Vitamin D regulation of cathelicidin in the skin: toward a renaissance of vitamin D in dermatology?

Is Vitamin D3 a Worthy Supplement Protecting against Secondary Infections in Dogs with Atopic Dermatitis?

Canine atopic dermatitis (CAD) is a common, chronic, inflammatory skin disease in dogs worldwide. This disease often predisposes for secondary organisms overgrowth and skin infections with pathogens, such as Staphylococcus pseudintermedius and Malassezia pachydermatis. Unfortunately, the causes of this disease in both humans and animals are not fully understood; therefore, the only possible option is a lifelong, symptomatic treatment. The management of CAD is mainly based on limiting contact with allergens and antipruritic therapy, most often with glucocorticoids and antihistamines. A serious problem in this situation is the fact, that long-term administration of glucocorticoids leads to side effects like polyuria, alopecia, increased susceptibility to infection, muscle atrophy, and many others. For this reason, great emphasis is placed on the development of replacement and supportive therapies. It is a well-documented fact that reduced concentrations of serum vitamin D3 contribute to the severity of atopic dermatitis symptoms in humans. Moreover, unlike the most commonly used therapeutic methods, of which the main goal is to ameliorate inflammation and pruritus, namely the symptoms of AD, vitamin D3 supplementation affects some underlying factors of this disease. Therefore, in this review, we summarize the current state of knowledge regarding the role of vitamin D3 in CAD, its protective effect against secondary bacterial and fungal infections, and the potential of its supplementation in dogs.

Emerging Roles of Vitamin D-Induced Antimicrobial Peptides in Antiviral Innate Immunity

Vitamin D deficiency, characterized by low circulating levels of calcifediol (25-hydroxyvitamin D, 25D) has been linked to increased risk of infections of bacterial and viral origin. Innate immune cells produce hormonal calcitriol (1,25-dihydroxyvitamin D, 1,25D) locally from circulating calcifediol in response to pathogen threat and an immune-specific cytokine network. Calcitriol regulates gene expression through its binding to the vitamin D receptor (VDR), a ligand-regulated transcription factor. The hormone-bound VDR induces the transcription of genes integral to innate immunity including pattern recognition receptors, cytokines, and most importantly antimicrobial peptides (AMPs). Transcription of the human AMP genes β-defensin 2/defensin-β4 (HBD2/DEFB4) and cathelicidin antimicrobial peptide (CAMP) is stimulated by the VDR bound to promoter-proximal vitamin D response elements. HDB2/DEFB4 and the active form of CAMP, the peptide LL-37, which form amphipathic secondary structures, were initially characterized for their antibacterial actively. Notably, calcitriol signaling induces secretion of antibacterial activity in vitro and in vivo, and low circulating levels of calcifediol are associated with diverse indications characterized by impaired antibacterial immunity such as dental caries and urinary tract infections. However, recent work has also provided evidence that the same AMPs are components of 1,25D-induced antiviral responses, including those against the etiological agent of the COVID-19 pandemic, the SARS-CoV2 coronavirus. This review surveys the evidence for 1,25D-induced antimicrobial activity in vitro and in vivo in humans and presents our current understanding of the potential mechanisms by which CAMP and HBD2/DEFB4 contribute to antiviral immunity.

Nutrition and youthful skin

Nutrition and dietary supplements have been used to promote a youthful appearance for millennia. Despite high public demand for these products, evidence supporting their efficacy is limited and often inconsistent. We discuss the structural and functional changes that occur in the skin during the aging process. We also review evidence supporting the use of nutritional supplements commonly used to promote a youthful appearance, including essential fatty acids, coenzyme Q, collagen peptides, curcumin, polyphenols, flavonoids, probiotics, silymarin, and vitamins A, C, D, and E. We also consider the role of advanced glycosylated end products, antiinflammatory diets, and caloric restriction in delaying premature skin aging. Although evidence supporting the use of some dietary interventions is promising, further long-term studies in humans are required to fully understand their effects on the promotion of a youthful appearance.

Cathelicidin Contributes to the Restriction of Leishmania in Human Host Macrophages

In cutaneous Leishmaniasis the parasitic control in human host macrophages is still poorly understood. We found an increased expression of the human cathelicidin CAMP in skin lesions of Ethiopian patients with cutaneous leishmaniasis. Vitamin D driven, Cathelicidin-type antimicrobial peptides (CAMP) play an important role in the elimination of invading microorganisms. Recombinant cathelicidin was able to induce cell-death characteristics in Leishmania in a dose dependent manner. Using human primary macrophages, we demonstrated pro-inflammatory macrophages (hMDM1) to express a higher level of human cathelicidin, both on gene and protein level, compared to anti-inflammatory macrophages (hMDM2). Activating the CAMP pathway using Vitamin D in hMDM1 resulted in a cathelicidin-mediated-Leishmania restriction. Finally, a reduction of cathelicidin in hMDM1, using a RNA interference (RNAi) approach, increased Leishmania parasite survival. In all, these data show the human cathelicidin to contribute to the innate immune response against Leishmaniasis in a human primary cell model.

Oral vitamin D3 5000 IU/day as an adjuvant in the treatment of atopic dermatitis: a randomized control trial

BACKGROUND

Vitamin D has immunomodulatory effects both in the innate and adaptive immune systems, and there is growing scientific evidence demonstrating its relevance in inflammatory processes such as AD.

HYPOTHESIS

If vitamin D3 promotes the skin immune system, then it should improve the response to treatment of patients with AD.

METHODS

A randomized, double-blind placebo-controlled clinical trial was conducted, which included 65 patients with AD according to Hanifin-Rajka criteria and the severity scale (SCORAD). The patients were divided into two groups to receive either vitamin D3 5000 IU/day (n = 33) or placebo (n = 32), plus baseline therapy (topical steroid, soap substitute, and emollient) during 3 months.

RESULTS

Fifty-eight of the 65 enrolled subjects were included in the analysis. At the end of the intervention, the treated group achieved higher levels of 25(OH)D (P < 0.001). At week 12, those patients who registered serum levels of 25(OH)D ≥20 ng/ml, regardless of whether or not they had received supplementation, showed a lower SCORAD compared to those with levels <20 ng/ml (P < 0.001). Eighty percent of the patients with serum levels <20 ng/ml (n = 9) had moderate-severe AD despite standard treatment. Vitamin D levels ≥20 ng/ml associated with baseline therapy strongly favored remission of atopic dermatitis (P = 0.03). No significant differences were found between patients with serum levels of ≥20 ng/ml vs. ≥30 ng/ml.

CONCLUSIONS

Reaching serum levels of 25(OH)D > 20 ng/ml in conjunction with standard therapy is sufficient to achieve a reduction in severity (SCORAD) in patients with AD.

Cathelicidin augments VDR-dependent anti-leishmanial immune response in Indian Post-Kala-Azar Dermal Leishmaniasis

OBJECTIVES

Indian Post kala-azar dermal leishmaniasis (PKDL) is the cutaneous aftermath of visceral leishmaniasis (VL) caused by L. donovani. Vitamin D-regulated cationic antimicrobial peptide cathelicidin (hCAP-18/LL-37) has microbicidal and immunomodulatory role against cutaneous infections, but its role in PKDL remains elusive.

METHODS

Skin snips and blood-derived monocytes of PKDL patients (n=46), before (BT) and after (AT) chemotherapy, were used for this study. Serum vitamin D3 level was evaluated by ELISA. Cathelicidin and vitamin D receptor (VDR) levels were analyzed by real-time PCR and flowcytometry in PKDL patients. The mechanistic effect of cathelicidin on macrophage differentiation and anti-leishmanial activity was assessed through RNA interference techniques followed by subsequent microscopic evaluation of in vitro parasite killing and Th1/Th2 counter-regulation by ELISA/RT-PCR.

RESULTS

Low vitamin D3 levels were accompanied with decreased expression of cathelicidin and VDR in PKDL-BT patients. Results suggested positive induction of VDR-dependent cathelicidin in PKDL macrophages by Amphotericin B treatment, which could be due to indirect effect of drug-induced IL12 upregulation. 1,25-Vitamin D3 stimulation induced cathelicidin in PKDL-BT patients through involvement of TLR2/IL-1β, but not TLR4. Cathelicidin also augmented the anti-leishmanial effect and macrophage activating potential of Amphotericin B, attributable to regulation of VDR-dependent enhancement of CD40, p-STAT-I and MHC-II expression leading to regulation of IL10/IL12 balance in PKDL-BT patient macrophages.

CONCLUSIONS

This study indicates that cathelicidin augments anti-leishmanial macrophage activating property of Amphotericin B in a TLR2/VDR dependent mechanism, and advocate the development of novel adjunct treatment modality of cathelicidin with conventional Amphotericin B in PKDL patients.

Intestinal epithelial vitamin D receptor deletion leads to defective autophagy in colitis

OBJECTIVE

Vitamin D and the vitamin D receptor (VDR) appear to be important immunological regulators of inflammatory bowel diseases (IBD). Defective autophagy has also been implicated in IBD, where interestingly, polymorphisms of genes such as ATG16L1 have been associated with increased risk. Although vitamin D, the microbiome and autophagy are all involved in pathogenesis of IBD, it remains unclear whether these processes are related or function independently.

DESIGN

We investigated the effects and mechanisms of intestinal epithelial VDR in healthy and inflamed states using cell culture models, a conditional VDR knockout mouse model (VDR(ΔIEC)), colitis models and human samples.

RESULTS

Absence of intestinal epithelial VDR affects microbial assemblage and increases susceptibility to dextran sulfate sodium-induced colitis. Intestinal epithelial VDR downregulates expressions of ATG16L1 and lysozyme, and impairs antimicrobial function of Paneth cells. Gain and loss-of-function assays showed that VDR levels regulate ATG16L1 and lysozyme at the transcriptional and translational levels. Moreover, low levels of intestinal epithelial VDR correlated with reduced ATG16L1 and representation by intestinal Bacteroides in patients with IBD. Administration of the butyrate (a fermentation product of gut microbes) increases intestinal VDR expression and suppresses inflammation in a colitis model.

CONCLUSIONS

Our study demonstrates fundamental relationship between VDR, autophagy and gut microbial assemblage that is essential for maintaining intestinal homeostasis, but also in contributing to the pathophysiology of IBD. These insights can be leveraged to define therapeutic targets for restoring VDR expression and function.

Skin Metabolites Define a New Paradigm in the Localization of Skin Tropic Memory T Cells

The localization of memory T cells to human skin is essential for long-term immune surveillance and the maintenance of barrier integrity. The expression of CCR8 during naive T cell activation is controlled by skin-specific factors derived from epidermal keratinocytes and not by resident dendritic cells. In this study, we show that the CCR8-inducing factors are heat stable and protease resistant and include the vitamin D3 metabolite 1α,25-dihydroxyvitamin D3 and PGE2. The effect of either metabolite alone on CCR8 expression was weak, whereas their combination resulted in robust CCR8 expression. Elevation of intracellular cAMP was essential because PGE2 could be substituted with the adenylyl cyclase agonist forskolin, and CCR8 expression was sensitive to protein kinase A inhibition. For effective induction, exposure of naive T cells to these epidermal factors needed to occur either prior to or during T cell activation even though CCR8 was only detected 4-5 d later in proliferating T cells. The importance of tissue environments in maintaining cellular immune surveillance networks within distinct healthy tissues provides a paradigm shift in adaptive immunity. Epidermal-derived vitamin D3 metabolites and PGs provide an essential cue for the localization of CCR8(+) immune surveillance T cells within healthy human skin.

Sphingolipids and antimicrobial peptides: function and roles in atopic dermatitis

Inflammatory skin diseases such as atopic dermatitis (AD) and rosacea were complicated by barrier abrogation and deficiency in innate immunity. The first defender of epidermal innate immune response is the antimicrobial peptides (AMPs) that exhibit a broad-spectrum antimicrobial activity against multiple pathogens, including Gram-positive and Gram-negative bacteria, viruses, and fungi. The deficiency of these AMPs in the skin of AD fails to protect our body against virulent pathogen infections. In contrast to AD where there is a suppression of AMPs, rosacea is characterized by overexpression of cathelicidin antimicrobial peptide (CAMP), the products of which result in chronic epidermal inflammation. In this regard, AMP generation that is controlled by a key ceramide metabolite S1P-dependent mechanism could be considered as alternate therapeutic approaches to treat these skin disorders, i.e., Increased S1P levels strongly stimulated the CAMP expression which elevated the antimicrobial activity against multiple pathogens resulting the improved AD patient skin.

The pleiotropic effect of vitamin d

The novel roles of vitamin D were discovered and valued in this century. In addition to the maintenance of calcium and phosphorus balance, vitamin D regulates the function of the kidneys, heart, and immune system. Moreover, its anti-inflammatory, antiapoptotic, and antifibrotic roles have gained considerable attention. Vitamin D is also important for the maintenance of homeostasis by regulation of hormone secretion, cell proliferation, and differentiation. This paper will review these pleiotropic functions of vitamin D.

Recent advances in the field of antimicrobial peptides in inflammatory diseases

Antimicrobial peptides are cationic molecules, which participate in multiple aspects of the immune response including the control of inflammatory diseases, characteristic that make these molecules attractive as therapeutic tools. These peptides are produced in bacteria, insects, plants and vertebrates, and are classified together due to their capacity to directly inhibit the growth of microorganisms, and to regulate the immune response by inducing the secretion of chemokines and cytokines. Various families of antimicrobial peptides have been identified including the cathelicidins and defensins, the most investigated human antimicrobial peptides. This review will cover the main biological functions of antimicrobial and cell-penetrating peptides in inflammation, and describe the importance and utility of antimicrobial peptides as therapeutics for inflammatory diseases.

Use of vitamin D in various disorders

Approximately 1 billion people worldwide have been identified as vitamin D deficient in the 21st century, and the number is on the rise; non-classical actions of vitamin D were initially recognized around 30 y ago when receptors for vitamin D were detected in neoplastic cells lines. The aim of this review is to provide a brief overview of the non-classical actions of vitamin D. Reports describing the associations of non skeletal actions of vitamin D, especially pertaining to the immune system, inflammatory disorders, cancers and cardiovascular disease have been summarized in this paper. Reports support a role for the active form of vitamin D in mediating normal function of both the innate and adaptive immune systems. Studies also suggest a link between vitamin D deficiency and autoimmune diseases, such as rheumatoid arthritis, systemic sclerosis, systemic lupus erythematosus and type 1 diabetes. There is believed to be an inverse association between serum 25-hydroxyvitamin D concentrations and the incidence of colorectal cancer, sporadic colorectal adenoma and breast cancer. Vitamin D deficiency has been linked with various cardiovascular diseases such as hypertension, myocardial infarction, and stroke. Several epidemiological and genetic studies suggest a strong association between vitamin D and non skeletal acute and chronic disorders. However, currently, robust clinical data are still lacking to support raising intake requirements and target vitamin D plasma levels. Nonetheless, the high prevalence of vitamin D deficiency is alarming and requires implementation of clear supplementation guidelines.

Cathelicidin LL-37: an antimicrobial peptide with a role in inflammatory skin disease

Chronic inflammatory skin diseases such as atopic dermatitis, psoriasis or rosacea are very common. Although their exact pathogenesis is not completely understood all three diseases are characterized by dysregulation of cutaneous innate immunity. Cathelicidin LL-37 is an important effector molecule of innate immunity in the skin and atopic dermatitis, psoriasis or rosacea show defects in cathelicidin expression, function or processing. In atopic dermatitis, cathelicidin induction might be disturbed resulting in defective antimicrobial barrier function. In contrast, psoriasis is characterized by overexpression of cathelicidin. However to date it is unclear whether pro- or anti-inflammatory functions of cathelicidin predominate in lesional skin in psoriasis. In rosacea, cathelicidin processing is disturbed resulting in peptide fragments causing inflammation, erythema and telangiectasias. In this review, the current evidence on the role of cathelicidin LL-37 in the pathogenesis of inflammatory skin diseases will be outlined. As cathelicidin LL-37 might also serve as a future treatment target potential novel treatment strategies for those diseases will be discussed.

Vitamins and cutaneous wound healing

BACKGROUND

Vitamins have long been thought to modulate the various stages of wound healing through a variety of proposed mechanisms. Our goal was to investigate relevant studies examining the role of different vitamins in wound healing.

METHODS

MEDLINE, Cochrane Database of Systematic Reviews, and Google Scholar were searched for basic science and clinical studies examining the role of vitamins as adjuncts in wound healing.

RESULTS

Mechanisms of action for each of the vitamins are reviewed. It was suggested by many of the studies that the major vitamins A, C, E, D, K, and B have demonstrated utility as adjuncts in wound care in basic science and clinical trials.

CONCLUSION

There is a vast amount of literature on the effect of vitamins on wound healing at the basic science level. Further understanding and controlled trials will help better understand how to utilize vitamins in wound care.

DECLARATION OF INTEREST

None.

Atopic dermatitis - from new pathophysiologic insights to individualized therapy

Recently, important novel insights into the complex pathophysiology of atopic dermatitis (AD) have been gained. However, in most cases the therapy of AD is limited to base line therapy with emollients combined with symptomatic, rather general immunosuppressive treatment approaches of the flare-ups. Latest research findings together with experiences from daily clinical practice, which support the concept that a combination of general disease features together with specific trigger factors in the individual patients drive the disease, might be helpful for a subclassification of patients with AD based on the most relevant pathophysiologic modifications. Subclassification of patients with AD seems indispensable to introduce rationale-based, individualized treatment approaches of AD, which target specific modified pathways. In this review, we provide an overview about a selection of pathophysiologic pathways, which hold promise to represent targets of such therapeutic approaches in the near future.

The Role of Vitamin D in Human Health: A Paradigm Shift

Vitamin D deficiency is pandemic, spanning many continents and including all ages, genders and racial/ethnic groups. Currently, world-wide attention is focused on the importance of vitamin D in optimizing health and preventing disease. This focus is largely the result of the scientific discovery that vitamin D receptors are present in nearly every tissue and cell in the body and that adequate vitamin D status is essential for optimal functioning of these tissues and cells. An impressive body of research has accumulated over the past two decades providing new information about the role of vitamin D in prevention of a broad range of diseases. The purpose of this paper is to provide a review of this new information.

Vitamin d and pancreatic cancer-an update

The non-classical actions of vitamin D, namely anti-proliferation, pro-differentiation, immune function modulation, and anti-inflammation, have received great attention during the past decade, in particular, the potential of vitamin D analogs alone or in combination with other anticancer agents for the treatment of a variety of cancers. The association between vitamin D status and the higher incidence of many forms of cancer has suggested that vitamin D may play a role in the etiology of these types of cancer. Although it is still controversial whether this association exists for pancreatic cancer, biochemical evidence clearly indicates pancreatic cancer cells are responsive to the inhibitory effect of vitamin D and its analogs. In this review, we discuss briefly the origin and current therapy of pancreatic cancer, the history, source, metabolism and functions of vitamin D, the recent progress in the epidemiological studies of sunlight, and vitamin D status, and biochemical studies of vitamin D analogs in the prevention and treatment of pancreatic cancer.

Vitamin D, vitamin D receptor, and cathelicidin in the treatment of tuberculosis

Vitamin D plays a major role in bone mineral density and calcium homeostasis. Apart from its classical action, the active form of vitamin D [1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3))] influences the innate and adaptive immune functions through vitamin D receptor (VDR) that are present in various cells of the immune system. Vitamin D deficiencies have been associated with development of tuberculosis (TB) disease, caused by Mycobacterium tuberculosis. Vitamin D(3) is shown to enhance macrophage phagocytosis of M. tuberculosis and increases the production of antimicrobial peptide cathelicidin and killing of M. tuberculosis. During the preantibiotic era, exposure to sunlight and supplementation of vitamin D were the methods of choice for treatment of TB. Vitamin D supplementation showed sputum clearance and radiological improvement and reduction in mortality among human immunodeficiency virus (HIV)-infected patients with TB. VDR gene polymorphisms regulate the immunomodulatory effect of vitamin D(3) and are associated with faster sputum conversion during anti-TB treatment. The emerging evidences regarding immunomodulatory properties of vitamin D(3) have rekindled interest in vitamin D as an adjunct to anti-TB therapy. The current review explains the important potential application of vitamin D in enhancing the innate immunity to TB and the role of VDR gene variants on anti-TB treatment.

Rosacea treatments: What's new and what's on the horizon?

Rosacea is a common, chronic, cutaneous disorder presenting with recurrent episodes of facial flushing, erythema, papules, pustules and telangiectasias. It is a multifactorial disease and its various clinical presentations probably represent the consequence of combined different triggers upon a specific background. Its management is largely based on long-established treatments empirically tailored to the specific presenting symptoms and no real breakthrough has occurred to date. However, recent insights into the still rather obscure pathophysiology of rosacea seem to open the way for etiologically oriented treatments. These may include, on the one side, the more effective application of traditional drugs, such as tetracyclines and metronidazole, to specifically selected patients or, on the other side, new therapeutic options, such as vitamin D receptor antagonists. It is to be remarked that the quality of most studies evaluating rosacea treatment is rather poor, mainly due to a lack of proper standardization. For a major breakthrough to occur in the management of rosacea, we need both a better understanding of its pathogenesis and the adherence of future clinical trials to clearly defined grading and inclusion criteria, which are crucial for investigators to correctly compare and interpret the results of their work.

Vitamin D as an inducer of cathelicidin antimicrobial peptide expression: past, present and future

Vitamin D was discovered as the preventive agent of nutritional rickets, a defect in bone development due to inadequate uptake of dietary calcium. However, a variety of studies over the last several years has revealed that vitamin D controls much more than calcium homeostasis. For example, recent research has underlined the key role of vitamin D signaling in regulation of innate immunity in humans. Vitamin D is converted to 25-hydroxyvitamin D (25D), its major circulating form, and then to hormonal 1,25-dihydroxyvitamin D (1,25D) in target cells. We now know that when cells of the immune system such a macrophages sense a bacterial infection they acquire the capacity to convert circulating 25D into 1,25D. Moreover, 1,25D thus produced is a direct inducer of expression of genes encoding antimicrobial peptides, in particular cathelicidin antimicrobial peptide (CAMP). Antimicrobial peptides such as CAMP are vanguards of innate immune responses to bacterial infection and can act as signaling molecules to regulate immune system function. This review covers what we have learned in the past few years about the expression and function of CAMP under physiological and pathophysiological conditions, and addresses the potential future applications of vitamin D analogues to therapeutic regulation of CAMP expression.

Update in vitamin D

The past decade, particularly the last 18 months, witnessed a vigorous increase in interest in vitamin D from both the lay and biomedical worlds. Much of the growing interest in vitamin D is powered by new data being extracted from the National Health and Nutrition Examination Survey (NHANES). The newest statistics demonstrate that more than 90% of the pigmented populace of the United States (Blacks, Hispanics, and Asians) now suffer from vitamin D insufficiency (25-hydroxyvitamin D <30 ng/ml), with nearly three fourths of the white population in this country also being vitamin D insufficient. This represents a near doubling of the prevalence of vitamin D insufficiency seen just 10 yr ago in the same population. This review attempts to provide some explanation for: 1) the rapid decline in vitamin D status in the United States; 2) the adverse impact of vitamin D insufficiency on skeletal, infectious/inflammatory, and metabolic health in humans; and 3) the therapeutic rationale and reliable means for vigorous supplementation of our diets with vitamin D.

Antimicrobial peptides: general overview and clinical implications in human health and disease

Antimicrobial peptides (AMPs) are evolutionarily conserved molecules involved in the defense mechanisms of a wide range of organisms. Produced in bacteria, insects, plants and vertebrates, AMPs protect against a broad array of infectious agents. In mammals these peptides protect against bacteria, viruses, fungi, and certain parasites. Recently, novel biologic effects of AMPs have been documented such as endotoxin neutralization, chemotactic and immunomodulating activities, induction of angiogenesis and wound repair. Thus these ancestral molecules are crucial components of the innate immune system and attractive candidates for novel therapeutic approaches. This review focuses on cathelicin and defensins, the most documented human AMPs, and discusses their antimicrobial activity and pleiotropic immunomodulating effects on inflammatory and infectious diseases.

Peptide-based Antifungal Therapies against Emerging Infections

Acquired drug resistance to mycotic infections is rapidly emerging as a major medical problem. Opportunistic fungal infections create therapeutic challenges, particularly in high risk immunocompromised patients with AIDS, cancer, and those undergoing transplantation. Higher mortality and/or morbidity rates due to invasive mycosis have been increasing over the last 20 years, and in light of growing resistance to commonly used antibiotics, novel antifungal drugs and approaches are required. Currently there is considerable interest in antifungal peptides that are ubiquitous in plant and animal kingdoms. These small cationic peptides may have specific targets or may be multifunctional in their mechanism of action. On the basis of recent advances in protein engineering and solid phase syntheses, the utility and potential of selected peptides as efficient antifungal drugs with acceptable toxicity profiles are being realized. This review will discuss recent advances in peptide therapy for opportunistic fungal infections.

The roles of cathelicidin LL-37 in immune defences and novel clinical applications

PURPOSE OF REVIEW

LL-37 is the only member of the cathelicidin family of host defence peptides expressed in humans. It is primarily produced by phagocytic leucocytes and epithelial cells, and mediates a wide range of biological responses: direct killing of microorganisms, chemotaxis and chemokine induction, regulation of inflammatory responses, as well as adjuvant, angiogenic and wound healing effects. In this review we will cover the recent advances in the understanding of LL-37 biology: its activities, the mechanisms of its induction and roles in immune defence.

RECENT FINDINGS

Recent studies advanced our understanding of the mechanisms controlling LL-37 expression, demonstrating the key involvement of the vitamin D3 and the hypoxia response pathways, and the impacts of commensal and pathogenic microorganisms on its production. The synergistic and antagonistic interactions between LL-37 and other immune mediators have been further elucidated. Furthermore, studies in animal models and human patients further characterized the roles of cathelicidins in immunity, with roles in infectious and inflammatory conditions. The underlying properties of LL-37 have been exploited to create innate defence regulator peptides that represent a novel immunomodulatory approach to treating infections.

SUMMARY

The understanding of the biological properties and functions of LL-37 and other host defence peptides advances our knowledge of innate immunity, the interactions of the host with pathogens and the microflora, as well as the pathology of infectious and inflammatory diseases, creating many strategies and opportunities for therapeutic intervention.