Human Defensins from antivirals to vaccine adjuvants: rediscovery of the innate immunity arsenal

Human defensins are a class of antimicrobial peptides, belonging to the innate immunity system. These peptides are expressed at the level of respiratory tract (both upper and lower) where they represent the first line of defense against pathogens; they are also known for their activity against different viruses, acting through diverse mechanisms, including direct binding to the virus, inhibition of viral replication, and aggregation of virions. It has been recently reported they are also effective against SARS-CoV-2. Moreover, they influence the immune response stimulating it in the challenge against microorganisms. An intriguingly potential application of defensin is related to their use as vaccine adjuvants; indeed, some in silico studies suggested their efficacy in boosting the immune response. Since the long-term persistence of acquired immunity against SARS-CoV-2 triggered by the currently employed vaccines is not known, natural agents with enhancing effects, such as defensins, administered with the vaccine, can be an interesting and attractive alternative.

Human defensins and Th-1 cytokines in hepatitis C viral infection

INTRODUCTION

active or chronic exacerbated forms of hepatitis C virus (HCV) infection subsequently progress to liver disease and human defensins has been determined to have some level of anti-viral properties invitro whilst the expression of T helper-1 cytokines is known to promote complete recovery from acute HCV infection. The study sought to determine relationship between these immune responses.

METHODS

a cross sectional descriptive study design was employed. Hundred and thirty-two individuals were assessed were assessed for to anti-HCV, HCV RNA, serum levels of human alpha defensins 1 (HAD-1) and human beta defensins 1 (HBD-1). T helper 1 cytokines (IL-2, IFN gamma, TNF alpha) secreted in serum were also analyzed using commercial ELISA assay. The study was conducted in Kumasi, Obuasi and Daboya in Ghana.

RESULTS

the serum mean concentrations of HAD-1, HBD-1, IL-2, IFN gamma and TNF alpha showed no significant difference in concentrations among participants with chronic, spontaneously recovered or negative to HCV infection (p>0.05). Persons with hepatitis B co-infection were more likely to develop chronic HCV infection (p=0.039). HAD-1 and HBD-1 showed significant positive association with IL-2 (p=0.000) whilst only HAD-1 positively correlated with IL-2 (p<0.000).

CONCLUSION

the immunological markers determined had no association with the status of HCV infection. HAD-1 increased with increasing levels of IL-2. These findings suggest that during HCV infection, inflammatory response through the production of cytokines by IL-2 cells may affect the release of HAD-1 and HBD-1.

Beneficial effect of probiotics on Pseudomonas aeruginosa-infected intestinal epithelial cells through inflammatory IL-8 and antimicrobial peptide human beta-defensin-2 modulation

The human pathogen Pseudomonas aeruginosa can rapidly induce fatal sepsis, even in previously healthy infants or children treated with appropriate antibiotics. To reduce antibiotic overuse, exploring novel complementary therapies, such as probiotics that reportedly protect patients against P. aeruginosa infection, would be particularly beneficial. However, the major mechanism underlying the clinical effects is not completely understood. We thus aimed to investigate how probiotics affect IL-8 and human beta-defensin 2 (hBD-2) in P. aeruginosa-infected intestinal epithelial cells (IECs). We infected SW480 IECs with wild type PAO1 P. aeruginosa following probiotic treatment with Lactobacillus rhamnosus GG or Bifidobacterium longum spp. infantis S12, and analysed the mRNA expression and secreted protein of IL-8 and hBD-2, Akt signalling and NOD1 receptor protein expression. We observed that probiotics enhanced hBD-2 expression but suppressed IL-8 responses when administered before infection. They also enhanced P. aeruginosa-induced membranous NOD1 protein expression and Akt activation. The siRNA-mediated Akt or NOD1 knockdown counteracted P. aeruginosa-induced IL-8 or hBD-2 expression, indicating regulatory effects of these probiotics. In conclusion, these data suggest that probiotics exert reciprocal regulation of inflammation and antimicrobial peptides in P. aeruginosa-infected IECs and provide supporting evidence for applying probiotics to reduce antibiotic overuse.

HNP-1 and HBD-1 as Biomarkers for the Immune Systems of Elite Basketball Athletes

Acute or strenuous exercise is sometimes related to upper respiratory tract infections in athletes. Practicing intense and regular exercise can lead to incorrect activation of the immune system, causing athletes to be excluded from training programs and competitions. Defensins are small antimicrobial peptides that are part of the innate immune system and dynamically involved in several biological activities. In this study, we highlight the role of human defensins in competitive basketball athletes. In particular, we consider the behavior of alpha- and beta-defensins together with white blood cells in a cohort of players. Moreover, we focus our attention on cortisol, a physiological indicator of stress, and testosterone, both of which are human hormones involved in muscle metabolism. The free-testosterone/cortisol ratio is considered to be an indicator of overtraining among athletes. This paper provides an up-to-date information of the role of human defensins as self-defense molecules during a continuous stressor such as long-term exercise, and it recognizes them as potential markers of infection.

Human Defensins: A Novel Approach in the Fight against Skin Colonizing Staphylococcus aureus

Staphylococcus aureus is a microorganism capable of causing numerous diseases of the human skin. The incidence of S. aureus skin infections reflects the conflict between the host skin′s immune defenses and the S. aureus’ virulence elements. Antimicrobial peptides (AMPs) are small protein molecules involved in numerous biological activities, playing a very important role in the innate immunity. They constitute the defense of the host′s skin, which prevents harmful microorganisms from entering the epithelial barrier, including S. aureus. However, S. aureus uses ambiguous mechanisms against host defenses by promoting colonization and skin infections. Our review aims to provide a reference collection on host-pathogen interactions in skin disorders, including S. aureus infections and its resistance to methicillin (MRSA). In addition to these, we discuss the involvement of defensins and other innate immunity mediators (i.e., toll receptors, interleukin-1, and interleukin-17), involved in the defense of the host against the skin disorders caused by S. aureus, and then focus on the evasion mechanisms developed by the pathogenic microorganism under analysis. This review provides the “state of the art” on molecular mechanisms underlying S. aureus skin infection and the pharmacological potential of AMPs as a new therapeutic strategy, in order to define alternative directions in the fight against cutaneous disease.

Human Enteric Defensin 5 Promotes Shigella Infection of Macrophages

Human α-defensins are 3- to 5-kDa disulfide-bridged peptides with a multitude of antimicrobial activities and immunomodulatory functions. Recent studies show that human enteric α-defensin 5 (HD5), a host defense peptide important for intestinal homeostasis and innate immunity, aids the highly infectious enteropathogen Shigella in breaching the intestinal epithelium in vitro and in vivo Whether and how HD5 influences Shigella infection of resident macrophages following its invasion of the intestinal epithelium remain poorly understood. Here, we report that HD5 greatly promoted phagocytosis of Shigella by macrophages by targeting the bacteria to enhance bacterium-to-cell contacts in a structure- and sequence-dependent fashion. Subsequent intracellular multiplication of phagocytosed Shigella led to massive necrotic cell death and release of the bacteria. HD5-promoted phagocytosis of Shigella was independent of the status of the type 3 secretion system. Furthermore, HD5 neither inhibited nor enhanced phagosomal escape of Shigella Collectively, these findings confirm a potential pathogenic role of HD5 in Shigella infection of not only epithelial cells but also macrophages, illuminating how an enteropathogen exploits a host protective factor for virulence and infection.

Critical determinants of human neutrophil peptide 1 for enhancing host epithelial adhesion of Shigella flexneri

Human neutrophil peptides (HNPs), also known as human myeloid α-defensins degranulated by infiltrating neutrophils at bacterial infection loci, exhibit broad antomicrobial activities against bacteria, fungi, and viruses. We have made a surprising recent finding that Shigella, a highly contagious, yet poorly adhesive enteric pathogen, exploits human α-defensins including HNP1 to enhance its adhesion to and invasion of host epithelial cells. However, the critical molecular determinants responsible for HNP1-enhanced Shigella adhesion and invasion have yet to be investigated. Using cultured epithelial cells and polarised Caco2 cells as an in vitro infection model, we demonstrated that HNP1 promoted Shigella infection in a structure- and sequence-dependent manner, with two bulky hydrophobic residues, Trp26 and Phe28 important for HNP1 self-assembly, being most critical. The functional importance of hydrophobicity for HNP1-enhanced Shigella infection was further verified by substitutions for Trp26 of a series of unnatural amino acids with straight aliphatic side chains of different lengths. Dissection of the Shigella infection process revealed that bacteria-rather than host cells-bound HNP1 contributed most to the enhancement. Further, mutagenesis analysis of bacterial surface components, while precluding the involvement of lipopolysaccharides (LPS) in the interaction with HNP1, identified outer membrane proteins and the Type 3 secretion apparatus as putative binding targets of HNP1 involved in enhanced Shigella adhesion and invasion. Our findings provide molecular and mechanistic insights into the mode of action of HNP1 in promoting Shigella infection, thus showcasing another example of how innate immune factors may serve as a double-edged sword in health and disease.

Human Paneth cell α-defensin-5 treatment reverses dyslipidemia and improves glucoregulatory capacity in diet-induced obese mice

Overnutrition is the principal cause of insulin resistance (IR) and dyslipidemia, which drive nonalcoholic fatty liver disease (NAFLD). Overnutrition is further linked to disrupted bowel function, microbiota alterations, and change of function in gut-lining cell populations, including Paneth cells of the small intestine. Paneth cells regulate microbial diversity through expression of antimicrobial peptides, particularly human α-defensin-5 (HD-5), and have shown repressed secretory capacity in human obesity. Mice were fed a 60% high-fat diet for 13 wk and subsequently treated with physiologically relevant amounts of HD-5 (0.001%) or vehicle for 10 wk. The glucoregulatory capacity was determined by glucose tolerance tests and measurements of corresponding insulin concentrations both before and during intervention. Gut microbiome composition was examined by 16S rRNA gene amplicon sequencing. HD-5-treated mice exhibited improved glucoregulatory capacity along with an ameliorated plasma and liver lipid profile. This was accompanied by specific decrease in jejunal inflammation and gut microbiota alterations including increased Bifidobacterium abundances, which correlated inversely with metabolic dysfunctions. This study provides proof of concept for the use of human defensins to improve host metabolism by mitigating the triad cluster of dyslipidemia, IR, and NAFLD.

Discovery and mechanisms of host defense to oncogenesis: targeting the β-defensin-1 peptide as a natural tumor inhibitor

Human beta-defensin-1 (hBD-1) is one of a number of small cationic host-defense peptides. Besides its well-known broad-spectrum antimicrobial function, hBD-1 has recently been identified as a chromosome 8p tumor-suppressor gene. The role of hBD-1 in modulating the host immune response to oncogenesis, associated with cell signaling and potential therapeutic applications, has become increasingly appreciated over time. In this study, multiple approaches were used to illustrate hBD-1 anti-tumor activities. Results demonstrate that hBD-1 peptide alters human epidermal growth factor receptor 2 (HER2) signal transduction and represses retroviral-mediated transgene expression in cancer cells. Loss of orthologous murine defense-1 (mBD1) in mice enhances nickel sulfate-induced leiomyosarcoma and causes mouse kidney cells to exhibit increased susceptibility to HPV-16 E6/7-induced neoplastic transformation. Furthermore, for the first time, a novel function of the urine-derived hBD-1 peptide was discovered to suppress bladder cancer growth and this may lead to future applications in the treatment of malignancy.

Interplay of Immunity and Vitamin D: Interactions and Implications with Current IBD Therapy

Crohn's disease (CD) and ulcerative colitis (UC) are classified under inflammatory bowel disease (IBD) which has been linked to a multifaceted etiology involving both environmental and genetic factors that intersect with the vitamin D pathway. Dysfunctions in innate immune defense mechanisms in the epithelial compartment of the intestine play a crucial role in the pathogenesis of IBD. Symptoms of IBD are caused by excessive immune responses to luminal bacteria, and vitamin D has been shown to play a role in intestinal defense by aiding in the suppression of microbial invasion into the epithelium. Vitamin D, as an immunomodulator, can modify the innate immune response of the body. Vitamin D attenuates the transcription of pro-inflammatory cytokines that are upregulated in the event of epithelial stress common in patients with IBD. Vitamin D deficiency was identified in 82% of IBD patients compared to the 31% national average and has been linked to defective epithelial processes at both genomic and proteomic levels. Mucosal damage and an impaired immune response are at the center of IBD, and vitamin D aids in sustaining the structural integrity of epithelial cells while enhancing innate immune responses in the mucosa. Here we provide a systematic review of the pathophysiological effects of cytokines in IBD in the presence of vitamin D deficiency. Also, analysis of the immunomodulatory effect of vitamin D in regulating immunopathogenic factors like chemokines, growth factors, and human defensins will enhance knowledge of the underlying molecular mechanisms of the therapeutic role of vitamin D in IBD and thus aid in the development of better patient management strategies.

A bacterial mutant library as a tool to study the attack of a defensin peptide

Defensin attack! Here we report the screening of human defensin 5 against the Keio Collection of E. coli strains. The results of this screen further our understanding of how this important hostdefense peptide kills bacteria and how bacteria protect themselves against the attack from the human host.