chronic disease (ACD). In this study, we used a previously described murine model for ACD based on sublethal cecal ligation and puncture (CLP) with ensuing protracted peritonitis. Within 2 weeks after CLP, a moderate normochromic anemia with low serum iron concentration and preserved iron stores develops, which is consistent with ACD. In order to determine whether IFN-gamma contributes to the development of ACD in vivo, we neutralized IFN-gamma after CLP shortly before and during the phase of most severe bone marrow depression in order to prevent anemia. Additionally, we studied IFN-gamma receptor-deficient mice that underwent CLP. Two weeks after CLP, we determined the red blood cell count, hemoglobin concentration, hematocrit, serum iron concentration, and iron stores in spleens of wild-type mice, IFN-gamma receptor-deficient mice, and mice after neutralization of IFN-gamma. Neutralization of IFN-gamma after CLP could not prevent mice from becoming anemic. Accordingly, IFN-gamma receptor-deficient mice developed anemia to the same extent as wild-type mice. Serum iron concentration was lowered both in IFN-gamma receptor-deficient and wild-type mice. Iron stores in untreated IFN-gamma receptor-deficient mice were elevated compared to untreated wild-type mice. After CLP both IFN-gamma receptor-deficient and wild-type mice had equally overloaded iron stores. Additional neutralization of TNF in IFN-gamma receptor-deficient mice also did not attenuate CLP-induced anemia. Our results clearly demonstrate that neither IFN-gamma alone nor in combination with TNF is a mediator of ACD in our model with transient anemia induced by protracted septic peritonitis.

Divergence of protection induced by bacterial products and sepsis-induced immune suppression

Susceptibility to bacterial infections after a primary immune stimulation differs drastically depending on the presensitization of the innate immune system. To determine the conditions that either induce protection or enhanced susceptibility to infection with Salmonella enterica serovar Typhimurium, we pretreated mice either with tumor necrosis factor (TNF), whole killed bacteria, or sublethal cecal ligation and puncture (CLP) as a mouse model for septic peritonitis. Impaired production of the cytokines TNF, interleukin-6 (IL-6), and IL-10 was induced by these pretreatment schedules, with TNF-signaling not being essential for this effect. Injection of TNF or killed bacteria enhanced survival of mice infected subsequently with serovar Typhimurium. In contrast, sepsis such as that induced by CLP only protected from shock induced by d-galactosamine and lipopolysaccharide or by a high dose of bacteria but sensitized to a secondary bacterial infection. Such sepsis-induced enhanced susceptibility to infection was critically dependent on TNF function.

Colocalization of endogenous TNF with a functional intracellular splice form of human TNF receptor type 2

Background

Tumor necrosis factor (TNF) is a pleiotropic cytokine involved in a broad spectrum of inflammatory and immune responses including proliferation, differentiation, and cell death. The biological effects of TNF are mediated via two cell surface TNF receptors: p55TNFR (TNFR1; CD120a) and p75TNFR (TNFR2; CD120b). Soluble forms of these two receptors consisting of the extracellular domains are proteolytically cleaved from the membrane and act as inhibitors. A novel p75TNFR isoform generated by the use of an additional transcriptional start site has been described and was termed hicp75TNFR. We focused on the characterization of this new isoform as this protein may be involved in chronic inflammatory processes.

Methods

Cell lines were retroviraly transduced with hp75TNFR isoforms. Subcellular localization and colocalization studies with TNF were performed using fluorescence microscopy including exhaustive photon reassignment software, flow cytometry, and receptosome isolation by magnetic means. Biochemical properties of the hicp75TNFR were determined by affinity chromatography, ELISA, and western blot techniques.

Results

We describe the localization and activation of a differentially spliced and mainly intracellularly expressed isoform of human p75TNFR, termed hicp75TNFR. Expression studies with hicp75TNFR cDNA in different cell types showed the resulting protein mostly retained in the trans-Golgi network and in endosomes and colocalizes with endogenous TNF. Surface expressed hicp75TNFR behaves like hp75TNFR demonstrating susceptibility for TACE-induced shedding and NFκB activation after TNF binding.

Conclusion

Our data demonstrate that intracellular hicp75TNFR is not accessible for exogenously provided TNF but colocalizes with endogenously produced TNF. These findings suggest a possible intracellular activation mechanism of hicp75TNFR by endogenous TNF. Subsequent NFκB activation might induce anti-apoptotic mechanisms to protect TNF-producing cells from cytotoxic effects of TNF. In addition, the intracellular and not TACE-accessible splice form of the hp75TNFR could serve as a pool of preformed, functional hp75TNFR.

Treatment of experimental sepsis-induced immunoparalysis with TNF

Following a severe septic abdominal infection induced by sublethal cecal ligation and puncture (CLP) in mice, a phase of depressed immune reactivity occurred two days after CLP characterized by a reduced capacity to produce TNF. To determine whether this reduced TNF production causes immunoparalysis as determined by increased susceptibility to bacterial infection and whether therapeutic TNF substitution can be beneficial during this phase, a super-infection with Salmonella enterica Serovar typhimurium or Listeria monocytogenes was induced two days after sublethal CLP. After CLP a state of true immunoparalysis developed during which Salmonella or Listeria super-infection led to increased lethality paralleled by increased bacterial numbers in spleens and livers. Injection of recombinant human TNF before or at the time of super-infection conferred protection to Salmonella but not to Listeria. In the latter case, the infection mortality was even enhanced. Thus, super-infection during the state of sepsis-induced immunoparalysis leads to increased lethality. TNF substitution during this state of immunoparalysis can be beneficial or deleterious, depending on the location of TNF activity in the animal, timing of TNF administration, or the type of super-infection. These results demonstrate that impaired TNF production capacity can account for some aspects of immunoparalysis, however, diagnostic parameters are required for a safe TNF substitution therapy.

Involvement of the lectin pathway of complement activation in antimicrobial immune defense during experimental septic peritonitis

A critical first line of defense against infection is constituted by the binding of natural antibodies to microbial surfaces, activating the complement system via the classical complement activation pathway. In this function, the classical activation pathway is supported and amplified by two antibody-independent complement activation routes, i.e., the lectin pathway and the alternative pathway. We studied the contribution of the different complement activation pathways in the host defense against experimental polymicrobial peritonitis induced by cecal ligation and puncture by using mice deficient in either C1q or factors B and C2. The C1q-deficient mice lack the classical complement activation pathway. While infection-induced mortality of wild-type mice was 27%, mortality of C1q-deficient mice was increased to 60%. Mice with a deficiency of both factors B and C2 lack complement activation via the classical, the alternative, and the lectin pathways and exhibit a mortality of 92%, indicating a significant contribution of the lectin and alternative pathways of complement activation to survival. For 14 days after infection, mannan-binding lectin (MBL)-dependent activation of C4 was compromised. Serum MBL-A and MBL-C levels were significantly reduced for 1 week, possibly due to consumption. mRNA expression profiles did not lend support for either of the two MBL genes to respond as typical acute-phase genes. Our results demonstrate a long-lasting depletion of MBL-A and MBL-C from serum during microbial infection and underline the importance of both the lectin and the alternative pathways for antimicrobial immune defense.

Lymphotoxin-beta receptor activation by activated T cells induces cytokine release from mouse bone marrow-derived mast cells

Lymphotoxin-beta receptor (LTbetaR) signaling is known to play a key role in embryonic lymphoid organ formation as well as maintenance of lymphoid architecture. Activation of the LTbetaR is induced by either the heterotrimeric lymphotoxin-alpha(1)beta(2) (LTalpha(1)beta(2)) or the homotrimeric LIGHT (homologous to lymphotoxins, exhibits inducible expression, and competes with HSV gpD for herpes virus entry mediator, a receptor expressed by T lymphocyte). Both ligands are expressed on activated lymphocytes. As mast cells reside in close proximity to activated T cells in some inflammatory tissues, we examined the expression of LTbetaR on bone marrow-derived mast cells and asked whether the LTbetaR-ligand interaction would allow communication between mast cells and activated T cells. We found that mast cells express LTbetaR at the mRNA as well as at the protein level. To investigate LTbetaR-specific mast cell activation, the LTbetaR on BMMC from either wild-type or LTbetaR-deficient mice was stimulated with recombinant mouse LIGHT or agonistic mAbs in the presence of ionomycin. LTbetaR-specific release of the cytokines IL-4, IL-6, TNF, and the chemokines macrophage inflammatory protein 2 and RANTES was detected. Moreover, coculture of mast cells with T cells expressing the LTbetaR ligands also entailed the release of these cytokines. Interference with a specific LTbetaR inhibitor resulted in significant suppression of mast cell cytokine release. These data clearly show that LTbetaR expressed on mast cells can transduce a costimulatory signal in T cell-dependent mast cell activation.

From “Junk” to Gene: Curriculum vitae of a Primate Receptor Isoform Gene

Exonization of Alu retroposons awakens public opinion, particularly when causing genetic diseases. However, often neglected, alternative "Alu-exons" also carry the potential to greatly enhance genetic diversity by increasing the transcriptome of primates chiefly via alternative splicing.Here, we report a 5' exon generated from one of the two alternative transcripts in human tumor necrosis factor receptor gene type 2 (p75TNFR) that contains an ancient Alu-SINE, which provides an alternative N-terminal protein-coding domain. We follow the primate evolution over the past 63 million years to reconstruct the key events that gave rise to a novel receptor isoform. The Alu integration and start codon formation occurred between 58 and 40 million years ago (MYA) in the common ancestor of anthropoid primates. Yet a functional gene product could not be generated until a novel splice site and an open reading frame were introduced between 40 and 25 MYA on the catarrhine lineage (Old World monkeys including apes).

Blocking lymphotoxin-beta receptor activation diminishes inflammation via reduced mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expression and leucocyte margination in chronic DSS-induced colitis

The lymphotoxin-beta receptor (LTbetaR) pathway is critical for maintenance of organized lymphoid structures and is involved in the development of colitis. To investigate the mechanisms by which LTbetaR activation contributes to the pathology of chronic inflammation we used a soluble LTbetaR-Ig fusion protein as a competitive inhibitor of LTbetaR activation in the mouse model of chronic colitis induced by oral administration of dextran sulphate sodium. Strong expression of LTbeta which constitutes part of the LTalpha(1)beta(2) ligand complex was detected in colonic tissue of mice with chronic colitis. Treatment with LTbetaR-Ig significantly attenuated the development and histological manifestations of the chronic inflammation and reduced the production of inflammatory cytokines such as TNF, IL-1beta, and IL-6. Moreover, LTbetaR-Ig treatment significantly down-regulated mucosal addressin cell adhesion molecule-1 (MAdCAM-1) expression, leading to reduced leucocyte rolling and sticking in postcapillary and collecting venules and reduced extravasation into the intestinal mucosa as quantified by in vivo fluorescence microscopy. Thus, LTbetaR pathway inhibition ameliorates DSS-induced experimental chronic colitis in mice by MAdCAM-1 down-regulation entailing reduced lymphocyte margination and extravasation into the inflamed mucosa. Therefore, a combined treatment with reagents blocking T cell-mediated perpetuation of chronic inflammation such as LTbetaR-Ig together with direct anti-inflammatory reagents such as TNF inhibitors could constitute a promising treatment strategy for chronic colitis.