IL-10 signaling in dendritic cells is required for tolerance induction in a murine model of allergic airway inflammation.

Allergen specific tolerance induction efficiently ameliorates subsequent allergen induced inflammatory responses. The underlying regulatory mechanisms have been attributed mainly to interleukin (IL)-10 produced by diverse hematopoietic cells, while targets of IL-10 in allergen specific tolerance induction have not yet been well defined. Here, we investigate potential cellular targets of IL-10 in allergen specific tolerance induction using mice with a cell type specific inactivation of the IL-10 receptor gene. Allergic airway inflammation was effectively prevented by tolerance induction in mice with IL-10 receptor (IL-10R) deficiency in T or B cells. Similarly, IL-10R on monocytes/macrophages and/or neutrophils was not required for tolerance induction. In contrast, tolerance induction was impaired in mice that lack IL-10R on dendritic cells: those mice developed an allergic response characterized by a pronounced neutrophilic lung infiltration, which was not ameliorated by tolerogenic treatment. In conclusion, our results show that allergen specific tolerance can be effectively induced without a direct impact of IL-10 on cells of the adaptive immune system, and highlight dendritic cells, but not macrophages nor neutrophils, as the main target of IL-10 during tolerance induction.

Evolution of Immunity and Pathogens.

Host and pathogen engage in a constant evolutionary struggle known as a "Red Queen Paradigm". In this struggle, natural selection favours the pathogen which evolves effective virulence mechanisms and the host which is able to field adequate resistance strategies. A number of factors limit what each side can do. These include the fact that the elaboration of virulence or resistance mechanisms results in costs in genetic fitness and requires the use of ever more of the limited number of genes available in the genome. In addition, since the pathogen usually has a very much shorter generation time than the host, it can fix new virulence mutations much more quickly than the host can evolve matching resistance mechanisms. Finally, the host must ensure that its defence system does not result in unacceptable levels of collateral damage to its own tissues. This chapter briefly outlines how these considerations shape host-pathogen interactions.

IL-10 acts as a developmental switch guiding monocyte differentiation to macrophages during a murine peritoneal infection.

The peritoneal wash of BALB/c or C57BL/6 mice contains two populations of macrophages that differ in their level of expression of MHC class II (MHC II). Although both populations efficiently phagocytose bacteria in vivo, only the MHC II(lo) population is effective at phagocytosing apoptotic cells in vivo and only the MHC II(hi) population is effective at presenting Ag to T cells in vitro. Soon after induction of a peritoneal infection both of these macrophage populations are lost from the peritoneal wash fraction. Blood monocytes then enter the inflamed peritoneum and develop into new peritoneal macrophages. Whether these monocytes develop into MHC II(lo) or into MHC II(hi) macrophages is crucially dependent on the cytokine IL-10, which is transiently elevated in the peritoneal wash during the early phase of infection. Monocytes from CD45.1 animals transferred early in infection when the IL-10 concentration is high into congenic CD45.2 recipients develop into the MHC II(lo) macrophage population. Monocytes transferred later, when the IL-10 concentration has fallen, develop into the MHC II(hi) population. In infected IL-10-deficient animals monocytes fail to develop into the MHC II(lo) population but can be induced to do so by exogenous application of IL-10. Finally, high numbers of wild-type monocytes injected into IL-10R1-deficient animals develop into MHC II(lo) macrophages and were able by a bystander effect to induce the differentiation of the endogenous monocytes to the same fate.

Autocrine regulation of pulmonary inflammation by effector T-cell derived IL-10 during infection with respiratory syncytial virus.

Respiratory syncytial virus (RSV) infection is the leading viral cause of severe lower respiratory tract illness in young infants. Clinical studies have documented that certain polymorphisms in the gene encoding the regulatory cytokine IL-10 are associated with the development of severe bronchiolitis in RSV infected infants. Here, we examined the role of IL-10 in a murine model of primary RSV infection and found that high levels of IL-10 are produced in the respiratory tract by anti-viral effector T cells at the onset of the adaptive immune response. We demonstrated that the function of the effector T cell -derived IL-10 in vivo is to limit the excess pulmonary inflammation and thereby to maintain critical lung function. We further identify a novel mechanism by which effector T cell-derived IL-10 controls excess inflammation by feedback inhibition through engagement of the IL-10 receptor on the antiviral effector T cells. Our findings suggest a potentially critical role of effector T cell-derived IL-10 in controlling disease severity in clinical RSV infection.

Interleukin-10 signaling in regulatory T cells is required for suppression of Th17 cell-mediated inflammation.

Effector CD4+ T cell subsets, whose differentiation is facilitated by distinct cytokine cues, amplify the corresponding type of inflammatory response. Regulatory T (Treg) cells integrate environmental cues to suppress particular types of inflammation. In this regard, STAT3, a transcription factor essential for T helper 17 (Th17) cell differentiation, is necessary for Treg cell-mediated control of Th17 cell responses. Here, we showed that anti-inflammatory interleukin-10 (IL-10), and not proinflammatory IL-6 and IL-23 cytokine signaling, endowed Treg cells with the ability to suppress pathogenic Th17 cell responses. Ablation of the IL-10 receptor in Treg cells resulted in selective dysregulation of Th17 cell responses and colitis similar to that observed in mice harboring STAT3-deficient Treg cells. Thus, Treg cells limit Th17 cell inflammation by serving as principal amplifiers of negative regulatory circuits operating in immune effector cells.

Monocytes/macrophages and/or neutrophils are the target of IL-10 in the LPS endotoxemia model.

IL-10 is a potent regulator of the innate and adaptive immune responses. Several cell types produce IL-10 and its receptor chains and these may regulate different immune responses. Here we report that inactivation of the IL-10 receptor (IL-10R1) gene in mice leads to an increased susceptibility to chemically induced colitis as in the classical IL-10-deficient mutant. To identify the cells regulated by IL-10 in immune responses, we generated several cell type specific IL-10R1-deficient mutants. We show that, in an IL-10-dependent LPS model of endotoxemia, dampening of the immune response requires expression of IL-10R1 in monocytes/macrophages and/or neutrophils but not in T cells nor B cells. As the macrophage and/or neutrophil-specific IL-10-deficient mutants also display the same phenotype, our results suggest that an autocrine loop in monocytes/macrophages is the most probable mechanism for the regulation of an LPS-induced septic shock. In contrast, in an IL-10-regulated T-cell response to Trichuris muris infection, IL-10 acting on T cells or monocytes/macrophages/neutrophils is not critical for the control of the infection.

Implantation of alloplastic material increases survival of mice subsequently exposed to polymicrobial sepsis.

PURPOSE: Major surgery can modulate the immune system and by this the clinical course of following complications. Effects of minor surgical treatments on the immune system and septic complications are poorly understood. MATERIALS AND METHODS: We investigated the effect of a minor surgical procedure--the implantation of an osmotic pump--on the outcome of experimental polymicrobial sepsis (colon ascendens stent-induced peritonitis, CASP) in mice. RESULTS: Animals with pumps implanted 3 days prior to CASP showed an attenuated clinical course of sepsis and increased survival. While measured serum cytokine levels were not affected by the minor surgical stress of pump implantation, splenocyte secretion of IFN-gamma in response to lipopolysaccharide was increased. CONCLUSION: The early implantation of alloplastic material modulates the immune system and leads to an increased survival of a polymicrobial sepsis. Identifying the molecular nature of this effect might point the way to a new therapeutic approach to reduce sepsis mortality.

Selective expression of the chemokine receptor XCR1 on cross-presenting dendritic cells determines cooperation with CD8+ T cells.

The expression of the chemokine receptor XCR1 and the function of its ligand XCL1 (otherwise referred to as ATAC, lymphotactin, or SCM-1) remained elusive to date. In the present report we demonstrated that XCR1 is exclusively expressed on murine CD8(+) dendritic cells (DCs) and showed that XCL1 is a potent and highly specific chemoattractant for this DC subset. CD8(+) T cells abundantly secreted XCL1 8-36 hr after antigen recognition on CD8(+) DCs in vivo, in a period in which stable T cell-DC interactions are known to occur. Functionally, XCL1 increased the pool of antigen-specific CD8(+) T cells and their capacity to secrete IFN-gamma. Absence of XCL1 impaired the development of cytotoxicity to antigens cross-presented by CD8(+) DCs. The XCL1-XCR1 axis thus emerges as an integral component in the development of efficient cytotoxic immunity in vivo.

Evolution of immunity and pathogens.

The Cologne Spring Meeting of the Institute of Genetics focuses on a different topic each year. In Spring 2007, the meeting focused on the complex evolutionary relationships between hosts and pathogens.

Macrophages as main inducers of IFN-gamma in T cells following administration of human and mouse heat shock protein 60.

Human Hsp60 (hHsp60) elicits a potent pro-inflammatory response in cells of the innate immune system. Here we compared the capacity of peritoneal exudate cells (PEC) and bone marrow-derived dendritic cells (DC) to stimulate murine T cells in the presence of Hsp60. Hsp60 induced a specific secretion of high amounts of IFN-gamma in T cells with PEC as antigen-presenting cells (APC). Although DC are highly efficient APC, they were much less potent as inducers of IFN-gamma in the presence of Hsp60. The IFN-gamma-inducing effect of Hsp60 is dependent on co-stimulatory signals provided by B7-CD28 interactions. In addition to hHsp60, we used syngenic murine recombinant Hsp60 (mHsp60) and show that mHsp60 also induces IFN-gamma in TCR transgenic T cells. These results demonstrate that mHsp60 as an endogenous 'self' molecule can induce an inflammatory response. Interestingly, mHsp60, although sharing >98% protein sequence identity with the hHsp60 homologue, does not bind to human CD14 molecules. Taken together, our results indicate a finely tuned activation of cells from the innate and adaptive immune system by 'self' Hsp60 that depends strongly on the type of APC.

Neutrophil influx in response to a peritoneal infection with Salmonella is delayed in lipopolysaccharide-binding protein or CD14-deficient mice.

The induction of an adaptive immune response to a previously unencountered pathogen is a time-consuming process and initially the infection must be held in check by the innate immune system. In the case of an i.p. infection with Salmonella typhimurium, survival requires both CD14 and LPS-binding protein (LBP) which, together with Toll-like receptor 4 and myeloid differentiation protein 2, provide a sensitive means to detect bacterial LPS. In this study, we show that in the first hours after i.p. infection with Salmonella a local inflammatory response is evident and that concomitantly neutrophils flood into the peritoneum. This rapid neutrophil influx is dependent on TNF since it is 1) abolished in TNF KO mice and 2) can be induced by i.p. injection of TNF in uninfected animals. Neutrophil influx is not strictly dependent on the presence of either LBP or CD14. However, in their absence, no local inflammatory response is evident, neutrophil migration is delayed, and the mice succumb to the infection. Using confocal microscopy, we show that the neutrophils which accumulate in CD14 and LBP null mice, albeit with delayed kinetics, are nevertheless fully capable of ingesting the bacteria. We suggest that the short delay in neutrophil influx gives the pathogen a decisive advantage in this infection model.