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SummaryMonocytes are heterogeneous innate effector leukocytes generated in the bone marrow and released into circulation in a CCR2-dependent manner. During infection or inflammation myelopoiesis is modulated to rapidly meet demand for more effector cells. Danger signals from peripheral tissues can influence this process. Herein we demonstrate that repetitive TLR7 stimulation via the epithelial barriers drove a potent emergency bone marrow monocyte response. This process was unique to TLR7 activation and occurred independently of the canonical CCR2 and CX3CR1 axes or prototypical cytokines. The monocytes egressing the bone marrow had an immature Ly6C-high profile and differentiated into vascular Ly6C-low monocytes and tissue macrophages in multiple organs. They displayed a blunted cytokine response to further TLR7 stimulation and reduced lung viral load after RSV and influenza virus infection. These data provide insights into the emergency myelopoiesis likely to occur in response to the encounter of single-stranded RNA viruses at barrier sites.

Type 1 conventional dendritic cells (cDC1) play a critical role in priming anticancer cytotoxic CD8+ T cells. DNGR-1 (a.k.a. CLEC9A) is a cDC1 receptor that binds to F-actin exposed on necrotic cancer and normal cells. DNGR-1 signaling enhances cross-presentation of dead-cell associated antigens, including tumor antigens. We have recently shown that secreted gelsolin (sGSN), a plasma protein, competes with DNGR-1 for binding to dead cell-exposed F-actin and dampens anticancer immunity. Here, we investigated the effects of loss of sGSN on various anticancer therapies that are thought to induce cell death and provoke an immune response to cancer. We compared WT (wildtype) with Rag1–/–, Batf3–/–, Clec9agfp/gfp, sGsn–/– or sGsn–/– Clec9agfp/gfp mice implanted with transplantable tumor cell lines, including MCA-205 fibrosarcoma, 5555 BrafV600E melanoma and B16-F10 LifeAct (LA)-ovalbumin (OVA)-mCherry melanoma. Tumor-bearing mice were treated with (1) doxorubicin (intratumoral) chemotherapy for MCA-205, (2) BRAF-inhibitor PLX4720 (oral gavage) targeted therapy for 5555 BrafV600E, and (3) X-ray radiotherapy for B16 LA-OVA-mCherry. We confirmed that efficient tumor control following each therapy requires an immunocompetent host as efficacy was markedly reduced in Rag1–/– compared with WT mice. Notably, across all the therapeutic modalities, loss of sGSN significantly enhanced tumor control compared with treated WT controls. This was an on-target effect as mice deficient in both sGSN and DNGR-1 behaved no differently from WT mice following therapy. In sum, we find that mice deficient in sGsn display enhanced DNGR-1-dependent responsiveness to chemotherapy, targeted therapy and radiotherapy. Our findings are consistent with the notion some cancer therapies induce immunogenic cell death (ICD), which mobilizes anticancer T cells. Our results point to cDC1 and DNGR-1 as decoders of ICD and to sGSN as a negative regulator of such decoding, highlighting sGSN as a possible target in cancer treatment. Further prospective studies are warranted to identify patients who may benefit most from inhibition of sGSN function.

The regenerative potential of mammalian peripheral nervous system (PNS) neurons after injury is critically limited by their slow axonal regenerative rate1. Since a delayed target re-innervation leads to irreversible loss of function of target organs2, accelerated axonal regeneration is required to enhance functional outcomes following injury. Regenerative ability is influenced by both injury-dependent and injury-independent mechanisms3. Among the latter, environmental factors such as exercise and environmental enrichment have been shown to affect signalling pathways that promote axonal regeneration4. Several of these pathways, including modifications in gene transcription and protein synthesis, mitochondrial metabolism and release of neurotrophins, can be activated by intermittent fasting (IF)5,6. IF has in turn been shown to increase synaptic plasticity7,8 and neurogenesis9, partially sharing molecular mechanisms with axonal regeneration. However, whether IF influences the axonal regenerative ability remains to be investigated. Here we show that IF promotes axonal regeneration after sciatic nerve crush in the mouse via an unexpected mechanism that relies upon the gram + gut microbiome and an increase of the gut bacteria-derived metabolite indole-3-propionic acid (IPA) in the serum. IPA production by Clostridium sporogenes is required for efficient axonal regeneration, and delivery of IPA after sciatic injury significantly enhances axonal regeneration, accelerating recovery of sensory function. Mechanistically, RNA sequencing analysis from sciatic dorsal root ganglia suggested a role for neutrophil chemotaxis in the IPA-dependent regenerative phenotype that was confirmed by the inhibition of neutrophil chemotaxis. Our results demonstrate for the first time the ability of a microbiome derived metabolite, such as IPA, in facilitating regeneration and functional recovery of sensory axons via an immune-mediated mechanism. Since IPA is a naturally occurring metabolite with a very favourable toxicity profile, it represents a realistic translational possibility for human axonal injuries.

The regenerative potential of mammalian peripheral nervous system neurons after injury is critically limited by their slow axonal regenerative rate

RUNX1 is a transcription factor that plays key roles in haematopoietic development and in adult haematopoiesis and lymphopoiesis. Here we report that RUNX1 is also involved in controlling the dynamics of cell cycle entry of naïve resting B cells in response to stimulation of the B cell receptor (BCR). Conditional knockout ofRunx1in mouse resting B cells resulted in accelerated entry of the cells into S-phase following BCR engagement. Our results indicate that Runx1 regulates the cyclin D2 (Ccnd2) gene, the immediate early genes,Fosl2,Atf3andEgr2, and the Notch effectorRbpj, in B cells, reducing the rate at which transcription of these genes increases following BCR stimulation. RUNX1 interacts with the chromatin remodeller SRCAP, recruiting it to promoter and enhancer regions of theCcnd2gene. BCR-mediated activation triggers switching between binding of RUNX1 and its paralog RUNX3 and between SRCAP and the SWI/SNF remodelling complex member BRG1. We also find that RUNX1 regulates expression of a number of immunomodulatory genes in resting B cells. These include the interferon receptor subunit geneIfnar1, which is upregulated in B cells from lupus patients, thePtpn22gene, which has been identified as a major lupus risk allele, and theLrrk2gene, which is mutated in familial Parkinson’s disease. The hyperresponsiveness of theRunx1knockout B cells to antigen stimulation and its role in regulating a suite of genes that are known to be associated with autoimmune disease suggest that RUNX1 is a major regulator of B cell tolerance and autoimmunity.

Up to 20% of people worldwide develop gastrointestinal symptoms following a meal(1), leading to decreased quality of life, substantial morbidity and high medical costs. Although the interest of both the scientific and lay communities in this issue has increased markedly in recent years, with the worldwide introduction of gluten-free and other diets, the underlying mechanisms of food-induced abdominal complaints remain largely unknown. Here we show that a bacterial infection and bacterial toxins can trigger an immune response that leads to the production of dietary-antigen-specific IgE antibodies in mice, which are limited to the intestine. Following subsequent oral ingestion of the respective dietary antigen, an IgE- and mast-cell-dependent mechanism induced increased visceral pain. This aberrant pain signalling resulted from histamine receptor H-1-mediated sensitization of visceral afferents. Moreover, injection of food antigens (gluten, wheat, soy and milk) into the rectosigmoid mucosa of patients with irritable bowel syndrome induced local oedema and mast cell activation. Our results identify and characterize a peripheral mechanism that underlies food-induced abdominal pain, thereby creating new possibilities for the treatment of irritable bowel syndrome and related abdominal pain disorders. In mice, oral tolerance to food antigens can break down after enteric infection, and this leads to food-induced pain resembling irritable bowel syndrome in humans.

IgE is the least abundant circulating antibody class but is constitutively present in healthy tissues bound to resident cells via its high-affinity receptor, FcεRI. The physiological role of endogenous IgE is unclear but it is suggested to provide host protection against a variety of noxious environmental substances and parasitic infections at epithelial barrier surfaces. Here we show that skin inflammation enhances levels of IgE with natural specificities and with a similar repertoire, VDJ rearrangements and CDRH3 characteristics as in healthy tissue. IgE-bearing basophils are recruited to inflamed skin via CXCL12 and TSLP/IL-3-dependent upregulation of CXCR4. In the inflamed skin, IgE/FcεRI-signalling in basophils promotes epithelial cell growth and differentiation, partly through histamine engagement of H1R and H4R. Furthermore, this natural IgE response strongly drives tumour outgrowth of epithelial cells harbouring oncogenic mutation. These findings indicate that natural IgE support skin barrier defences however during chronic tissue inflammation this may be subverted to promote tumour growth.

IgE is the least abundant circulating antibody class but is constitutively present in healthy tissues bound to resident cells via its high-affinity receptor, FcεRI. The physiological role of endogenous IgE antibodies is unclear but it has been suggested that they provide host protection against a variety of noxious environmental substances and parasitic infections at epithelial barrier surfaces. Here we show, in mice, that skin inflammation enhances levels of IgE antibodies that have natural specificities and a repertoire, VDJ rearrangements and CDRH3 characteristics similar to those of IgE antibodies in healthy tissue. IgE-bearing basophils are recruited to inflamed skin via CXCL12 and thymic stromal lymphopoietin (TSLP)/IL-3-dependent upregulation of CXCR4. In the inflamed skin, IgE/FcεRI-signalling in basophils promotes epithelial cell growth and differentiation, partly through histamine engagement of H1R and H4R. Furthermore, this IgE response strongly drives tumour outgrowth of epithelial cells harbouring oncogenic mutation. These findings indicate that natural IgE antibodies support skin barrier defences, but that during chronic tissue inflammation this role may be subverted to promote tumour growth.

Embryo-derived Langerhans cells (eLC) are maintained within the sealed epidermis without contribution from circulating cells. When the network is perturbed by transient exposure to ultra-violet light, short-term LC are temporarily reconstituted from an initial wave of monocytes, but thought to be superseded by more permanent repopulation with undefined LC precursors. However, the extent to which this mechanism is relevant to immune-pathological processes that damage LC population integrity is not known. Using a model of allogeneic hematopoietic stem cell transplantation, where allo-reactive T cells directly target eLC, we have asked if and how the original LC network is ultimately restored. We find that donor monocytes, but not dendritic cells, are the precursors of the long-term LC in this context. Destruction of eLC leads to recruitment of a single wave of monocytes which engraft in the epidermis and undergo a sequential pathway of differentiation via transcriptionally distinct EpCAM+precursors. Monocyte-derived LC acquire the capacity of self-renewal, and turn-over in the epidermis was remarkably similar to that of steady state eLC. However, we have identified a bottleneck in the differentiation and survival of epidermal monocytes, which together with the slow turn-over of mature LC limits repair of the network. Furthermore, replenishment of the LC network leads to constitutive entry of cells into the epidermal compartment. Thus, immune injury triggers functional adaptation of mechanisms used to maintain tissue-resident macrophages at other sites, but this process is highly inefficient in the skin.HighlightsImmune injury leads to recruitment of a single wave of monocytes to replace resident Langerhans cells (LC).DC lineage cells cannot become long-term replacement LC.The size of the re-emerging network is controlled by density-dependent division of mature LC.Immune injury and inefficient repopulation by monocyte-derived cells lead to a permanently altered LC niche.

The mechanistic relationship between IL-4/IL-13 and skin barrier function has been of interest since the filaggrin discovery and the subsequent in vitro demonstration that IL-4 and IL-13 downregulate filaggrin expression in cultured keratinocytes. Hönzke and colleagues explore these interactions further. The effects of IL-4/ll-13 may be context dependent, with differing roles in homeostasis and in disease.

Background & Aims: Effective therapeutic approaches are urgently required to tackle the alarmingly poor survival outcomes in esophageal adenocarcinoma (EAC) patients. EAC originates from within the intestinal-type metaplasia, Barrett’s esophagus, a condition arising on a background of gastroesophageal reflux disease and associated inflammation. Methods: This study used a druggable genome small interfering RNA (siRNA) screening library of 6022 siRNAs in conjunction with bioinformatics platforms, genomic studies of EAC tissues, somatic variation data of EAC from The Cancer Genome Atlas data of EAC, and pathologic and functional studies to define novel EAC-associated, and targetable, immune factors. Results: By using a druggable genome library we defined genes that sustain EAC cell growth, which included an unexpected immunologic signature. Integrating Cancer Genome Atlas data with druggable siRNA targets showed a striking concordance and an EAC-specific gene amplification event associated with 7 druggable targets co-encoded at Chr6p21.1. Over-representation of immune pathway–associated genes supporting EAC cell growth included leukemia inhibitory factor, complement component 1, q subcomponent A chain (C1QA), and triggering receptor expressed on myeloid cells 2 (TREM2), which were validated further as targets sharing downstream signaling pathways through genomic and pathologic studies. Finally, targeting the triggering receptor expressed on myeloid cells 2-, C1q-, and leukemia inhibitory factor–activated signaling pathways (TYROBP–spleen tyrosine kinase and JAK-STAT3) with spleen tyrosine kinase and Janus-activated kinase inhibitor fostamatinib R788 triggered EAC cell death, growth arrest, and reduced tumor burden in NOD scid gamma mice. Conclusions: These data highlight a subset of genes co-identified through siRNA targeting and genomic studies of expression and somatic variation, specifically highlighting the contribution that immune-related factors play in support of EAC development and suggesting their suitability as targets in the treatment of EAC. Keywords: Esophageal Adenocarcinoma, Barrett’s Esophagus, Inflammation, Therapeutic Targets

The skin is under constant renewal and exposure to environmental challenges. How homeostasis is maintained alongside protective mechanisms against damage is unclear. Among the basal epithelial cells (ECs) is a population of resident intraepithelial lymphocytes (IELs) that provide host-protective immune surveillance. Here we show that IELs cross-communicate with ECs via the production of IL-13. Skin ECs are activated by IEL-derived IL-13, enabling a canonical EC stress response. In the absence of IL-13, or canonical IEL, the skin has decreased ability to repair its barrier and increased susceptibility to cutaneous carcinogenesis. IL-13 controls the rate of EC movement through the epidermis, which might explain the importance of IL-13 for epidermal integrity and its suppressive effect on skin carcinogenesis. These findings show that IL-13 acts as a molecular bridge between IELs and ECs, and reveal a critical host-defensive role for type-2 immunity in regulating EC tissue homeostasis and carcinogenesis., Epidermal intraepithelial lymphocytes (IEL) produce IL-13, but the physiological role of this cytokine production is not clear. Here the authors show that IEL-production of IL-13 is a vital lymphoid stress surveillance mechanism driving crosstalk with epithelial cells to maintain tissue homeostasis and inhibit chemical carcinogenesis in mice.

Epithelial cells respond to physicochemical damage with up-regulation of major histocompatibility complex-like ligands that can activate the cytolytic potential of neighboring intraepithelial T cells by binding the activating receptor, NKG2D. The systemic implications of this lymphoid stress-surveillance response, however, are unknown. We found that antigens encountered at the same time as cutaneous epithelial stress induced strong primary and secondary systemic, T helper 2 (T(H)2)-associated atopic responses in mice. These responses required NKG2D-dependent communication between dysregulated epithelial cells and tissue-associated lymphoid cells. These data are germane to uncertainty over the afferent induction of T(H)2 responses and provide a molecular framework for considering atopy as an important component of the response to tissue damage and carcinogenesis.

Summary Background. Children with atopic eczema (AE) are at risk of developing asthma. Airway inflammation has been shown to be present before the onset of clinical asthma. Increased exhalation (forced expiration; FE) of nitric oxide (FENO) and 8-isoprostane seems to be a feature of bronchial inflammation in people with asthma. Aim. To determine whether the exhalation of these two molecules is increased in children with eczema, even in the absence of overt asthma. Methods. In total, 21 children with AE were recruited and compared with healthy controls. A questionnaire was completed to identify respiratory symptoms compatible with asthma. The severity of AE was graded clinically. Spirometry, FENO measurements and exhaled breath condensate collection for 8-isoprostane were performed. Results. The mean level of 8-isoprostane was similar for children with AE (2.33 ± 4.76 pg/mL) and controls (3.37 ± 3.43). FENO was increased in children with AE (mean 64.97 parts per billion) compared with the normal range, even in the absence of respiratory symptoms and in the presence of normal lung function. Conclusions. FENO but not 8-isoprostane levels in exhaled breath condensate are higher in children with AE without asthma. Our finding may indicate a predictive role for FENO for the development of asthma.

Although studies of the skin have provided fundamental models for innate and adaptive immune surveillance of body surfaces, there remains relatively little understanding of the role that epithelial cells play in sensing infection and/or organ dysfunction, and the pathways available to them to communicate with local and systemic immune cells. In particular, evidence is emerging for a novel stress response initiated by local lymphocytes, rather than dendritic cells, and based on their recognition of epithelial stress-induced antigens. Its consequences are to sustain tissue integrity by providing immunoprotection and novel modes of immunoregulation, whereas its dysregulation may promote body surface immunopathologies.

Phagocytosis of microbial pathogens is essential for the host immune response to infection. Our previous work has shown that lipooligosaccharide (LOS) expression on the surface of Neisseria meningitidis (Nm) is essential for phagocytosis, but the receptor involved remained unclear. In this study, we show that human CR3 (CD11b/CD18) and CR4 (CD11c/CD18) are phagocytic receptors for Nm as illustrated by the capacity of CR3- and CR4-transfected Chinese hamster ovary (CHO) cells to facilitate Nm uptake. A CR3-signalling mutant failed to internalize Nm, showing that the ability of CR3 to signal is essential for phagocytosis. Internalization of Nm by CR3-transfected CHO cells could be inhibited by the presence of CR3-specific antibodies. Furthermore, dendritic cells from leukocyte adhesion deficiency-1 patients, who have diminished expression of beta2 integrins, showed markedly reduced phagocytosis of Nm. The CR3-mediated phagocytosis required the presence of lipopolysaccharide-binding protein (LBP). Furthermore, the expression of LOS by Nm was essential for LBP binding and phagocytosis via CR3. These results reveal a critical role of CR3 and LBP in the phagocytosis of Nm and provide important insights into the initial interaction meningococci have with the immune system.

Regulated migration and spatial localization of dendritic cells (DCs) are critical events during the initiation of physiologic immune responses and maintenance of tolerance. Here we have used cells deficient in the Wiskott-Aldrich syndrome protein (WASp) to demonstrate the importance of dynamic remodeling of the actin cytoskeleton for these trafficking processes to occur in vitro and in vivo. On fibronectin-coated surfaces, WASp-null immature murine DCs exhibited defects both of attachment and detachment, resulting in impaired net translocation compared with normal cells. The chemokinetic response to CCL21, which is critical for normal lymphatic trafficking, was also abrogated in the absence of WASp. In vivo in both fluorescein isothiocyanate (FITC) and oxazolone contact hypersensitivity models, WASp-null Langerhans cell (LC) migration was compromised, as judged by exit from the skin as well as by homing to the draining lymph node (LN). Furthermore, following systemic challenge with lipopolysaccharide (LPS) or toxoplasma-derived antigen, WASp-null DCs showed incomplete redistribution to T-cell areas in the spleen. Instead, they were retained ectopically in the marginal zone. DC trafficking in vivo is therefore dependent on a normally regulated actin cytoskeleton, which performs an essential function during maintenance of physiologic immunity and when disturbed may contribute significantly to the immunopathology of Wiskott-Aldrich Syndrome.

B cells constitute an essential line of defense from pathogenic infections through the generation of class-switched antibody-secreting cells (ASCs) in germinal centers. Although this process is known to be regulated by follicular helper T (TfH) cells, the mechanism by which B cells initially seed germinal center reactions remains elusive. We found that NKT cells, a population of innate-like T lymphocytes, are critical for the induction of B cell immunity upon viral infection. The positioning of NKT cells at the interfollicular areas of lymph nodes facilitates both their direct priming by resident macrophages and the localized delivery of innate signals to antigen-experienced B cells. Indeed, NKT cells secrete an early wave of IL-4 and constitute up to 70% of the total IL-4-producing cells during the initial stages of infection. Importantly, the requirement of this innate immunity arm appears to be evolutionarily conserved because early NKT and IL-4 gene signatures also positively correlate with the levels of neutralizing antibodies in Zika-virus-infected macaques. In conclusion, our data support a model wherein a pre-TfH wave of IL-4 secreted by interfollicular NKT cells triggers the seeding of germinal center cells and serves as an innate link between viral infection and B cell immunity. NKT cells are required for the initial formation of germinal centers and production of effective neutralizing antibody responses against viruses. Keywords: NKT cells; B cells; macrophages; germinal center seeding; IL-4; viral infection; influenza; Zika virus; lymph node; CXCR3

Background Short–term topical application of a Toll-like receptor 7 (TLR7) agonist, Imiquimod (IMQ), is a widely used murine model of psoriasis. Recently long–term epicutaneous application (4–8 weeks) of IMQ has been shown to elicit lupus-like manifestations. Importantly the topical application of IMQ induced more potent systemic effects than the intraperitoneal administration, indicating that activation of the TLR7-signalling in the skin plays a key role. Objectives Since complement activation is known to have a crucial role in the regulation of local inflammation and in the pathogenesis of lupus, we investigated whether C3 played a role in the induction of the cutaneous lesions as well as in the lupus-like syndrome triggered by IMQ Methods BALB/c wild-type (WT) and C3-deficient (BALB/c.C3 –/– ) mice were treated with topical application of 5% IMQ cream for either 7 consecutive days (short-term) or 3 days /week for 11 weeks (long-term). Results After 7 days, skin thickening (ear thickness at day 7: WT 60.14 mm ± 1.625, n=7, vs BALB/c.C3 –/– 50.88 mm ± 2.460, n=8, p value=0.0094) and local neutrophil recruitment (cell number at day 7: 52.3±6.736, n=7, vs BALB/c.C3 –/– 30.33±4.192, n=7, p value=0.0170) were significantly reduced in the absence of C3. The expansion of IL17 + γδ + T cells in the draining lymph nodes was also significantly impaired (day 7: WT 59.06% ± 2.961, n=7, vs BALB/c.C3 –/– 46.21% ± 2.023, n=8, p value=0.0029 ) . Long-term IMQ treatment resulted in the development of similar low titres of auto-antibodies in both groups of mice (anti-RNP: WT 29.75±11.33, n=5 vs BALB/c.C3 –/– 97.28±41.53, n=5, p=0.1553; anti-ssDNA: WT 9.252±3.367, n=5, vs BALB/c.C3 –/– 20.70±12.03, n=5, p=0.386; anti-chromatin: WT 12.59±7.001, n=5, vs BALB/c.C3 –/– 16.72±12.60, n=5, p=0.781). In addition, the kidney histology scored by a trained histopathologist evidenced no difference in the glomerulonephritis severity. Conclusions Collectively, these data suggest that C3 acts as a potential mediator of IMQ-induced skin inflammation. However, the different local tissue response does not result in an altered autoimmune response in the C3-deficient mice. The study of the involvement of other complement components is currently in progress. Disclosure of Interest None declared

The aim of the present systematic review was to evaluate the influence of early life exposure (maternal and childhood) to peanuts and the subsequent development of sensitisation or allergy to peanuts during childhood. Studies were identified using electronic databases and bibliography searches. Studies that assessed the impact of non-avoidance compared with avoidance or reduced quantities of peanuts or peanut products on either sensitisation or allergy to peanuts, or both outcomes, were eligible. Six human studies were identified: two randomised controlled trials, two case–control studies and two cross-sectional studies. In addition, published animal and mechanistic studies, relevant to the question of whether early life exposure to peanuts affects the subsequent development of peanut sensitisation, were reviewed narratively. Overall, the evidence reviewed was heterogeneous, and was limited in quality, for example, through lack of adjustment for potentially confounding factors. The nature of the evidence has therefore hindered the development of definitive conclusions. The systematic review of human studies and narrative expert-led reviews of animal studies do not provide clear evidence to suggest that either maternal exposure, or early or delayed introduction of peanuts in the diets of children, has an impact upon subsequent development of sensitisation or allergy to peanuts. Results from some animal studies (and limited evidence from human subjects) suggest that the dose of peanuts is an important mediator of peanut sensitisation and tolerance; low doses tend to lead to sensitisation and higher doses tend to lead to tolerance.

The self-encoded ligands MICA (human) and Rae-1 (mouse) for the cytotoxic lymphocyte activating receptor NKG2D are highly expressed in carcinomas and inflammatory lesions and have been linked to immunosurveillance and graft rejection. However, whether NKG2D ligands have an intrinsic ability to acutely regulate tissue-associated immune compartments is not known. Here we show that epidermis-specific upregulation of Rae-1 induced rapid, coincident and reversible changes in the organization of tissue-resident V(gamma)5V(delta)1 TCRgammadelta+ intraepithelial T cells and Langerhans cells, swiftly followed by epithelial infiltration by unconventional alphabeta T cells. Whereas local V(gamma)5V(delta)1+ T cells limited carcinogenesis, Langerhans cells unexpectedly promoted it. These results provide unique insight into the early phases of tissue immunosurveillance and indicate that acute changes in NKG2D ligands may alone initiate a rapid, multifaceted immunosurveillance response in vivo.

Background\ud Quantifying cell division and death is central to many studies in the biological sciences. The fluorescent dye CFSE allows the tracking of cell division in vitro and in vivo and provides a rich source of information with which to test models of cell kinetics. Cell division and death have a stochastic component at the single-cell level, and the probabilities of these occurring in any given time interval may also undergo systematic variation at a population level. This gives rise to heterogeneity in proliferating cell populations. Branching processes provide a natural means of describing this behaviour.\ud Results\ud We present a likelihood-based method for estimating the parameters of branching process models of cell kinetics using CFSE-labeling experiments, and demonstrate its validity using synthetic and experimental datasets. Performing inference and model comparison with real CFSE data presents some statistical problems and we suggest methods of dealing with them.\ud Conclusion\ud The approach we describe here can be used to recover the (potentially variable) division and death rates of any cell population for which division tracking information is available.

Epicutaneous immunization is a potential non-invasive technique for antigen-specific immune-modulation. Topical application of protein antigens to barrier-disrupted skin induces potent antigen-specific immunity with a strong Th2-bias. In this study, we investigate whether the autoimmune inflammatory response of chronic collagen-induced arthritis (CCIA) in DBA/1-TCR-beta Tg mice can be modified by epicutaneous immunization. We show that epicutaneous immunization with type II collagen (CII) inhibited development and progression of CCIA and, importantly, also ameliorated ongoing disease as indicated by clinical scores of disease severity, paw swelling and joints histology. Treated mice show reduced CII-driven T cell proliferation and IFN-gamma production, as well as significantly lower levels of CII-specific IgG2a serum antibodies. In contrast, CII-driven IL-4 production and IgE antibody levels were increased consistent with skewing of the CII response from Th1 to Th2 in treated mice. IL-4 production in treated mice was inversely correlated with disease severity. Moreover, T cells from treated mice inhibited proliferation and IFN-gamma production by T cells from CCIA mice, suggesting induction of regulatory T cells that actively inhibit effector responses in arthritic mice. The levels of CD4(+)CD25(+) T cells were however not increased following epicutaneous CII treatment. Together, these results suggest that epicutaneous immunization may be used as an immune-modulating procedure to actively re-programme pathogenic Th1 responses, and could have potential as a novel specific and simple treatment for chronic autoimmune inflammatory diseases such as rheumatoid arthritis.

Epicutaneous immunization is a potential novel technique for topical vaccine delivery. It targets the immunologically rich milieu of the skin while having the advantage of being a non-invasive immunization procedure. By disrupting the stratum corneum of the epidermis a natural adjuvant effect can be achieved through activation of resident Langerhans cells. This negates the normal need for co-application of noxious adjuvants. Epicutaneous immunization on barrier-disrupted skin induces potent antigen-specific systemic immunity with a strong T helper type 2 (Th2) bias. We show here that epicutaneous immunization enhances the vigour of a subsequent T-cell response to the same antigen. The induced systemic Th2 response prevents the development of Th1 responses induced through injection of antigen in complete Freund's adjuvant (CFA). Prior epicutaneous immunization results in reduced production of antigen-specific interferon-gamma and immunoglobulin G2a (IgG2a) and enhanced interleukin-4, IgG1 and IgE responses to immunization with CFA. Moreover, epicutaneous immunization converts an established Th1 response to a Th2 response, as demonstrated by the specific reduction of interferon-gamma and IgG2a and the enhancement of interleukin-4 and IgE. This Th2 dominance of epicutaneous immunization may have direct therapeutic application as an immune-modulating procedure in Th1-dominant diseases such as autoimmune rheumatoid arthritis, type 1 diabetes, Hashimoto's thyroiditis and multiple sclerosis.

Most allergic, atopic and hypersensitive reactions are associated with Th2-biased immune responses and allergen-specific IgE antibodies. Pathological allergic disorders are on an alarming increase in the industrialized world. Understanding the mechanism of primary sensitization to allergens is important in elucidating the pathogenesis of these diseases and for possibly preventing their development. In this article, we review recent information supporting that epidermal allergen exposure may contribute to systemic allergic diseases and that atopy may be secondary to skin barrier dysfunction in some dermatoses. The skin is an active immunological organ, which functions as a primary defence and biosensor to the external environment. The critical permeability barrier function is mediated by the outmost layer of the epidermis, the stratum corneum. Perturbation of the stratum corneum initiates a chain of event, which activates homeostatic responses in the underlying epidermis. Repeated barrier-disruption, whether environmentally or genetically determined, may however stimulate signaling cascades that lead to inflammation and epidermal hyperplasia. Skin barrier dysfunction may also allow entry of allergens, which can lead to primary systemic sensitization. The altered epidermal microenvironment in barrier-disrupted skin appears to be particularly well suited for the induction of potent Th2-type responses with production of allergen-specific IgE. Epidermal exposure to food antigens can prevent the normal induction of oral tolerance and also lead to airway eosinophilia following inhalation. Exposure to allergens on barrier-disrupted skin may as such serve as a natural sensitization pathway for food allergy and respiratory allergic disease.

The prevalence of food allergic diseases is rising and poses an increasing clinical problem. Peanut allergy affects around 1% of the population and is a common food allergy associated with severe clinical manifestations. The exact route of primary sensitization is unknown although the gastrointestinal immune system is likely to play an important role. Exposure of the gastrointestinal tract to soluble antigens normally leads to a state of antigen-specific systemic hyporesponsiveness (oral tolerance). A deviation from this process is thought to be responsible for food-allergic diseases. In this study, we have developed a murine model to investigate immunoregulatory processes after ingestion of peanut protein and compared this to a model of oral tolerance to chicken egg ovalbumin (OVA). We demonstrate that oral tolerance induction is highly dose dependent and differs for the allergenic proteins peanut and OVA. Tolerance to peanut requires a significantly higher oral dose than tolerance to OVA. Low doses of peanut are more likely to induce oral sensitization and increased production of interleukin-4 and specific immunoglobulin E upon challenge. When tolerance is induced both T helper 1 and 2 responses are suppressed. These results show that oral tolerance to peanut can be induced experimentally but that peanut proteins have a potent sensitizing effect. This model can now be used to define regulatory mechanisms following oral exposure to allergenic proteins on local, mucosal and systemic immunity and to investigate the immunomodulating effects of non-oral routes of allergen exposure on the development of allergic sensitization to peanut and other food allergens.

The skin is an important immunological organ with an outer protective layer, the stratum corneum forming a barrier between the skin-associated lymphoid tissue and the environment. We show that gently removing the stratum corneum with adhesive tape permits potent epicutaneous immunization to protein antigens. IL-4 secretion by T cells from draining lymph nodes and high levels of specific IgE and IgG1 with no IgG2a showed that the immune responses induced following epicutaneous antigen exposure are strongly Th2 biased. Similar responses were obtained with different antigens and mouse strains. In contrast, subcutaneous immunization with antigen delivery into the dermis was less potent and gave predominantly Th1 responses. Removal of the stratum corneum increased expression of MHC class II, CD86, CD40, CD54 and CD11c on Langerhans cells, but did not cause them to migrate. Rapid migration from epidermis to draining lymph node was obtained, however, by exposure to antigen after removal of the stratum corneum, suggesting that maturation and migration of Langerhans cells are independently regulated events. These results suggest that antigen presentation by Langerhans cells gives predominantly Th2 responses. This may provide an explanation for allergic sensitization to some antigens. It may also be a useful non-invasive, non-adjuvant-dependent method of vaccination.

The non-obese diabetic (NOD) mouse is a spontaneous animal model for type 1 diabetes characterized by a selective destruction of the insulin producing beta cells in the pancreas. As in humans, the disease is controlled by several susceptibility genes, some of which map to the major histocompatibility complex on chromosome 17. However, environmental factors also contribute to the development of the disease in the NOD mouse, presumably through controlling the balance between the Th1 and Th2 response in the animal. Recent observations have shown that the NOD mouse has abnormalities in the development of bone marrow-derived antigen-presenting cells. These include the most potent activators of naive T cells, the dendritic cells, which exist in at least two different sub-populations; DC1 cells, responsible for activation of Th1 cells, and DC2 cells, which produce Th2 cells. In addition to activating naive T cells, the dendritic cells are also involved in generating central and peripheral tolerance to self molecules. In this process DC2 cells appear to be more important for the development of peripheral tolerance than DC1 cells. Besides abnormalities in the development of bone marrow-derived antigen-presenting cells, the NOD mouse also has a defect in the thymic selection of T cells, leading to a higher concentration of autoreactive T cells. We speculate that the NOD mouse may develop an imbalance in the two subsets of dendritic cells with a skewing towards DC cells, thus having a reduced ability to generate peripheral tolerance to a number of autoantigens.

The non-obese diabetic (NOD) mouse is a spontaneous animal model for type 1 diabetes characterized by a selective destruction of the insulin producing beta cells in the pancreas. As in humans, the disease is controlled by several susceptibility genes, some of which map to the major histocompatibility complex on chromosome 17. However, environmental factors also contribute to the development of the disease in the NOD mouse, presumably through controlling the balance between the Th1 and Th2 response in the animal. Recent observations have shown that the NOD mouse has abnormalities in the development of bone marrow-derived antigen-presenting cells. These include the most potent activators of naive T cells, the dendritic cells, which exist in at least two different sub-populations; DC1 cells, responsible for activation of Th1 cells, and DC2 cells, which produce Th2 cells. In addition to activating naive T cells, the dendritic cells are also involved in generating central and peripheral tolerance to self molecules. In this process DC2 cells appear to be more important for the development of peripheral tolerance than DC1 cells. Besides abnormalities in the development of bone marrow-derived antigen-presenting cells, the NOD mouse also has a defect in the thymic selection of T cells, leading to a higher concentration of autoreactive T cells. We speculate that the NOD mouse may develop an imbalance in the two subsets of dendritic cells with a skewing towards DC cells, thus having a reduced ability to generate peripheral tolerance to a number of autoantigens.

Rationale The skin is an important immunological organ which is naturally exposed to a variety of environmental agents including allergens. The current study investigated the systemic effects of epicutaneous exposure to high molecular-weight proteins and allergens. Methods Ear skin of BALB/c mice was gently abraded with adhesive tape prior to application of peanut protein or ovalbumin. Immunity was investigated by studying specific T cell proliferation, cytokine secretion and immunoglobulin production. Epicutaneous immunization was compared to subcutaneous immunization. Skin immunity was explored by studying Langerhans cell (LC) maturation and migration. Results Abrasion of the skin allows potent epicutaneous immunization to protein antigens. High levels of antigen-specific IL-4, IgE and IgG1 with no IgG2a showed that the responses are strongly Th2 biased. Subcutaneous immunization was less potent and gave predominantly Th1 responses. Primary epicutaneous immunization changed responses elicited by subcutaneous antigen in complete Freunds adjuvant from Th1 to Th2. Additionally, epicutaneous immunization converted an existing antigen-specific Th1 response to a Th2 response, indicating dominance of the skin-induced immunity. Abrasion of the skin increased expression of MHC class II, CD86, CD40, CD54 and CD11c on LCs but did not cause migration. Rapid migration from epidermis to draining lymph node was observed only after skin abrasion and exposure to antigen, suggesting that maturation and migration of LCs are independently regulated events. Conclusions These results suggest that protein antigen presentation by LCs favors Th2 responses. This may provide an explanation for allergic sensitization to some antigens. It may also be a useful non-invasive, non-adjuvant-dependent method of vaccination.

Rationale Food allergies are a major cause of life-threatening hypersensitivity. Oral tolerance can be considered the default immune response to food antigens and disruption of this process may result in allergic sensitization. However, primary sensitization to food allergens may not be solely through the gastrointestinal mucosa, as strong Th2-biased immunity can be induced through cutaneous exposure to allergens. The purpose of this study was to determine whether exposure to allergens through the skin may interfere with oral tolerance and promote food allergies. Methods BALB/c mice were epicutaneously sensitized with peanut extract and induction of oral tolerance through single high dose feeds of peanut was subsequently assessed. Other mice were rendered tolerant prior to epicutaneous peanut exposure. Immune responses to peanut were determined by investigating DTH-, proliferative-, cytokine- and antibody responses. Results Epicutaneous exposure to peanut induced potent Th2-type immunity with high levels of IL-4 and IgE. Primary skin exposure prevented induction of oral tolerance to peanut. Upon oral challenge mice were further sensitized and developed strong peanut-specific IL-4 and IgE responses (p Conclusion Epicutaneous sensitization and oral challenge may be used as a physiologically relevant model for food-induced sensitisation without the need for adjuvants. Epicutaneous exposure to peanut allergens prevents induction of oral tolerance and even partially abrogates existing tolerance to peanut. This implies that skin exposure to allergens specifically drives Th2 responses and may as such promote food allergy upon gastrointestinal exposure.