Induction of regulatory T cells by a murine β-defensin

Beta-defensin index: A functional biomarker for oral cancer detection

There is an unmet clinical need for a non-invasive and cost-effective test for oral squamous cell carcinoma (OSCC) that informs clinicians when a biopsy is warranted. Human beta-defensin 3 (hBD-3), an epithelial cell-derived anti-microbial peptide, is pro-tumorigenic and overexpressed in early-stage OSCC compared to hBD-2. We validate this expression dichotomy in carcinoma in situ and OSCC lesions using immunofluorescence microscopy and flow cytometry. The proportion of hBD-3/hBD-2 levels in non-invasively collected lesional cells compared to contralateral normal cells, obtained by ELISA, generates the beta-defensin index (BDI). Proof-of-principle and blinded discovery studies demonstrate that BDI discriminates OSCC from benign lesions. A multi-center validation study shows sensitivity and specificity values of 98.2% (95% confidence interval [CI] 90.3-99.9) and 82.6% (95% CI 68.6-92.2), respectively. A proof-of-principle study shows that BDI is adaptable to a point-of-care assay using microfluidics. We propose that BDI may fulfill a major unmet need in low-socioeconomic countries where pathology services are lacking.

Defensins: A novel weapon against Mycobacterium tuberculosis?

Tuberculosis (TB) is a serious airborne communicable disease caused by organisms of the Mycobacterium tuberculosis (Mtb) complex. Although the standard treatment antimicrobials, including isoniazid, rifampicin, pyrazinamide, and ethambutol, have made great progress in the treatment of TB, problems including the rising incidence of multidrug-resistant tuberculosis (MDR-TB) and extensively drug-resistant tuberculosis (XDR-TB), the severe toxicity and side effects of antimicrobials, and the low immunity of TB patients have become the bottlenecks of the current TB treatments. Therefore, both safe and effective new strategies to prevent and treat TB have become a top priority. As a subfamily of cationic antimicrobial peptides, defensins are rich in cysteine and play a vital role in resisting the invasion of microorganisms and regulating the immune response. Inspired by studies on the roles of defensins in host defence, we describe their research history and then review their structural features and antimicrobial mechanisms, specifically for fighting Mtb in detail. Finally, we discuss the clinical relevance, therapeutic potential, and potential challenges of defensins in anti-TB therapy. We further debate the possible solutions of the current application of defensins to provide new insights for eliminating Mtb.

Human β-defensin 2 ameliorates acute GVHD by limiting ileal neutrophil infiltration and restraining T cell receptor signaling

Acute graft-versus-host disease (aGVHD), which is driven by allogeneic T cells, has a high mortality rate and limited treatment options. Human β-defensin 2 (hBD-2) is an endogenous epithelial cell-derived host-defense peptide. In addition to its antimicrobial effects, hBD-2 has immunomodulatory functions thought to be mediated by CCR2 and CCR6 in myeloid cells. In this study, we analyzed the effect of recombinant hBD-2 on aGVHD development. We found that intestinal β-defensin expression was inadequately induced in response to inflammation in two independent cohorts of patients with aGVHD and in a murine aGVHD model. Treatment of mice with hBD-2 reduced GVHD severity and mortality and modulated the intestinal microbiota composition, resulting in reduced neutrophil infiltration in the ileum. Furthermore, hBD-2 treatment decreased proliferation and proinflammatory cytokine production by allogeneic T cells in vivo while preserving the beneficial graft-versus-leukemia effect. Using transcriptome and kinome profiling, we found that hBD-2 directly dampened primary murine and human allogeneic T cell proliferation, activation, and metabolism in a CCR2- and CCR6-independent manner by reducing proximal T cell receptor signaling. Furthermore, hBD-2 treatment diminished alloreactive T cell infiltration and the expression of genes involved in T cell receptor signaling in the ilea of mice with aGVHD. Together, we found that both human and murine aGVHD were characterized by a lack of intestinal β-defensin induction and that recombinant hBD-2 represents a potential therapeutic strategy to counterbalance endogenous hBD-2 deficiency.

Keratinocyte-derived defensins activate neutrophil-specific receptors Mrgpra2a/b to prevent skin dysbiosis and bacterial infection

Healthy skin maintains a diverse microbiome and a potent immune system to fight off infections. Here, we discovered that the epithelial-cell-derived antimicrobial peptides defensins activated orphan G-protein-coupled receptors (GPCRs) Mrgpra2a/b on neutrophils. This signaling axis was required for effective neutrophil-mediated skin immunity and microbiome homeostasis. We generated mutant mouse lines lacking the entire Defensin (Def) gene cluster in keratinocytes or Mrgpra2a/b. Def and Mrgpra2 mutant animals both exhibited skin dysbiosis, with reduced microbial diversity and expansion of Staphylococcus species. Defensins and Mrgpra2 were critical for combating S. aureus infections and the formation of neutrophil abscesses, a hallmark of antibacterial immunity. Activation of Mrgpra2 by defensin triggered neutrophil release of IL-1β and CXCL2 which are vital for proper amplification and propagation of the antibacterial immune response. This study demonstrated the importance of epithelial-neutrophil signaling via the defensin-Mrgpra2 axis in maintaining healthy skin ecology and promoting antibacterial host defense.

Expression of antimicrobial host defence peptides in the central nervous system during health and disease

Antimicrobial host defence peptides (HDP) are critical for the first line of defence against bacterial, viral, and fungal pathogens. Over the past decade we have become more aware that, in addition to their antimicrobial roles, they also possess the potent immunomodulatory capacity. This includes chemoattracting immune cells, activating dendritic cells and macrophages, and altering T-cell differentiation. Most examinations of their immunomodulatory roles have focused on tissues in which they are very abundant, such as the intestine and the inflamed skin. However, HDP have now been detected in the brain and the spinal cord during a number of conditions. We propose that their presence in the central nervous system (CNS) during homeostasis, infection, and neurodegenerative disease has the potential to contribute to immunosurveillance, alter host responses and skew developing immunity. Here, we review the evidence for HDP expression and function in the CNS in health and disease. We describe how a wide range of HDP are expressed in the CNS of humans, rodents, birds, and fish, suggesting a conserved role in protecting the brain from pathogens, with evidence of production by resident CNS cells. We highlight differences in methodology used and how this may have resulted in the immunomodulatory roles of HDP being overlooked. Finally, we discuss what HDP expression may mean for CNS immune responses.

Controllers of cutaneous regulatory T cells: ultraviolet radiation and the skin microbiome

For the maintenance of homeostasis termination of immune reactions is as equally important as their induction. In this scenario regulatory T cells (Treg) play an important role. Accordingly a variety of inflammatory diseases are caused by an impairment of Treg. Hence, it is important to identify triggers by which Treg can be induced and activated, respectively. For quite a long time it is known that ultraviolet radiation can induce Treg which inhibit cutaneous immune reactions including contact hypersensitivity. Since these Treg inhibit in an antigen-specific fashion they may harbor therapeutic potential. However similar Treg can be induced also by other triggers which include vitamin D and antimicrobial peptides. Recently it was discovered that the gut microbiome controls the development of Treg in the intestine. The same may apply for the skin. Short chain fatty acids, microbiota-derived bacterial fermentation products, appear to induce and to activate Treg in the skin. Topical application of short chain fatty acids was shown to inhibit contact hypersensitivity and to reduce inflammation in the murine imiquimod-induced psoriasis-like skin inflammation model. Together, these data indicate that induction and activation of Treg may be a potential therapeutic strategy to treat inflammatory diseases in the future.

Dissecting the relationship between antimicrobial peptides and mesenchymal stem cells

Among the various biological properties presented by Mesenchymal Stem Cells (MSCs), their ability to control the immune response and fight pathogen infection through the production of antimicrobial peptides (AMPs) have been the subject of intense research in recent years. AMPs secreted by MSCs exhibit activity against a wide range of microorganisms, including bacteria, fungi, yeasts, and viruses. The main AMPs produced by these cells are hepcidin, cathelicidin LL-37, and β-defensin-2. In addition to acting against pathogens, those AMPs have also been shown to interact with MSCs to modulate MSC proliferation, migration, and regeneration, indicating that such peptides exert a more diverse biological effect than initially thought. In the present review, we discuss the production of AMPs by MSCs, revise the multiple functions of these peptides, including their influence over MSCs, and present an overview of clinical situations in which the antimicrobial properties of MSCs may be explored for therapy. Finally, we discuss possibilities of combining MSCs and AMPs to generate improved therapeutic strategies.

Butyrate as a bioactive human milk protective component against food allergy

BACKGROUND

Food allergy (FA) is a growing health problem worldwide. Effective strategies are advocated to limit the disease burden. Human milk (HM) could be considered as a protective factor against FA, but its mechanisms remain unclear. Butyrate is a gut microbiota-derived metabolite able to exert several immunomodulatory functions. We aimed to define the butyrate concentration in HM, and to see whether the butyrate concentration detected in HM is able to modulate the mechanisms of immune tolerance.

METHODS

HM butyrate concentration from 109 healthy women was assessed by GS-MS. The effect of HM butyrate on tolerogenic mechanisms was assessed in in vivo and in vitro models.

RESULTS

The median butyrate concentration in mature HM was 0.75 mM. This butyrate concentration was responsible for the maximum modulatory effects observed in all experimental models evaluated in this study. Data from mouse model show that in basal condition, butyrate up-regulated the expression of several biomarkers of gut barrier integrity, and of tolerogenic cytokines. Pretreatment with butyrate significantly reduced allergic response in three animal models of FA, with a stimulation of tolerogenic cytokines, inhibition of Th2 cytokines production and a modulation of oxidative stress. Data from human cell models show that butyrate stimulated human beta defensin-3, mucus components and tight junctions expression in human enterocytes, and IL-10, IFN-γ and FoxP3 expression through epigenetic mechanisms in PBMCs from FA children. Furthermore, it promoted the precursors of M2 macrophages, DCs and regulatory T cells.

CONCLUSION

The study's findings suggest the importance of butyrate as a pivotal HM compound able to protect against FA.

The Dual Role of Antimicrobial Peptides in Autoimmunity

Autoimmune diseases (AiDs) are characterized by the destruction of host tissues by the host immune system. The etiology of AiDs is complex, with the implication of multiple genetic defects and various environmental factors (pathogens, antibiotic use, pollutants, stress, and diet). The interaction between these two compartments results in the rupture of tolerance against self-antigens and the unwanted activation of the immune system. Thanks to animal models, the immunopathology of many AiDs is well described, with the implication of both the innate and adaptive immune systems. This progress toward the understanding of AiDs led to several therapies tested in patients. However, the results from these clinical trials have not been satisfactory, from reversing the course of AiDs to preventing them. The need for a cure has prompted many investigators to explore alternative aspects in the immunopathology of these diseases. Among these new aspects, the role of antimicrobial host defense peptides (AMPs) is growing. Indeed, beyond their antimicrobial activity, AMPs are potent immunomodulatory molecules and consequently are implicated in the development of numerous AiDs. Importantly, according to the disease considered, AMPs appear to play a dual role in autoimmunity with either anti- or pro-inflammatory abilities. Here, we aimed to summarize the current knowledge about the role of AMPs in the development of AiDs and attempt to provide some hypotheses explaining their dual role. Definitely, a complete understanding of this aspect is mandatory before the design of AMP-based therapies against AiDs.

The Dichotomous Responses Driven by β-Defensins

Defensins are short, rapidly evolving, cationic antimicrobial host defence peptides with a repertoire of functions, still incompletely realised, that extends beyond direct microbial killing. They are released or secreted at epithelial surfaces, and in some cases, from immune cells in response to infection and inflammation. Defensins have been described as endogenous alarmins, alerting the body to danger and responding to inflammatory signals by promoting both local innate and adaptive systemic immune responses. However, there is now increasing evidence that they exert variable control on the response to danger; creating a dichotomous response that can suppress inflammation in some circumstances but exacerbate the response to danger and damage in others and, at higher levels, lead to a cytotoxic effect. Focussing in this review on human β-defensins, we discuss the evidence for their functions as proinflammatory, immune activators amplifying the response to infection or damage signals and/or as mediators of resolution of damage, contributing to a return to homeostasis. Finally, we consider their involvement in the development of autoimmune diseases.

Mechanisms of TREG cell adaptation to inflammation

Inflammation is an important defense mechanism. In this complex and dynamic process, drastic changes in the tissue micro-environment play key roles in dictating the nature of the evolving immune response. However, uncontrolled inflammation is detrimental, leading to unwanted cellular damage, loss of physiological functions, and even death. As such, the immune system possesses tools to limit inflammation while ensuring rapid and effective clearance of the inflammatory trigger. Foxp3⁺ regulatory T (T_REG ) cells, a potently immunosuppressive CD4⁺ T cell subset, play a crucial role in immune tolerance by controlling the extent of the response to self and non-self Ags, all-the-while promoting a quick return to immune homeostasis. T_REG cells adapt to changes in the local micro-environment enabling them to migrate, proliferate, survive, differentiate, and tailor their suppressive ability at inflamed sites. Several inflammation-associated factors can impact T_REG cell functional adaptation in situ including locally released alarmins, oxygen availability, tissue acidity and osmolarity and nutrient availability. Here, we review some of these key signals and pathways that control the adaptation of T_REG cell function in inflammatory settings.

[Psoriasis and the microbiome]

BACKGROUND

Psoriasis is a frequent chronic inflammatory systemic disease. It is associated with changes in the microbiome, which may trigger psoriasis and influence the course of the disease.

OBJECTIVE

Current methods for detection and the potential role of the microbiome in the pathogenesis of psoriasis are described.

MATERIAL AND METHODS

A literature search was conducted using the databases Medline and PubMed as well as a general internet and book research.

RESULTS

Both skin and gut microbiota are involved in the immunopathogenesis and may substantially modulate psoriasis. Antimicrobial peptides may serve as a link between the microbiome and the immunological mechanisms in psoriasis by regulating the microbiome at interfaces and can trigger psoriasis as antigens. Recent innovative methods, such as 16S rRNA next-generation sequencing significantly facilitate microbiome analysis.

CONCLUSION

The analysis of the microbiome in patients with psoriasis before, during and after treatment provides a basis for the identification of potential biomarkers for predicting individual treatment responses and facilitating the decision for a certain treatment.

Gut Microbiota-Stimulated Innate Lymphoid Cells Support β-Defensin 14 Expression in Pancreatic Endocrine Cells, Preventing Autoimmune Diabetes

The gut microbiota is essential for the normal function of the gut immune system, and microbiota alterations are associated with autoimmune disorders. However, how the gut microbiota prevents autoimmunity in distant organs remains poorly defined. Here we reveal that gut microbiota conditioned innate lymphoid cells (ILCs) induce the expression of mouse β-defensin 14 (mBD14) by pancreatic endocrine cells, preventing autoimmune diabetes in the non-obese diabetic (NOD) mice. MBD14 stimulates, via Toll-like receptor 2, interleukin-4 (IL-4)-secreting B cells that induce regulatory macrophages, which in turn induce protective regulatory T cells. The gut microbiota-derived molecules, aryl hydrocarbon receptor (AHR) ligands and butyrate, promote IL-22 secretion by pancreatic ILCs, which induce expression of mBD14 by endocrine cells. Dysbiotic microbiota and low-affinity AHR allele explain the defective pancreatic expression of mBD14 observed in NOD mice. Our study reveals a yet unidentified crosstalk between ILCs and endocrine cells in the pancreas that is essential for the prevention of autoimmune diabetes development.

Characterization of the β-defensin genes in giant panda

β-Defensins are small antimicrobial proteins expressed in various organisms and have great potential for improving animal health and selective breeding programs. Giant pandas have a distinctive lineage in Carnivora, and it is unclear whether β-defensin genes have experienced different selective pressures during giant panda evolution. We therefore characterized the giant panda (Ailuropoda melanoleuca) β-defensin gene family through gap filling, TBLASTN, and HMM searches. Among 36 β-defensins identified, gastrointestinal disease may induce the expression of the DEFB1 and DEFB139 genes in the digestive system. Moreover, for DEFB139, a significant positive selection different from that of its homologs was revealed through branch model comparisons. A Pro-to-Arg mutation in the giant panda DEFB139 mature peptide may have enhanced the peptide’s antimicrobial potency by increasing its stability, isoelectric point, surface charge and surface hydrophobicity, and by stabilizing its second β-sheet. Broth microdilution tests showed that the increase in net charge caused by the Pro-to-Arg mutation has enhanced the peptide’s potency against Staphylococcus aureus, although the increase was minor. We expect that additional gene function and expression studies of the giant panda DEFB139 gene could improve the existing conservation strategies for the giant panda.

Reciprocal role of hBD2 and hBD3 on the adaptive immune response by measuring T lymphocyte proliferation in terms of CD4 and CCR6 expression

Background Human β-defensins (hBD2 and hBD3) are small cationic antimicrobial peptides of innate immune system which can act as a barrier against the majority of pathogens, contributing to the host immune defence. Objective The aim of study is to determine whether hBD2 and hBD3 play a role in development and proliferation of human effector CD4 T cells or not. Furthermore, if enhanced proliferation is observed in the presence of hBD2 and hBD3, these data will demonstrate whether chemokine receptor type 6 (CCR6) is required to be present for this activity to occur. Methods In this study, we examined the effect of hBD2 and hBD3 on CD4+ T cell proliferation in CCR6+ and CCR6- T cells through co-culture of peripheral blood mononuclear cells with anti-CD3 and anti-CD28 stimulation in the presence or absence of hBD2 and hBD3. Proliferation was assessed using flow cytometry. Results It was demonstrated that, co-culture with hBD2 and hBD3 led to up-regulation of CD4+ T cell proliferation after 72 h whereas, CD4+ T cell proliferation was suppressed after 96 h. On the other hand, CCR6- and CCR6+ T cell proliferation was up-regulated after 72 h. But, CCR6+ only was down-regulated in the second cycle in the presence of hBD3. In contrast, after 96 h CCR6+ and CCR6- T cell proliferation was decreased. Conclusion Collectively, our data indicated that hBD2 and hBD3 play a positive and negative regulatory role in development and proliferation of human effector CD4+ T cells which is essential for optimal adaptive immune responses and the control of immunopathology.

The role of UV radiation and vitamin D in the seasonality and outcomes of infectious disease

The seasonality of infectious disease outbreaks suggests that environmental conditions have a significant effect on disease risk. One of the major environmental factors that can affect this is solar radiation, primarily acting through ultraviolet radiation (UVR), and its subsequent control of vitamin D production. Here we show how UVR and vitamin D, which are modified by latitude and season, can affect host and pathogen fitness and relate them to the outcomes of bacterial, viral and vector-borne infections. We conducted a thorough comparison of the molecular and cellular mechanisms of action of UVR and vitamin D on pathogen fitness and host immunity and related these to the effects observed in animal models and clinical trials to understand their independent and complementary effects on infectious disease outcome. UVR and vitamin D share common pathways of innate immune activation primarily via antimicrobial peptide production, and adaptive immune suppression. Whilst UVR can induce vitamin D-independent effects in the skin, such as the generation of photoproducts activating interferon signaling, vitamin D has a larger systemic effect due to its autocrine and paracrine modulation of cellular responses in a range of tissues. However, the seasonal patterns in infectious disease prevalence are not solely driven by variation in UVR and vitamin D levels across latitudes. Vector-borne pathogens show a strong seasonality of infection correlated to climatic conditions favoring their replication. Conversely, pathogens, such as influenza A virus, Mycobacterium tuberculosis and human immunodeficiency virus type 1, have strong evidence to support their interaction with vitamin D. Thus, UVR has both vitamin D-dependent and independent effects on infectious diseases; these effects vary depending on the pathogen of interest and the effects can be complementary or antagonistic.

A Perspective on the Interplay of Ultraviolet-Radiation, Skin Microbiome and Skin Resident Memory TCRαβ+ Cells

The human skin is known to be inhabited by diverse microbes, including bacteria, fungi, viruses, archaea, and mites. This microbiome exerts a protective role against infections by promoting immune development and inhibiting pathogenic microbes to colonize skin. One of the factors having an intense effect on the skin and its resident microbes is ultraviolet-radiation (UV-R). UV-R can promote or inhibit the growth of microbes on the skin and modulate the immune system which can be either favorable or harmful. Among potential UV-R targets, skin resident memory T cells (T_RM) stand as well positioned immune cells at the forefront within the skin. Both CD4⁺ or CD8⁺ αβ T_RM cells residing permanently in peripheral tissues have been shown to play prominent roles in providing accelerated and long-lived specific immunity, tissue homeostasis, wound repair. Nevertheless, their response upon UV-R exposure or signals from microbiome are poorly understood compared to resident TCRγδ cells. Skin T_RM survive for long periods of time and are exposed to innumerable antigens during lifetime. The interplay of T_RM with skin residing microbes may be crucial in pathophysiology of various diseases including psoriasis, atopic dermatitis and polymorphic light eruption. In this article, we share our perspective about how UV-R may directly shape the persistence, phenotype, specificity, and function of skin T_RM; and moreover, whether UV-R alters barrier function, leading to microbial-specific skin T_RM, disrupting the healthy balance between skin microbiome and skin immune cells, and resulting in chronic inflammation and diseased skin.

Microbial Host Interactions and Impaired Wound Healing in Mice and Humans: Defining a Role for BD14 and NOD2

Chronic wounds cause significant patient morbidity and mortality. A key factor in their etiology is microbial infection, yet skin host-microbiota interactions during wound repair remain poorly understood. Microbiome profiles of noninfected human chronic wounds are associated with subsequent healing outcome. Furthermore, poor clinical healing outcome was associated with increased local expression of the pattern recognition receptor NOD2. To investigate NOD2 function in the context of cutaneous healing, we treated mice with the NOD2 ligand muramyl dipeptide and analyzed wound repair parameters and expression of antimicrobial peptides. Muramyl dipeptide treatment of littermate controls significantly delayed wound repair associated with reduced re-epithelialization, heightened inflammation, and up-regulation of murine β-defensins 1, 3, and particularly 14. We postulated that although murine β-defensin 14 might affect local skin microbial communities, it may further affect other healing parameters. Indeed, exogenously administered murine β-defensin 14 directly delayed mouse primary keratinocyte scratch wound closure in vitro. To further explore the role of murine β-defensin 14 in wound repair, we used Defb14^-/- mice and showed they had a global delay in healing in vivo, associated with alterations in wound microbiota. Taken together, these studies suggest a key role for NOD2-mediated regulation of local skin microbiota, which in turn affects chronic wound etiology.

Mouse β-defensin-14 for inducing the maturation of dendritic cells

BACKGROUND

β-defensins are an excellent antimicrobial peptide against microbial infection in which dendritic cells (DCs) play a crucial role by improving the innate and adaptive immune defense. However, it is unclear whether BDs affect DC maturation. This work aimed to study the effects of mouse β-defensin-14 (MBD-14) on DC maturation.

METHODS

Via in vitro using mouse bone marrow DCs, the maturation of DCs was evaluated by cell morphological staining, flow cytometry, endocytosis assay, and allogeneic mixed lymphocyte reaction, respectively. And it was also assessed by in vivo establishing a mouse air-pouch model for flow cytometric determination, cytokine analysis, and histological staining. Additionally, CLI-095, an inhibitor of Toll-like receptor-4 (TLR-4), was used to determine whether TLR-4 is possibly involved in DC maturation.

RESULTS

It was found MBD-14 promoted DCs to form more filopodia and lamellipodia, increased the expression of DC maturation markers (CD40 and MHC-II), decreased their endocytic capacity, and enhanced T-cell proliferation. The analyses of the air-pouch exudates were consistent with the in vitro results of MBD-14 activating DCs. And when CLI-095 was applied, DC maturation was inhibited partly.

CONCLUSIONS

This work demonstrates that MBD-14 can promote the maturation of DCs in which TLR-4 is possibly involved.

Unique profile of antimicrobial peptide expression in polymorphic light eruption lesions compared to healthy skin, atopic dermatitis, and psoriasis

Background

Polymorphic light eruption (PLE) has been attributed to type IV, most likely delayed‐type hypersensitivity response (adaptive immunity) but little is known on innate immunity, especially antimicrobial peptides (AMPs) in the disease. Abnormalities in AMP expression have been linked to pathological skin conditions such as atopic dermatitis (AD) and psoriasis.

Methods

Antimicrobial peptide profiling was carried out in PLE skin samples (n,12) compared with that of healthy (n,13), atopic (n,6), and psoriatic skin (n,6).

Results

Compared to healthy skin, we observed increased expression of psoriasin and RNAse7 (both mostly in stratum granulosum of the epidermis), HBD‐2 (in the cellular infiltrate of the dermis), and LL37 (mostly in and around blood vessels and glands) in PLE lesional skin, a similar expression profile as present in psoriatic skin and different to that of AD (with little or no expression of psoriasin, RNAse7, HBD‐2, and LL37). HBD‐3 was downregulated in PLE compared to its high expression in the epidermis and dermis of healthy skin, AD, and psoriasis.

Conclusion

The unique profile of differentially expressed AMPs in PLE implies a role in the pathophysiology of the disease, possibly directly or indirectly linked to the microbiome of the skin.

Disruption of the Epidermal Barrier Induces Regulatory T Cells via IL-33 in Mice

Disturbance of the epidermal barrier by UVR is associated with the release of antimicrobial peptides and inflammatory cytokines for the purpose of a danger response. On the other hand, UVR causes immunosuppression via regulatory T cells (Treg) that limit the inflammatory reaction. The concurrent induction of antimicrobial peptides and Treg by UVR may represent a counter-regulatory mechanism in response to barrier disruption, preventing microbial superinfection and sensitization to contact allergens, respectively, both of which cross impaired epidermis more easily. Thus, using a model of murine contact hypersensitivity we examined if disruption of the epidermal barrier only initiates similar counter-regulatory mechanisms via the generation of Treg. Sensitization through tape-stripped skin induced a weaker contact hypersensitivity response than in control mice. This was due to the induction of antigen-specific Treg, as demonstrated in adoptive transfer and depletion experiments utilizing DEREG mice. Treg induction by tape stripping was linked to the expression of the alarmin IL-33, as blockade of IL-33 exacerbated contact hypersensitivity, whereas injection of IL-33 inhibited contact hypersensitivity and induced Treg. These results demonstrate that epidermal barrier disruption, in addition to danger signals, induces regulatory events that prevent exaggerated skin inflammation and that IL-33 appears to be critically involved in this process.

β-defensins and the epididymis: contrasting influences of prenatal, postnatal, and adult scenarios

β-defensins are components of host defense, with antimicrobial and pleiotropic immuno-modulatory properties. Research over the last 15 years has demonstrated abundant expression of a variety of β-defensins in the postnatal epididymis of different species. A gradient of region- and cell-specific expression of these proteins is observed in the epithelium of the postnatal epididymis. Their secretion into the luminal fluid and binding to spermatozoa as they travel along the epididymis has suggested their involvement in reproduction-specific tasks. Therefore, continuous attention has been given to various β-defensins for their role in sperm function and fertility. Although β-defensins are largely dependent on androgens, the underlying mechanisms regulating their expression and function in the epididymis are not well understood. Recent investigation has pointed out to a new and interesting scenario where β-defensins emerge with a different expression pattern in the Wolffian duct, the embryonic precursor of the epididymis, as opposed to the adult epididymis, thereby redefining the concept concerning the multifunctional roles of β-defensins in the developing epididymis. In this review, we summarize some current views of β-defensins in the epididymis highlighting our most recent data and speculations on their role in the developing epididymis during the prenatal-to-postnatal transition, bringing attention to the many unanswered questions in this research area that may contribute to a better understanding of epididymal biology and male fertility.

The Skin Microbiome: Is It Affected by UV-induced Immune Suppression?

Human skin apart from functioning as a physical barricade to stop the entry of pathogens, also hosts innumerable commensal organisms. The skin cells and the immune system constantly interact with microbes, to maintain cutaneous homeostasis, despite the challenges offered by various environmental factors. A major environmental factor affecting the skin is ultraviolet radiation (UV-R) from sunlight. UV-R is well known to modulate the immune system, which can be both beneficial and deleterious. By targeting the cells and molecules within skin, UV-R can trigger the production and release of antimicrobial peptides, affect the innate immune system and ultimately suppress the adaptive cellular immune response. This can contribute to skin carcinogenesis and the promotion of infectious agents such as herpes simplex virus and possibly others. On the other hand, a UV-established immunosuppressive environment may protect against the induction of immunologically mediated skin diseases including some of photodermatoses such as polymorphic light eruption. In this article, we share our perspective about the possibility that UV-induced immune suppression may alter the landscape of the skin’s microbiome and its components. Alternatively, or in concert with this, direct UV-induced DNA and membrane damage to the microbiome may result in pathogen associated molecular patterns (PAMPs) that interfere with UV-induced immune suppression.

Prevention and Mitigation of Experimental Autoimmune Encephalomyelitis by Murine β-Defensins via Induction of Regulatory T Cells

The antimicrobial peptide murine β-defensin-14 (mBD14) was found to exert, in addition to its antimicrobial activity, the capacity to induce regulatory T cells as demonstrated in the model of contact hypersensitivity. Because it is induced by ultraviolet radiation, mBD14 may contribute to the antigen-specific immunosuppression by ultraviolet radiation. To prove whether this applies also for other immunologic models and because ultraviolet radiation appears to have beneficial effects on multiple sclerosis, we utilized the model of experimental autoimmune encephalomyelitis. Injection of mBD14 into mice before immunization with myelin oligodendrocyte glycoprotein caused amelioration of the disease with less central nervous system inflammation and decreased levels of proinflammatory cytokines and cytotoxic T cells. The beneficial effect was due to Foxp3(+) regulatory T cells because it was lost on in vivo depletion of regulatory T cells. mBD14, however, also acts in a therapeutic setting, because injection of mBD14 into mice with clinical features of experimental autoimmune encephalomyelitis reduced the clinical score significantly. Human β-defensin-3, the human orthologue of mBD14, induced in vitro regulatory T cell-specific markers in CD4(+)CD25(-) T cells, shifting these nonregulatory cells into a regulatory phenotype with suppressive features. Thus, defensins may represent candidates worth being further pursued for the therapy of multiple sclerosis.

Amplifying renal immunity: the role of antimicrobial peptides in pyelonephritis

Urinary tract infections (UTIs), including pyelonephritis, are among the most common and serious infections encountered in nephrology practice. UTI risk is increased in selected patient populations with renal and urinary tract disorders. As the prevalence of antibiotic-resistant uropathogens increases, novel and alternative treatment options will be needed to reduce UTI-associated morbidity. Discoveries over the past decade demonstrate a fundamental role for the innate immune system in protecting the urothelium from bacterial challenge. Antimicrobial peptides, an integral component of this urothelial innate immune system, demonstrate potent bactericidal activity toward uropathogens and might represent a novel class of UTI therapeutics. The urothelium of the bladder and the renal epithelium secrete antimicrobial peptides into the urinary stream. In the kidney, intercalated cells--a cell-type involved in acid-base homeostasis--have been shown to be an important source of antimicrobial peptides. Intercalated cells have therefore become the focus of new investigations to explore their function during pyelonephritis and their role in maintaining urinary tract sterility. This Review provides an overview of UTI pathogenesis in the upper and lower urinary tract. We describe the role of intercalated cells and the innate immune response in preventing UTI, specifically highlighting the role of antimicrobial peptides in maintaining urinary tract sterility.

Polymorphous light eruption: clinic aspects and pathogenesis

Polymorphous light eruption is an immunologically mediated photodermatosis with high prevalence, particularly among young women in temperate climates, characterized by pruritic skin lesions of variable morphology, occurring in spring or early summer on sun-exposed body sites. A resistance to ultraviolet radiation (UVR)-induced immunosuppression and a subsequent delayed-type hypersensitivity response to a photoantigen have been suggested as key factors in the disease. Molecular and immunologic disturbances associated with disease pathogenesis include a failure of skin infiltration by neutrophils and other regulatory immune cells on UVR exposure linked to a disturbed cytokine microenvironment. Standard management is based on prevention.

The consequences for human health of stratospheric ozone depletion in association with other environmental factors

Ozone depletion, climate and human health.

A novel subclass of bovine β-defensins links reproduction and immunology

β-defensins are effector molecules of the innate immune system, found in many diverse species. Their presence in invertebrates as well as vertebrates suggests highly conserved functional roles. Most β-defensins are believed to act as antimicrobial agents at epithelial surfaces, although additional functions have also been described, including immune regulatory activity, wound repair and a role in coat-colour determination. High expression of β-defensins have been found in testis and epididymidal epithelium as well as in the seminal fluid of humans, macaque, rat, mouse and cow. Human and macaque β-defensins have recently been shown to affect sperm motility while a mutation in β-defensin 126 is associated with reduced fertility in men. Genetic variation in bovine defensin genes may explain the increased incidence of low fertility in cattle. Here, we present a summary of the known functions of β-defensins as well as their emerging role in reproduction and their potential to improve fertility in cattle.

Human β-defensin 3 induces STAT1 phosphorylation, tyrosine phosphatase activity, and cytokine synthesis in T cells

The AMP hBD-3 stimulates numerous immune effector functions in myeloid cells and keratinocytes, predominantly through the MAPK signaling cascade. In contrast, hBD-3 was reported to neutralize the activation of T cells by antagonizing MAPK signaling initiated by SDF-1α through CXCR4. With the use of complementary proteomic and immunochemical approaches, we investigated possible stimulatory effects of hBD-3 on T cells and demonstrate that hBD-3 induces STAT1 tyrosine phosphorylation within 5 min yet is unable to induce MAPK activation. Inclusion of a PTPase inhibitor increased hBD-3-induced phosphorylation dramatically, suggesting that hBD-3 also stimulates PTPase activity concurrently. The increase in PTPase activity was confirmed by demonstrating that hBD-3 suppresses IFN-γ-induced STAT1 tyrosine phosphorylation but not STAT1 serine and ERK1/2 threonine phosphorylation and stimulates the translocation of SHP-2 into the nucleus within 15 min. The signaling pathways initiated by hBD-3 may lead to the observed enhancement of distinct T cell effector functions during TCR activation, such as the increase in IL-2 and IL-10, but not IFN-γ secretion. Thus, hBD-3 initiates distinct lineage-specific signaling cascades in various cells involved in host defense and induces a concurrent tyrosine kinase and tyrosine phosphatase signaling cascade that may activate simultaneously the targeted T cells and inhibit their response to other immune mediators. Furthermore, these results suggest that this evolutionarily conserved peptide, which exhibits a broad spectrum of antimicrobial and immunomodulatory activities, serves to integrate innate and adaptive immunity.

The Aryl hydrocarbon receptor is involved in UVR-induced immunosuppression

UVR suppresses the immune system through the induction of regulatory T cells (Tregs). UVR-induced DNA damage has been recognized as the major molecular trigger involved, as reduction of DNA damage by enhanced repair prevents the compromise to the immune system by UVR. Nevertheless, other signaling events may also be involved. The aryl hydrocarbon receptor (AhR) was identified as another target for UVR, as UVR activates the AhR and certain UVR effects were not detected in AhR-deficient cells. We studied whether the AhR is involved in UVR-induced local immunosuppression and whether similar effects can be induced by AhR agonists. The AhR antagonist 3-methoxy-4-nitroflavone reduced UVR-mediated immunosuppression and the induction of Tregs in murine contact hypersensitivity (CHS). Conversely, activation of the AhR by the agonist 4-n-nonylphenol (NP) suppressed the induction of CHS and induced antigen-specific Tregs similar to UVR. This was further confirmed in AhR knockout mice in which UVR- and NP-induced immunosuppression were significantly reduced. Together, this indicates that the AhR is involved in mediating UVR-induced immunosuppression. Activation of the AhR might represent an alternative to modulate the immune system in a similar manner like UVR but without causing the adverse effects of UVR, including DNA damage.

Intestinal antimicrobial peptides during homeostasis, infection, and disease

Antimicrobial peptides (AMPs), including defensins and cathelicidins, constitute an arsenal of innate regulators of paramount importance in the gut. The intestinal epithelium is exposed to myriad of enteric pathogens and these endogenous peptides are essential to fend off microbes and protect against infections. It is becoming increasingly evident that AMPs shape the composition of the commensal microbiota and help maintain intestinal homeostasis. They contribute to innate immunity, hence playing important functions in health and disease. AMP expression is tightly controlled by the engagement of pattern recognition receptors (PRRs) and their impairment is linked to abnormal host responses to infection and inflammatory bowel diseases (IBD). In this review, we provide an overview of the mucosal immune barriers and the intricate crosstalk between the host and the microbiota during homeostasis. We focus on the AMPs and pay particular attention to how PRRs promote their secretion in the intestine. Furthermore, we discuss their production and main functions in three different scenarios, at steady state, throughout infection with enteric pathogens and IBD.

Human beta-defensin 3 induces maturation of human langerhans cell-like dendritic cells: an antimicrobial peptide that functions as an endogenous adjuvant

Human beta-defensins (hBDs) are antimicrobial peptides that have an important role in innate immune responses at epithelial barriers such as the skin. However, the role that hBDs have in initiating cellular immune responses that contribute to antigen-specific adaptive immunity is not well understood. Here we show that one member of the hBD family, hBD3, can induce maturation and T-helper type 1 skewing function in human Langerhans cell-like dendritic cells (LC-DCs). Specifically, hBD3 potently induces phenotypic maturation of LC-DCs, including increased expression of CCR7, which mediates functional chemotactic responses to CCL19 and CCL21. hBD3-stimulated LC-DCs induce strong proliferation of and IFN-γ secretion by naive human T cells. hBD3 also induces phenotypic maturation of primary human skin-migratory DCs derived from human skin explants. These results suggest an important role for hBD3 in inducing DC activation, migration, and polarization. Thus, hBD3 contributes to the integration of innate and adaptive immune responses in the skin, and may be a useful adjuvant for skin immunization and an important factor in the pathophysiology of inflammatory skin diseases.

β-Defensins: multifunctional modulators of infection, inflammation and more?

Defensins comprise one of the largest groups of host defence peptides, present throughout evolution, in fungi and flowering plants as well as in invertebrates and vertebrates. These cysteine-rich, cationic peptides have a common ability to kill a broad range of microorganisms including bacteria, yeast and viruses. As such, they are a strong component of the arsenal that is an organism's innate immunity. It is becoming increasingly clear, however, that antimicrobial action is only one of the numerous roles of these multifunctional peptides. In recent years, the functions of defensins in immunomodulation have been widely investigated, and their involvement in other processes (such as fertility) is becoming evident. This review addresses recent advances in the immunomodulatory activity of β-defensins as well as the involvement of β-defensins in fertility, development, wound healing and cancer.