Defensins in viral infections

Etiology of viral induced acute liver failure and defensins as potential therapeutic agents in ALF treatment

Acute liver failure (ALF) is a rare and severe disease, which, despite continuous advances in medicine, is still characterized by high mortality (65-85%). Very often, a liver transplant is the only effective treatment for ALF. Despite the implementation of prophylactic vaccinations in the world, the viral background of ALF is still a problem and leads to many deaths. Depending on the cause of ALF, it is sometimes possible to reverse this condition with appropriate therapies, which is why the search for effective antiviral agents seems to be a very desirable direction of research. Defensins, which are our natural antimicrobial peptides, have a very high potential to be used as therapeutic agents for infectious liver diseases. Previous studies on the expression of human defensins have shown that increased expression of human α and β-defensins in HCV and HBV infections is associated with a better response to treatment. Unfortunately, conducting clinical trials for ALF is very difficult due to the severity of the disease and the low incidence, therefore animal models are important for the development of new therapeutic strategies. One of the best animal models that has real reference to research on acute liver failure (ALF) is rabbit hemorrhagic disease in rabbits caused by the Lagovirus europaeus virus. So far, there have been no studies on the potential of defensins in rabbits infected with Lagovirus europaeus virus.

β-Defensin-1 Regulates Influenza Virus Infection in Human Bronchial Epithelial Cells through the STAT3 Signaling Pathway

Understanding the host response to influenza A virus (IAV) infection is vital for developing intervention strategies. The primary barriers for invading respiratory pathogens are the respiratory tract epithelial cells and antimicrobial proteins generated by these cells. The antimicrobial peptide, β-defensin-1, has antiviral activity against both enveloped and non-enveloped viruses. Significant downregulation of β-defensin1 gene (DEFB1) expression was observed when human bronchial epithelial cells (HBEpCs) were exposed to IAV. HBEpCs overexpressing DEFB1 caused a significant reduction in IAV, that was confirmed by IAV matrix gene analysis, plaque assay, and confocal microscopy. DEFB1 expression after transfection with two micro RNAs (miRNAs), hsa-miR-186-5p and hsa-miR-340-5p, provided evidence that DEFB1 expression could be modulated by these miRNAs and hsa-miR-186-5p had a higher binding efficiency with DEFB1. Overexpression of DEFB1 in IAV-infected HBEpCs led to increased NF-κB expression. In a PCR array analysis of 84 transcription factors, either overexpressing DEFB1 or siRNA silencing of DEFB1 expression significantly modulated the expression of signal transducer and activator of transcription 3 (STAT3). In addition, Ingenuity Pathway Analysis (IPA) integrated with PCR array data showed that the JAK1/STAT3 pathway was significantly altered in cells overexpressing DEFB1, suggesting this to be one of the pathways by which defensin regulates IAV replication in HBEpCs. In conclusion, the reduction in IAV copy number in DEFB1 overexpressing cells suggests that β-defensin-1 plays a key role in regulating IAV survival through STAT3 and is a potential target for antiviral drug development.

The molecular basis of differential host responses to avian influenza viruses in avian species with differing susceptibility

Introduction

Highly pathogenic avian influenza (HPAI) viruses, such as H5N1, continue to pose a serious threat to animal agriculture, wildlife and to public health. Controlling and mitigating this disease in domestic birds requires a better understanding of what makes some species highly susceptible (such as turkey and chicken) while others are highly resistant (such as pigeon and goose). Susceptibility to H5N1 varies both with species and strain; for example, species that are tolerant of most H5N1 strains, such as crows and ducks, have shown high mortality to emerging strains in recent years. Therefore, in this study we aimed to examine and compare the response of these six species, to low pathogenic avian influenza (H9N2) and two strains of H5N1 with differing virulence (clade 2.2 and clade 2.3.2.1) to determine how susceptible and tolerant species respond to HPAI challenge.

Methods

Birds were challenged in infection trials and samples (brain, ileum and lung) were collected at three time points post infection. The transcriptomic response of birds was examined using a comparative approach, revealing several important discoveries.

Results

We found that susceptible birds had high viral loads and strong neuro-inflammatory response in the brain, which may explain the neurological symptoms and high mortality rates exhibited following H5N1 infection. We discovered differential regulation of genes associated with nerve function in the lung and ileum, with stronger differential regulation in resistant species. This has intriguing implications for the transmission of the virus to the central nervous system (CNS) and may also indicate neuro-immune involvement at the mucosal surfaces. Additionally, we identified delayed timing of the immune response in ducks and crows following infection with the more deadly H5N1 strain, which may account for the higher mortality in these species caused by this strain. Lastly, we identified candidate genes with potential roles in susceptibility/resistance which provide excellent targets for future research.

Discussion

This study has helped elucidate the responses underlying susceptibility to H5N1 influenza in avian species, which will be critical in developing sustainable strategies for future control of HPAI in domestic poultry.

Fusion-inhibition peptide broadly inhibits influenza virus and SARS-CoV-2, including Delta and Omicron variants

Pandemic influenza virus and SARS-CoV-2 vaiants have posed major global threats to public health. Broad-spectrum antivirals blocking viral entry can be an effective strategy for combating these viruses. Here, we demonstrate a frog-defensin-derived basic peptide (FBP), which broadly inhibits the influenza virus by binding to haemagglutinin so as to block low pH-induced HA-mediated fusion and antagonizes endosomal acidification to inhibit the influenza virus. Moreover, FBP can bind to the SARS-CoV-2 spike to block spike-mediated cell–cell fusion in 293T/ACE2 cells endocytosis. Omicron spike shows a weak cell–cell fusion mediated by TMPRSS2 in Calu3 cells, making the Omicron variant sensitive to endosomal inhibitors. In vivo studies show that FBP broadly inhibits the A(H1N1)pdm09 virus in mice and SARS-CoV-2 (HKU001a and Delta)in hamsters. Notably, FBP shows significant inhibition of Omicron variant replication even though it has a high number of mutations in spike. In conclusion, these results suggest that virus-targeting FBP with a high barrier to drug resistance can be an effective entry-fusion inhibitor against influenza virus and SARS-CoV-2 in vivo.

Association between Immunologic Markers and Cirrhosis in Individuals from a Prospective Chronic Hepatitis C Cohort

Background: Chronic hepatitis C virus (HCV) infection can affect immune response and inflammatory pathways, leading to severe liver diseases such as cirrhosis and hepatocellular carcinoma (HCC). Methods: In a prospective cohort of chronically HCV-infected individuals, we sampled 68 individuals who developed cirrhosis, 91 controls who did not develop cirrhosis, and 94 individuals who developed HCC. Unconditional odds ratios (ORs) from polytomous logistic regression models and canonical discriminant analyses (CDAs) were used to compare categorical (C) baseline plasma levels for 102 markers in individuals who developed cirrhosis vs. controls and those who developed HCC vs. cirrhosis. Leave-one-out cross validation was used to produce receiver operating characteristic curves to assess predictive ability of markers. Lastly, biological pathways were assessed in association with cirrhotic development compared to controls. Results: After multivariable adjustment, DEFA-1 (OR: C2v.C1 = 7.73; p < 0.0001), ITGAM (OR: C2v.C1 = 4.03; p = 0.0002), SCF (OR: C4v.C1 = 0.19; p-trend = 0.0001), and CCL11 (OR: C4v.C1 = 0.31; p-trend= 0.002) were all associated with development of cirrhosis compared to controls; these markers, together with clinical/demographics variables, improved prediction of cirrhosis from 55.7% (in clinical/demographic-only model) to 74.9% accuracy. A twelve-marker model based on CDA results further increased prediction of cirrhosis to 88.0%. While six biological pathways were found to be associated with cirrhosis, cell adhesion was the only pathway associated with cirrhosis after Bonferroni correction. In contrast to cirrhosis, DEFA-1 and ITGAM levels were inversely associated with HCC risk. Conclusions: Pending validation, these findings highlight the important role of immunological markers in predicting HCV-related cirrhosis even 11 years post-enrollment.

In vitro Screening of Herbal Medicinal Products for Their Supportive Curing Potential in the Context of SARS-CoV-2

COVID-19 herbal medicinal products may have the potential for symptom relief in nonsevere or moderate disease cases. In this in vitro study we screened the five herbal medicinal products Sinupret extract (SINx), Bronchipret thyme-ivy (BRO-TE), Bronchipret thyme-primula (BRO TP), Imupret (IMU), and Tonsipret (TOP) with regard to their potential to (i) interfere with the binding of the human angiotensin-converting enzyme 2 (ACE2) receptor with the SARS-CoV-2 spike S1 protein, (ii) modulate the release of the human defensin HBD1 and cathelicidin LL-37 from human A549 lung cells upon spike S1 protein stimulation, and (iii) modulate the release of IFN-γ from activated human peripheral blood mononuclear cells (PBMC). The effect of the extracts on the interaction of spike S1 protein and the human ACE2 receptor was measured by ELISA. The effects on the intracellular IFN-γ expression in stimulated human PBMC were measured by flow cytometry. Regulation of HBD1 and LL-37 expression and secretion was assessed in 25 d long-term cultured human lung A549 epithelial cells by RT-PCR and ELISA. IMU and BRO-TE concentration-dependently inhibited the interaction between spike S1 protein and the ACE2 receptor. SINx, TOP, and BRO-TE significantly upregulated the intracellular expression of anti-viral IFN-γ from stimulated PBMC. Cotreatment of A549 cells with IMU or BRO TP together with SARS-CoV-2 spike protein significantly upregulated mRNA expression (IMU) and release of HBD1 (IMU and BRO TP) and LL-37 (BRO TP). The in vitro screening results provide first evidence for an immune-activating potential of some of the tested herbal medicinal extracts in the context of SARS-CoV-2. Whether these could be supportive in symptom relief or curing from SARS-CoV-2 infection needs deeper understanding of the observations.

β-Defensin: An adroit saviour in teleosts

β-Defensin (BD) is an important first line innate defense molecule with potent antimicrobial and immunomodulatory activities in fish. The signatures of β-defensins are the presence of a net cationic charge and three intramolecular disulfide bonds mediated by six conserved cysteines. It consists of three exons and two introns. The signal peptide is usually conserved and sequence divergence is mostly seen in mature peptide region. The diverse amino acid sequences of matured peptide contribute to a strong positive selection and broad-spectrum antimicrobial activity. It is constitutively expressed in both mucosal as well as systemic sites. Increased expression of β-defensin was mostly reported in bacterial and viral infections in fish. Its role during parasitic and fungal infections is yet to be investigated. β-Defensin isoforms such as BD-1, BD-2, BD-3, BD-4 and BD-5 can be witnessed even in early developmental days to different pathogenic exposure in fish. β-Defensins possess adjuvant properties to enhance antigen-specific immunity promoting both cellular and humoral immune response. It significantly reduces/increases bacterial colonization or viral copy numbers when overexpressed/knockdown. Based on its chemotactic and activating potentials, it can contribute to both innate and adaptive immune responses. With mediated expression, it can also control inflammation. It is potent governing resistance in early developmental days as well. Its expression in pituitary and testis suggests its participation in reproduction and endocrine regulation in fish. Overall, β-defensins is an important member of antimicrobial peptides (AMPs) with multifunctional role in general homeostasis and to pathogen exposure possessing tremendous therapeutic approaches.

Inhibition of SARS-CoV-2 Infection by Human Defensin HNP1 and Retrocyclin RC-101

Severe acute respiratory syndrome coronavirus (SARS-CoV)-2 is an enveloped virus responsible for the COVID-19 pandemic. The emergence of new potentially more transmissible and vaccine-resistant variants of SARS-CoV-2 is an ever-present threat. Thus, it remains essential to better understand innate immune mechanisms that can inhibit the virus. One component of the innate immune system with broad antipathogen, including antiviral, activity is a group of cationic immune peptides termed defensins. The ability of defensins to neutralize enveloped and non-enveloped viruses and to inactivate numerous bacterial toxins correlate with their ability to promote the unfolding of proteins with high conformational plasticity. We found that human neutrophil α-defensin HNP1 binds to SARS-CoV-2 Spike protein with submicromolar affinity that is more than 20 fold stronger than its binding to serum albumin. As such, HNP1, as well as a θ-defensin retrocyclin RC-101, both interfere with Spike-mediated membrane fusion, Spike-pseudotyped lentivirus infection, and authentic SARS-CoV-2 infection in cell culture. These effects correlate with the abilities of the defensins to destabilize and precipitate Spike protein and inhibit the interaction of Spike with the ACE2 receptor. Serum reduces the anti-SARS-CoV-2 activity of HNP1, though at high concentrations, HNP1 was able to inactivate the virus even in the presence of serum. Overall, our results suggest that defensins can negatively affect the native conformation of SARS-CoV-2 Spike, and that α- and θ-defensins may be valuable tools in developing SARS-CoV-2 infection prevention strategies.

Efficacy of defensins as neutralizing agents against the deadly SARS-CoV-2

SARS-CoV-2 infection causes asymptomatic to severe human respiratory diseases. Vaccinations are effective only to a certain extent, and the disease recurs with milder symptoms even after booster doses. Hence, we hypothesize that antiviral therapy in conjunction with vaccination is the need of the hour for containing the disease. SARS-CoV-2 enters the host cell through interaction between viral spike (S) protein and human Angiotensin II converting enzyme2 (ACE2). So, any S-protein neutralizing molecule could be a potential antiviral moiety. The interaction-interface architecture indicates that cationic peptides effectively bind to anionic interface residues of S protein-receptor binding domain (S-RBD). Subsequently, we adopted molecular docking and simulation approaches to examine the binding affinity of cationic human α and β defensins, HNP1 and HBD2 with S-RBD. We observed strong hydrogen bonds, electrostatic, salt bridge, and hydrophobic interactions between these defensins and S-RBD with binding energy (BE) of -10.7 kcal/mol. Interestingly, defensins from Zea mays (ZmD32), Solanum lycopersicum (TPP3), and Sorghum bicolor (DEF1_SORBI) exhibited approximately similar BE of -11.1 kcal/mol, -11.9 kcal/mol, and -12.6 kcal/mol respectively, comparable to ACE2 (BE= -11.9 kcal/mol). Molecular dynamics simulation of S-RBD complexes formed with HBD2, ZmD32 and TPP3, showed stable associations for 100 ns. Results of in-silico studies demonstrated higher binding affinity of more positively-charged peptides with S-RBD, suggesting the potential of plant defensins to block ACE2 binding of S-RBD. These results warrant experimental validation. However these findings indicate the usefulness of plant defensin homologues as neutralizing antiviral agents for use as ideal prophylactic and therapeutic drugs for COVID-19.Communicated by Ramaswamy H. Sarma.

Age-Related Expression of IFN-λ1 Versus IFN-I and Beta-Defensins in the Nasopharynx of SARS-CoV-2-Infected Individuals

SARS-CoV-2 coronavirus infection induces heterogeneous symptoms, ranging from asymptomatic to lethal forms. Severe forms usually occur in the elderly and/or individuals with comorbidities. Children generally remain asymptomatic to primary infection, suggesting that they may have an effective local innate immune response. IFN-I and -III have non-redundant protective roles against SARS-CoV-2, although sometimes damaging the host. The expression and role of anti-viral peptides during SARS-CoV-2 infection have thus far been little studied. We aimed to identify the innate immune molecules present at the SARS-CoV-2 entry point. We analyzed the mRNA levels of type I (IFN-α and -β) and type III (IFN-λ1-3) interferons and selected antiviral peptides (i.e., β-defensins 1-3, α-defensins [HNP1-3, HD5] pentraxin-3, surfactant protein D, the cathelicidin LL-37 and interleukin-26) in nasopharyngeal swabs from 226 individuals of various ages, either infected with SARS-CoV-2 (symptomatic or asymptomatic) or negative for the virus. We observed that infection induced selective upregulation of IFN-λ1 expression in pediatric subjects (≤15 years), whereas IFN-α, IFN-β, IFN-λ2/λ3, and β-defensin 1-3 expression was unaffected. Conversely, infection triggered upregulation of IFN-α, IFN-β, IFN-λ2/λ3, and β-defensin 1-3 mRNA expression in adults (15-65 years) and the elderly (≥ 65 years), but without modulation of IFN-λ1. The expression of these innate molecules was not associated with gender or symptoms. Expression of the interferon-stimulated genes IFITM1 and IFITM3 was upregulated in SARS-CoV-2-positive subjects and reached similar levels in the three age groups. Finally, age-related differences in nasopharyngeal innate immunity were also observed in SARS-CoV-2-negative subjects. This study shows that the expression patterns of IFN-I/-III and certain anti-viral molecules in the nasopharyngeal mucosa of SARS-CoV-2-infected subjects differ with age and suggests that susceptibility to SARS-CoV-2 may be related to intrinsic differences in the nature of mucosal anti-viral innate immunity.

Human beta-defensins 2 and 4 are dysregulated in patients with coronavirus disease 19

Antimicrobial peptides (AMPs) have recently been proposed as significant immunological factors involved in pathogenesis of coronavirus disease 19 (COVID-19). Human β-defensins (hBDs) are among these AMPs, but the evidence is not well detailed. Therefore, this case-control study analyzed levels of hBD1, hBD2, hBD3 and hBD4 in serum of 103 patients with severe COVID-19 and 105 healthy controls. Most patients were older than 45 years (80.6%), and more than 50% suffered from chronic diseases (cardiovascular and diabetes). Results revealed that median levels of hBD1 and hBD3 did not show significant differences between patients and controls. On the contrary, HBD2 levels were significantly decreased in patients compared to controls (1036 vs. 1289 ng/L; p < 0.001), while HBD4 levels were significantly increased (4.04 vs. 2.43 ng/L; p < 0.001). Receiver operating characteristic curve analysis demonstrated the predictive significance of hBD2 (area under the curve [AUC] = 0.795; 95% confidence interval [CI] = 0.729–0.861; p < 0.001) and hBD4 (AUC = 0.816; 95% CI = 0.756–0.876; p < 0.001) in discriminating between COVID-19 patients and controls. Logistic regression analysis (adjusted for age, gender and body mass index) confirmed the significance of hBD2 (odds ratio [OR] = 0.996; corrected p = 0.004) and hBD4 (OR = 4.948; corrected p < 0.001) in susceptibility to COVID-19. In conclusion, the study indicated that hBD2 showed low levels in serum of patients infected with severe COVID-19, while hBD4 showed elevated levels. These differences in HBDs were not influenced by age, gender, body mass index, or chronic disease.

The Role of Obesity in the Immunopathogenesis of COVID-19 Respiratory Disease and Critical Illness

Coronavirus disease (COVID-19), the clinical syndrome caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is currently a global health pandemic with substantial morbidity and mortality. COVID-19 has cast a shadow on nearly every aspect of society, straining health systems and economies across the world. Although it is widely accepted that a close relationship exists between obesity, cardiovascular disease, and metabolic disorders on infection, we are only beginning to understand ways in which the immunological sequelae of obesity functions as a predisposing factor related to poor clinical outcomes in COVID-19. As both the innate and adaptive immune systems are each primed by obesity, the alteration of key pathways results in both an immunosuppressed and hyperinflammatory state. The present review will discuss the cellular and molecular immunology of obesity in the context of its role as a risk factor for severe COVID-19, discuss the role of cytokine storm, and draw parallels to prior viral epidemics such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and 2009 H1N1.

Human Defensins Inhibit SARS-CoV-2 Infection by Blocking Viral Entry

Innate immunity during acute infection plays a critical role in the disease severity of severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS), and is likely to contribute to COVID-19 disease outcomes. Defensins are highly abundant innate immune factors in neutrophils and epithelial cells, including intestinal Paneth cells, and exhibit antimicrobial and immune-modulatory activities. In this study, we investigated the effects of human α- and β-defensins and RC101, a θ-defensin analog, on SARS-CoV-2 infection. We found that human neutrophil peptides (HNPs) 1-3, human defensin (HD) 5 and RC101 exhibited potent antiviral activity against pseudotyped viruses expressing SARS-CoV-2 spike proteins. HNP4 and HD6 had weak anti-SARS-CoV-2 activity, whereas human β-defensins (HBD2, HBD5 and HBD6) had no effect. HNP1, HD5 and RC101 also inhibited infection by replication-competent SARS-CoV-2 viruses and SARS-CoV-2 variants. Pretreatment of cells with HNP1, HD5 or RC101 provided some protection against viral infection. These defensins did not have an effect when provided post-infection, indicating their effect was directed towards viral entry. Indeed, HNP1 inhibited viral fusion but not the binding of the spike receptor-binding domain to hACE2. The anti-SARS-CoV-2 effect of defensins was influenced by the structure of the peptides, as linear unstructured forms of HNP1 and HD5 lost their antiviral function. Pro-HD5, the precursor of HD5, did not block infection by SARS-CoV-2. High virus titers overcame the effect of low levels of HNP1, indicating that defensins act on the virion. HNP1, HD5 and RC101 also blocked viral infection of intestinal and lung epithelial cells. The protective effects of defensins reported here suggest that they may be useful additives to the antivirus arsenal and should be thoroughly studied.

Antimicrobial Peptides Derived From Insects Offer a Novel Therapeutic Option to Combat Biofilm: A Review

Biofilms form a complex layer with defined structures, that attach on biotic or abiotic surfaces, are tough to eradicate and tend to cause some resistance against most antibiotics. Several studies confirmed that biofilm-producing bacteria exhibit higher resistance compared to the planktonic form of the same species. Antibiotic resistance factors are well understood in planktonic bacteria which is not so in case of biofilm producing forms. This may be due to the lack of available drugs with known resistance mechanisms for biofilms. Existing antibiotics cannot eradicate most biofilms, especially of ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). Insects produce complex and diverse set of chemicals for survival and defense. Antimicrobial peptides (AMPs), produced by most insects, generally have a broad spectrum of activity and the potential to bypass the resistance mechanisms of classical antibiotics. Besides, AMPs may well act synergistically with classical antibiotics for a double-pronged attack on infections. Thus, AMPs could be promising alternatives to overcome medically important biofilms, decrease the possibility of acquired resistance and treatment of multidrug-resistant pathogens including ESKAPE. The present review focuses on insect-derived AMPs with special reference to anti-biofilm-based strategies. It covers the AMP composition, pathways and mechanisms of action, the formation of biofilms, impact of biofilms on human diseases, current strategies as well as therapeutic options to combat biofilm with antimicrobial peptides from insects. In addition, the review also illustrates the importance of bioinformatics tools and molecular docking studies to boost the importance of select bioactive peptides those can be developed as drugs, as well as suggestions for further basic and clinical research.

Role of Atypical Chemokines and Chemokine Receptors Pathways in the Pathogenesis of COPD

Chronic obstructive pulmonary disease (COPD) represents a heightened inflammatory response in the lung generally resulting from tobacco smoking-induced recruitment and activation of inflammatory cells and/or activation of lower airway structural cells. Several mediators can modulate activation and recruitment of these cells, particularly those belonging to the chemokines (conventional and atypical) family. There is emerging evidence for complex roles of atypical chemokines and their receptors (such as high mobility group box 1 (HMGB1), antimicrobial peptides, receptor for advanced glycosylation end products (RAGE) or toll-like receptors (TLRs)) in the pathogenesis of COPD, both in the stable disease and during exacerbations. Modulators of these pathways represent potential novel therapies for COPD and many are now in preclinical development. Inhibition of only a single atypical chemokine or receptor may not block inflammatory processes because there is redundancy in this network. However, there are many animal studies that encourage studies for modulating the atypical chemokine network in COPD. Thus, few pharmaceutical companies maintain a significant interest in developing agents that target these molecules as potential antiinflammatory drugs. Antibody-based (biological) and small molecule drug (SMD)-based therapies targeting atypical chemokines and/or their receptors are mostly at the preclinical stage and their progression to clinical trials is eagerly awaited. These agents will most likely enhance our knowledge about the role of atypical chemokines in COPD pathophysiology and thereby improve COPD management.

Promising role of defensins peptides as therapeutics to combat against viral infection

Antimicrobial peptides (AMPs) are ubiquitously present small peptides, which play a critical function in the innate immune system. The defensin class of AMPs represented an evolutionarily ancient family containing cationic cysteine residue and frequently expressed in epithelial or neutrophils cells. It plays myriad functions in host innate immune responses against various infection. Defensin has a broad spectrum of antimicrobial activities, including anti-bacteria, anti-viruses (AVPs), anti-fungi, anti-cancers, and also overcoming bacterial drug resistance. In this review, we compiled the progress on defensin, particularly incorporating the mechanism of action, their application as an antiviral agent, prospects in different areas, and limitations to be solved as an antiviral peptide. Defensins were explored, in particular, their capacity to stimulate innate and adaptive immunity by trigging as anti-coronavirus (COVID-19) peptides. The present review summarised its immunomodulatory and immunoenhancing properties and predominantly focused on its promising therapeutic adjuvant choices for combat against viral infection.

Antimicrobial peptides and other peptide-like therapeutics as promising candidates to combat SARS-CoV-2

Introduction: There are currently no specific drugs and universal vaccines for Coronavirus disease 2019 (COVID-19), hence urgent effective measures are needed to discover and develop therapeutic agents. Applying peptide therapeutics and their related compounds is a promising strategy to achieve this goal. This review is written based on the literature search using several databases, previous studies, scientific reports, our current knowledge about the antimicrobial peptides (AMPs), and our personal analyses on the potential of the antiviral peptides for the treatment of COVID-19.

Areas covered: In this review, we begin with a brief description of SARS-CoV2 followed by a comprehensive description of antiviral peptides (AVPs) including natural and synthetic AMPs or AVPs and peptidomimetics. Subsequently, the structural features, mechanisms of action, limitations, and therapeutic applications of these peptides are explained.

Expert opinion: Regarding the lack and the limitations of drugs against COVID-19, AMPs, AVPs, and other peptide-like compounds such as peptidomimetics have captured the attention of researchers due to their potential antiviral activities. Some of these compounds comprise unique properties and have demonstrated the potential to fight SARS-CoV2, particularly melittin, lactoferrin, enfuvirtide, and rupintrivir that have the potential to enter animal and clinical trials for the treatment of COVID-19.

The Expanding Role of Biomarkers in Diagnosing Infection in Total Joint Arthroplasty: A Review of Current Literature

Consistent diagnosis of periprosthetic infection in total joint arthroplasty continues to elude the orthopedic surgeon because no gold standard test exists. Therefore clinicians must rely on a combination of tests to help aid the diagnosis. The expanding role of biomarkers has shown promising results to more accurately diagnose an infection when combined with clinical suspicion and bacterial culture testing. This paper reviews the diagnostic capabilities of the most current serum and synovial biomarkers as well as next generation sequencing in the setting of periprosthetic joint infection. Future research and high-powered studies will be necessary to determine sensitivity and specificity of each biomarker.

Brilacidin Demonstrates Inhibition of SARS-CoV-2 in Cell Culture

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the newly emergent causative agent of coronavirus disease-19 (COVID-19), has resulted in more than two million deaths worldwide since it was first detected in 2019. There is a critical global need for therapeutic intervention strategies that can be deployed to safely treat COVID-19 disease and reduce associated morbidity and mortality. Increasing evidence shows that both natural and synthetic antimicrobial peptides (AMPs), also referred to as Host Defense Proteins/Peptides (HDPs), can inhibit SARS-CoV-2, paving the way for the potential clinical use of these molecules as therapeutic options. In this manuscript, we describe the potent antiviral activity exerted by brilacidin-a de novo designed synthetic small molecule that captures the biological properties of HDPs-on SARS-CoV-2 in a human lung cell line (Calu-3) and a monkey cell line (Vero). These data suggest that SARS-CoV-2 inhibition in these cell culture models is likely to be a result of the impact of brilacidin on viral entry and its disruption of viral integrity. Brilacidin demonstrated synergistic antiviral activity when combined with remdesivir. Collectively, our data demonstrate that brilacidin exerts potent inhibition of SARS-CoV-2 against different strains of the virus in cell culture.

Distinct Antiviral Properties of Two Different Bacterial Lysates

Oral bacterial lysates (OBLs) can reduce the frequency and severity of recurrent respiratory tract infections in children from viral and bacterial origins. OBL-induced early innate immune reaction was already shown, but the specific features of different OBLs have never been studied and compared. A study was conducted to assess in vitro the protective effects on rhinovirus- (RV-) infected human bronchial epithelial cells (BECs) of two slightly different OBLs: OM-85 and Pulmonarom. Furthermore, since immune cells represent the key arm for antiviral defence, the capacity of these OBLs to induce selected cytokine production in mouse bone marrow-derived DCs (BMDCs) was also evaluated. Although different OBLs may share some mechanisms to protect host cells from virus infection, some product-specific antimicrobial activities were observed on RV-infected human BECs and mouse BMDCs. These results are consistent with a product-specific response possibly triggered by different pathogen-associated molecular patterns (PAMPs) contained in OBLs.

Cooperative Function of LL-37 and HNP1 Protects Mammalian Cell Membranes from Lysis

LL-37, cleaved from human cathelicidin, and human neutrophil peptide-1 (HNP1) from the defensin family are antimicrobial peptides that are occasionally co-released from neutrophils, which synergistically kill bacteria. We report that this couple presents another type of cooperativity against host eukaryotic cells, in which they antagonistically minimize cytotoxicity by protecting membranes from lysis. Our results describe the potential of the LL-37/HNP1 cooperativity that switches from membrane-destructive to membrane-protective functions, depending on whether the target is an enemy or a host.

Antimicrobial Peptides of Salmonid Fish: From Form to Function

Antimicrobial peptides (AMPs) are small, usually cationic, and amphiphilic molecules that play a crucial role in molecular and cellular host defense against pathogens, tissue damage, and infection. AMPs are present in all metazoans and several have been discovered in teleosts. Some teleosts, such as salmonids, have undergone whole genome duplication events and retained a diverse AMP repertoire. Salmonid AMPs have also been shown to possess diverse and potent antibacterial, antiviral, and antiparasitic activity and are induced by a variety of factors, including dietary components and specific molecules also known as pathogen-associated molecular patterns (PAMPs), which may activate downstream signals to initiate transcription of AMP genes. Moreover, a multitude of cell lines have been established from various salmonid species, making it possible to study host-pathogen interactions in vitro, and several of these cell lines have been shown to express various AMPs. In this review, the structure, function, transcriptional regulation, and immunomodulatory role of salmonid AMPs are highlighted in health and disease. It is important to characterize and understand how salmonid AMPs function as this may lead to a better understanding of host-pathogen interactions with implications for aquaculture and medicine.

Amino acid sequence associated with bacteriophage recombination site helps to reveal genes potentially acquired through horizontal gene transfer

Background

Horizontal gene transfer, i.e. the acquisition of genetic material from nonparent organism, is considered an important force driving species evolution. Many cases of horizontal gene transfer from prokaryotes to eukaryotes have been registered, but no transfer mechanism has been deciphered so far, although viruses were proposed as possible vectors in several studies. In agreement with this idea, in our previous study we discovered that in two eukaryotic proteins bacteriophage recombination site (AttP) was adjacent to the regions originating via horizontal gene transfer. In one of those cases AttP site was present inside the introns of cysteine-rich repeats. In the present study we aimed to apply computational tools for finding multiple horizontal gene transfer events in large genome databases. For that purpose we used a sequence of cysteine-rich repeats to identify genes potentially acquired through horizontal transfer.

Results

HMMER remote similarity search significantly detected 382 proteins containing cysteine-rich repeats. All of them, except 8 sequences, belong to eukaryotes. In 124 proteins the presence of conserved structural domains was predicted. In spite of the fact that cysteine-rich repeats are found almost exclusively in eukaryotic proteins, many predicted domains are most common for prokaryotes or bacteriophages. Ninety-eight proteins out of 124 contain typical prokaryotic domains. In those cases proteins were considered as potentially originating via horizontal transfer. In addition, HHblits search revealed that two domains of the same fungal protein, Glycoside hydrolase and Peptidase M15, have high similarity with proteins of two different prokaryotic species, hinting at independent horizontal gene transfer events.

Conclusions

Cysteine-rich repeats in eukaryotic proteins are usually accompanied by conserved domains typical for prokaryotes or bacteriophages. These proteins, containing both cysteine-rich repeats, and characteristic prokaryotic domains, might represent multiple independent horizontal gene transfer events from prokaryotes to eukaryotes. We believe that the presence of bacteriophage recombination site inside cysteine-rich repeat coding sequence may facilitate horizontal genes transfer. Thus computational approach, described in the present study, can help finding multiple sequences originated from horizontal transfer in eukaryotic genomes.

Antiviral Activities of Human Host Defense Peptides

Peptides with broad-spectrum antimicrobial activity are found widely expressed throughout nature. As they participate in a number of different aspects of innate immunity in mammals, they have been termed Host Defense Peptides (HDPs). Due to their common structural features, including an amphipathic structure and cationic charge, they have been widely shown to interact with and disrupt microbial membranes. Thus, it is not surprising that human HDPs have activity against enveloped viruses as well as bacteria and fungi. However, these peptides also exhibit activity against a wide range of non-enveloped viruses as well, acting at a number of different steps in viral infection. This review focuses on the activity of human host defense peptides, including alpha- and beta-defensins and the sole human cathelicidin, LL-37, against both enveloped and non-enveloped viruses. The broad spectrum of antiviral activity of these peptides, both in vitro and in vivo suggest that they play an important role in the innate antiviral defense against viral infections. Furthermore, the literature suggests that they may be developed into antiviral therapeutic agents.

Associations between Bovine β-Defensin 4 Genotypes and Production Traits of Polish Holstein-Friesian Dairy Cattle

Simple Summary

Mastitis negatively affects dairy cattle, causing inferior milk quality and premature animal culling, which leads to economic losses. Therefore, selection based on genetic markers (i.g., marker-assisted selection) should also include functional traits with low heritability, such as resistance to udder inflammation. Single nucleotide polymorphisms (SNPs) identified in genes involved in the immune system, such as defensins with antibacterial properties, could be valuable markers. We chose two SNPs within the bovine neutrophil beta-defensin 4 (BNBD4) gene analyzed in a previous study related to milk production and udder health. Since these SNPs are located very close to each other in the gene intron, it is useful to analyze their association with production traits as a combined genotype. The results showed that these genotypes are indeed associated with productivity, as well as functional traits (milk, fat, and protein yields, fat, protein, lactose, and dry matter contents, and somatic cell count). The differences between the results based on the phenotypic data and the breeding values of studied traits may confirm the results of simulation studies that indicate a high rate of false-positives in genome-wide association study (GWAS) based on classically calculated estimated breeding values (EBVs) using best linear unbiased prediction (BLUP) methodology.

Abstract

This study analyzed the associations between two single-nucleotide polymorphisms (C2239T and A1674C), used together as a genotype located in BNBD4, and milk traits and breeding values of productivity traits of Polish Holstein-Friesian dairy cows. The research was carried out on 322 cows, with 7070 milk parameter and somatic cell count records in daily milking, as well as 897 records covering data on whole lactations, and 2209 breeding value records for productivity traits. The DMU statistical package with a one-trait repeatability test-day animal model was used to estimate the associations. The differences between the genotype effects were analyzed using Duncan’s post-hoc tests. The CC/AA and CT/AC genotypes had the highest frequencies (0.62 and 0.23, respectively). For use in marker-assisted selection, the CC/AC genotype is the most promising as an indicator of high-yielding cows potentially resistant to mastitis, because it was associated with the lowest somatic cell count (SCC), highest milk, fat, and protein yields in daily milking, as well as with milk yield in the whole lactation. The studied genotypes were also related to the breeding values of all the investigated production traits. However, some simulation studies have indicated a high rate of false-positives in GWAS based on classically calculated EBVs.

Human Antimicrobial Peptides as Therapeutics for Viral Infections

Successful in vivo infection following pathogen entry requires the evasion and subversion of multiple immunological barriers. Antimicrobial peptides (AMPs) are one of the first immune pathways upregulated during infection by multiple pathogens, in multiple organs in vivo. In humans, there are many classes of AMPs exhibiting broad antimicrobial activities, with defensins and the human cathelicidin LL-37 being the best studied examples. Whereas historically the efficacy and therapeutic potential of AMPs against bacterial infection has been the primary focus of research, recent studies have begun to elucidate the antiviral properties of AMPs as well as their role in regulation of inflammation and chemoattraction. AMPs as therapeutic tools seem especially promising against emerging infectious viral pathogens for which no approved vaccines or treatments are currently available, such as dengue virus (DENV) and Zika virus (ZIKV). In this review, we summarize recent studies elucidating the efficacy and diverse mechanisms of action of various classes of AMPs against multiple viral pathogens, as well as the potential use of human AMPs in novel antiviral therapeutic strategies.

A β-defensin gene of Trachinotus ovatus might be involved in the antimicrobial and antiviral immune response

Defensins are a group of small cationic and cysteine-rich peptides that are important components of the innate immune system. However, studies on defensins in teleosts are very limited, particularly studies on defensin functions through in vivo assays. In this study, we cloned and identified one β-defensin (TroBD) the golden pompano, Trachinotus ovatus, and analyzed the functions of TroBD in both in vivo and in vitro assays. TroBD is composed of 63 amino acids and shares high sequence identities (27.27-98.41%) with known β-defensins of other teleosts. The protein has a signature motif of six conserved cysteine residues within the mature peptide. The expression of TroBD was most abundant in the head kidney and spleen and was significantly upregulated following infection by Vibrio harveyi and viral nervous necrosis virus (VNNV). Purified recombinant TroBD (rTroBD) inhibited the growth of V. harveyi, and its antimicrobial activity was influenced by salt concentration. TroBD was found to have a chemotactic effect on macrophages in vitro. The results of an in vivo study demonstrated that TroBD overexpression/knockdown in T. ovatus significantly reduced/increased bacterial colonization or viral copy numbers in tissues. Taken together, these results indicate that TroBD plays a significant role in both antibacterial and antiviral immunity and provide new avenues for protection against pathogen infection in the aquaculture industry.

Features of a novel protein, rusticalin, from the ascidian Styela rustica reveal ancestral horizontal gene transfer event

Background

The transfer of genetic material from non-parent organisms is called horizontal gene transfer (HGT). One of the most conclusive cases of HGT in metazoans was previously described for the cellulose synthase gene in ascidians.

Results

In this study we identified a new protein, rusticalin, from the ascidian Styela rustica and presented evidence for its likely origin by HGT. Discernible homologues of rusticalin were found in placozoans, coral, and basal Chordates. Rusticalin was predicted to consist of two distinct regions, an N-terminal domain and a C-terminal domain. The N-terminal domain comprises two cysteine-rich repeats and shows remote similarity to the tick carboxypeptidase inhibitor. The C-terminal domain shares significant sequence similarity with bacterial MD peptidases and bacteriophage A500 L-alanyl-D-glutamate peptidase. A possible transfer of the C-terminal domain by bacteriophage was confirmed by an analysis of noncoding sequences of C. intestinalis rusticalin-like gene, which was found to contain a sequence similar to the bacteriophage A500 recombination site. Moreover, a sequence similar to the bacteriophage recombination site was found to be adjacent to the cellulose synthase catalytic subunit gene in the genome of Streptomices sp., the donor of ascidian cellulose synthase.

Conclusions

The C-terminal domain of rusticalin and rusticalin-like proteins is likely to be horizontally transferred by the bacteriophage A500. A common mechanism involving bacteriophage mediated gene transfer can be proposed for at least two HGT events in ascidians.

The Transcriptional Response of Aedes aegypti with Variable Extrinsic Incubation Periods for Dengue Virus

Dengue fever is the most prevalent arboviral disease globally. Dengue virus is transmitted primarily by the Aedes aegypti mosquito. One measure of the mosquito’s efficiency as a vector is the extrinsic incubation period (EIP), which is the time between the ingestion of viremic blood and the emergence of virions in the saliva. The longer it takes virus to infect the midgut and traverse to the saliva, the fewer opportunities the mosquito will have to transmit the pathogen over its lifetime. We have shown previously that EIP for dengue virus is highly heritable and that it is negatively correlated with vector lifespan. Here, we examined the transcriptional profiles for mosquitoes that varied in their EIP phenotype and identified pathways associated with either short or long EIP. We found that mosquitoes with short EIP have less active immune responses but higher levels of protein translation and calcium ion homeostasis and that mosquitoes with longer EIP may have slower metabolism. These findings indicate a complex interplay between calcium ion distribution, ribosome biogenesis, and metabolism and reveal potential pathways that could be modified to slow the rate of viral progression and hence limit lifetime transmission capability.

The Mouse Papillomavirus Infection Model

The mouse papillomavirus (MmuPV1) was first reported in 2011 and has since become a powerful research tool. Through collective efforts from different groups, significant progress has been made in the understanding of molecular, virological, and immunological mechanisms of MmuPV1 infections in both immunocompromised and immunocompetent hosts. This mouse papillomavirus provides, for the first time, the opportunity to study papillomavirus infections in the context of a small common laboratory animal for which abundant reagents are available and for which many strains exist. The model is a major step forward in the study of papillomavirus disease and pathology. In this review, we summarize studies using MmuPV1 over the past six years and share our perspectives on the value of this unique model system. Specifically, we discuss viral pathogenesis in cutaneous and mucosal tissues as well as in different mouse strains, immune responses to the virus, and local host-restricted factors that may be involved in MmuPV1 infections and associated disease progression.

Human Beta Defensin 2 Selectively Inhibits HIV-1 in Highly Permissive CCR6⁺CD4⁺ T Cells

Chemokine receptor type 6 (CCR6)⁺CD4⁺ T cells are preferentially infected and depleted during HIV disease progression, but are preserved in non-progressors. CCR6 is expressed on a heterogeneous population of memory CD4⁺ T cells that are critical to mucosal immunity. Preferential infection of these cells is associated, in part, with high surface expression of CCR5, CXCR4, and α4β7. In addition, CCR6⁺CD4⁺ T cells harbor elevated levels of integrated viral DNA and high levels of proliferation markers. We have previously shown that the CCR6 ligands MIP-3α and human beta defensins inhibit HIV replication. The inhibition required CCR6 and the induction of APOBEC3G. Here, we further characterize the induction of apolipoprotein B mRNA editing enzyme (APOBEC3G) by human beta defensin 2. Human beta defensin 2 rapidly induces transcriptional induction of APOBEC3G that involves extracellular signal-regulated kinases 1/2 (ERK1/2) activation and the transcription factors NFATc2, NFATc1, and IRF4. We demonstrate that human beta defensin 2 selectively protects primary CCR6⁺CD4⁺ T cells infected with HIV-1. The selective protection of CCR6⁺CD4⁺ T cell subsets may be critical in maintaining mucosal immune function and preventing disease progression.

Antiviral function of Tachyplesin I against iridovirus and nodavirus

Antimicrobial peptides (AMPs) are ubiquitously found in living organisms and are an important component in innate immune response. Tachyplesin I is a potent antimicrobial peptide isolated from the hemocytes of the horseshoe crab, Tachypleus tridentatus. Previous studies have shown that the 17-residue peptide exhibits a wide spectrum of antimicrobial activity against Gram-negative and Gram-positive bacteria, fungi, protozoa, and viruses. However, the efficiencies and defense mechanisms of the Tachyplesin I against fish viruses are still unknown. In this study, Tachyplesin I showed a key role in inhibiting the infection and replication of two kinds of newly emerging marine fish viruses, an enveloped DNA virus of Singapore grouper iridovirus (SGIV), and a non-enveloped RNA virus of viral nervous necrosis virus (RGNNV). Synthetic peptides of Tachyplesin I incubated with virus or cells before infection reduced the viral infectivity. Synthetic peptides of Tachyplesin I drastically decreased SGIV and RGNNV titers and viral gene expression. Grouper spleen (GS) and brain (GB) cells over-expressing Tachyplesin I (GS/pcDNA3.1-flag-Tac I and GB/pcDNA3.1-flag-Tac I) support the inhibition of viral infection. Tachyplesin I activated type I IFN and Interferon-sensitive response element (ISRE) in vitro. The promoter activity of IFN-β and ISRE were significantly up-regulated in cells transfected with pcDNA3.1-flag-Tac I after infection with SGIV and VNNV. These results suggest that Tachyplesin I is importantly involved in host immune responses to invasion of viral pathogens.

The vaginal microbiota, host defence and reproductive physiology

The interaction between the human host and the vaginal microbiota is highly dynamic. Major changes in the vaginal physiology and microbiota over a woman's lifetime are largely shaped by transitional periods such as puberty, menopause and pregnancy, while daily fluctuations in microbial composition observed through culture-independent studies are more likely to be the results of daily life activities and behaviours. The vaginal microbiota of reproductive-aged women is largely made up of at least five different community state types. Four of these community state types are dominated by lactic-acid producing Lactobacillus spp. while the fifth is commonly composed of anaerobes and strict anaerobes and is sometimes associated with vaginal symptoms. The production of lactic acid has been associated with contributing to the overall health of the vagina due to its direct and indirect effects on pathogens and host defence. Some species associated with non-Lactobacillus vaginal microbiota may trigger immune responses as well as degrade the host mucosa, processes that ultimately increase susceptibility to infections and contribute to negative reproductive outcomes such as infertility and preterm birth. Further studies are needed to better understand the functional underpinnings of how the vaginal microbiota affect host physiology but also how host physiology affects the vaginal microbiota. Understanding this fine-tuned interaction is key to maintaining women's reproductive health.

A novel peptide with potent and broad-spectrum antiviral activities against multiple respiratory viruses

A safe, potent and broad-spectrum antiviral is urgently needed to combat emerging respiratory viruses. In light of the broad antiviral activity of β-defensins, we tested the antiviral activity of 11 peptides derived from mouse β-defensin-4 and found that a short peptide, P9, exhibited potent and broad-spectrum antiviral effects against multiple respiratory viruses in vitro and in vivo, including influenza A virus H1N1, H3N2, H5N1, H7N7, H7N9, SARS-CoV and MERS-CoV. The antiviral activity of P9 was attributed to its high-affinity binding to viral glycoproteins, as well as the abundance of basic amino acids in its composition. After binding viral particles through viral surface glycoproteins, P9 entered into cells together with the viruses via endocytosis and prevented endosomal acidification, which blocked membrane fusion and subsequent viral RNA release. This study has paved the avenue for developing new prophylactic and therapeutic agents with broad-spectrum antiviral activities.

Antiviral Host Defence Peptides

The ongoing global mortality and morbidity associated with viral pathogens highlights the need for the continued development of effective, novel antiviral molecules. The antiviral activity of cationic host defence peptides is of significant interest as novel therapeutics for treating viral infection and predominantly due to their broad spectrum antiviral activity. These peptides also display powerful immunomodulatory activity and are key mediators of inflammation. Therefore, they offer a significant opportunity to inform the development of novel therapeutics for treating viral infections by either directly targeting the pathogen or by enhancing the innate immune response. In this chapter, we review the antiviral activity of cathelicidins and defensins, and examine the potential for these peptides to be used as novel antiviral agents.

Human Alpha-Defensin HNP1 Increases HIV Traversal of the Epithelial Barrier: A Potential Role in STI-Mediated Enhancement of HIV Transmission

Alpha-defensins, including human neutrophil peptides 1-3 (HNP1-3) and human defensin 5 (HD5), are elevated at the genital mucosa in individuals with sexually transmitted infections (STIs). The presence of STIs is associated with an increased risk of human immunodeficiency virus (HIV) transmission, suggesting there may be a role for defensins in early events of HIV transmission. HD5 has been demonstrated to contribute to STI-mediated increased HIV infectivity in vitro. HNPs exhibit anti-HIV activity in vitro. However, increased levels of HNPs have been associated with enhanced HIV acquisition and higher viral load in breast milk. This study found that HNP1, but not HD5, significantly disrupted epithelial integrity and promoted HIV traversal of epithelial barriers. Linear HNP1 with the same charges did not affect epithelial permeability, indicating that the observed effect of HNP1 on the epithelial barrier was structure dependent. These results suggest a role for HNP1 in STI-mediated enhancement of HIV transmission.

The Role of Cationic Polypeptides in Modulating HIV-1 Infection of the Cervicovaginal Mucosa

The mucosa and overlying fluid of the female reproductive tract (FRT) are portals for the heterosexual transmission of HIV-1. Toward the ongoing development of topically applied microbicides and mucosal vaccines against HIV-1, it is evermore important to understand how the dynamic FRT mucosa is involved in controlling transmission and infection of HIV-1. Cationic peptides and proteins are the principal innate immune effector molecules of mucosal surfaces, and interact in a combinatorial fashion to modulate HIV-1 infection of the cervix and vagina. While cationic peptides and proteins have historically been categorized as antimicrobial or have other host-benefitting roles, an increasing number of these molecules have been found to augment HIV-1 infection and potentially antagonize host defense. Complex environmental factors such as hormonal fluctuations and/or bacterial and viral co-infections provide additional challenges to both experimentation and interpretation of results. In the context of heterosexual transmission of HIV-1, this review explores how various cationic peptides and proteins participate in modulating host defense against HIV-1 of the cervicovaginal mucosa.

The chemistry and biology of theta defensins

Cyclic peptides are found in a diverse range of organisms and are characterized by their stability and role in defense. Why is only one class of cyclic peptides found in mammals? Possibly we have not looked hard enough for them, or the technologies needed to identify them are not fully developed. We also do not yet understand their intriguing biosynthesis from two separate gene products. Addressing these challenges will require the application of chemical tools and insights from other classes of cyclic peptides. Herein, we highlight recent developments in the characterization of theta defensins and describe the important role that chemistry has played in delineating their modes of action. Furthermore, we emphasize the potential of theta defensins as antimicrobial agents and scaffolds for peptide drug design.

Discovery of modulators of HIV-1 infection from the human peptidome

Kirchhoff and colleagues discuss the discovery of novel antimicrobial peptides by systematic screening of complex peptide and protein libraries that have been derived from human bodily fluids and tissues, with a focus on the isolation of endogenous agents that affect HIV-1 infection.

Almost all human proteins are subject to proteolytic degradation, which produces a broad range of peptides that have highly specific and sometimes unexpected functions. Peptide libraries that have been generated from human bodily fluids or tissues are a rich but mostly unexplored source of bioactive compounds that could be used to develop antimicrobial and immunomodulatory therapeutic agents. In this Innovation article, we describe the discovery, optimization and application of endogenous bioactive peptides from human-derived peptide libraries, with a particular focus on the isolation of endogenous inhibitors and promoters of HIV-1 infection.

Cationic host defence peptides: potential as antiviral therapeutics

There is a pressing need to develop new antiviral treatments; of the 60 drugs currently available, half are aimed at HIV-1 and the remainder target only a further six viruses. This demand has led to the emergence of possible peptide therapies, with 15 currently in clinical trials. Advancements in understanding the antiviral potential of naturally occurring host defence peptides highlights the potential of a whole new class of molecules to be considered as antiviral therapeutics. Cationic host defence peptides, such as defensins and cathelicidins, are important components of innate immunity with antimicrobial and immunomodulatory capabilities. In recent years they have also been shown to be natural, broad-spectrum antivirals against both enveloped and non-enveloped viruses, including HIV-1, influenza virus, respiratory syncytial virus and herpes simplex virus. Here we review the antiviral properties of several families of these host peptides and their potential to inform the design of novel therapeutics.

Insect antimicrobial peptides and their applications

Insects are one of the major sources of antimicrobial peptides/proteins (AMPs). Since observation of antimicrobial activity in the hemolymph of pupae from the giant silk moths Samia Cynthia and Hyalophora cecropia in 1974 and purification of first insect AMP (cecropin) from H. cecropia pupae in 1980, over 150 insect AMPs have been purified or identified. Most insect AMPs are small and cationic, and they show activities against bacteria and/or fungi, as well as some parasites and viruses. Insect AMPs can be classified into four families based on their structures or unique sequences: the α-helical peptides (cecropin and moricin), cysteine-rich peptides (insect defensin and drosomycin), proline-rich peptides (apidaecin, drosocin, and lebocin), and glycine-rich peptides/proteins (attacin and gloverin). Among insect AMPs, defensins, cecropins, proline-rich peptides, and attacins are common, while gloverins and moricins have been identified only in Lepidoptera. Most active AMPs are small peptides of 20-50 residues, which are generated from larger inactive precursor proteins or pro-proteins, but gloverins (~14 kDa) and attacins (~20 kDa) are large antimicrobial proteins. In this mini-review, we will discuss current knowledge and recent progress in several classes of insect AMPs, including insect defensins, cecropins, attacins, lebocins and other proline-rich peptides, gloverins, and moricins, with a focus on structural-functional relationships and their potential applications.

Postentry processing of recombinant adeno-associated virus type 1 and transduction of the ferret lung are altered by a factor in airway secretions

We recently created a cystic fibrosis ferret model that acquires neonatal lung infection. To develop lung gene therapies for this model, we evaluated recombinant adeno-associated virus (rAAV)-mediated gene transfer to the neonatal ferret lung. Unlike in vitro ferret airway epithelial (FAE) cells, in vivo infection of the ferret lung with rAAV1 required proteasome inhibitors to achieve efficient airway transduction. We hypothesized that differences in transduction between these two systems were because of an in vivo secreted factor that alter the transduction biology of rAAV1. Indeed, treatment of rAAV1 with ferret airway secretory fluid (ASF) strongly inhibited rAAV1, but not rAAV2, transduction of primary FAE and HeLa cells. Properties of the ASF inhibitory factor included a strong affinity for the AAV1 capsid, heat-stability, negative charge, and sensitivity to endoproteinase Glu-C. ASF-treated rAAV1 dramatically inhibited apical transduction of FAE ALI cultures (512-fold), while only reducing viral entry by 55-fold, suggesting that postentry processing of virus was influenced by the inhibitor factor. Proteasome inhibitors rescued transduction in the presence of ASF (~1600-fold) without effecting virus internalization, while proteasome inhibitors only enhanced transduction 45-fold in the absence of ASF. These findings demonstrate that a factor in lung secretions can influence intracellular processing of rAAV1 in a proteasome-dependent fashion.

Antiviral mechanisms of human defensins

Defensins are an effector component of the innate immune system with broad antimicrobial activity. Humans express two types of defensins, α- and β-defensins, which have antiviral activity against both enveloped and non-enveloped viruses. The diversity of defensin-sensitive viral species reflects a multitude of antiviral mechanisms. These include direct defensin targeting of viral envelopes, glycoproteins, and capsids in addition to inhibition of viral fusion and post-entry neutralization. Binding and modulation of host cell surface receptors and disruption of intracellular signaling by defensins can also inhibit viral replication. In addition, defensins can function as chemokines to augment and alter adaptive immune responses, revealing an indirect antiviral mechanism. Nonetheless, many questions regarding the antiviral activities of defensins remain. Although significant mechanistic data are known for α-defensins, molecular details for β-defensin inhibition are mostly lacking. Importantly, the role of defensin antiviral activity in vivo has not been addressed due to the lack of a complete defensin knockout model. Overall, the antiviral activity of defensins is well established as are the variety of mechanisms by which defensins achieve this inhibition; however, additional research is needed to fully understand the role of defensins in viral pathogenesis.

The human alpha defensin HD5 neutralizes JC polyomavirus infection by reducing endoplasmic reticulum traffic and stabilizing the viral capsid

Progressive multifocal leukoencephalopathy (PML) is a fatal disease with limited treatment options, both clinically and in the research pipeline. Potential therapies would target and neutralize its etiologic agent, JC polyomavirus (JCPyV). The innate immune response to JCPyV infection has not been studied, and little is known about the initial host response to polyomavirus infection. This study examined the ability of a human alpha defensin, HD5, to neutralize JCPyV infection in human fetal glial cells. We show that HD5, by binding to the virion, blocks infection. The JCPyV-HD5 complexes bind to and enter host cells but are reduced in their ability to reach the endoplasmic reticulum (ER), where virions are normally uncoated. Furthermore, HD5 binding to the virion stabilizes the capsid and prevents genome release. Our results show that HD5 neutralizes JCPyV infection at an early postentry step in the viral life cycle by stabilizing the viral capsid and disrupting JCPyV trafficking. This study provides a naturally occurring platform for developing antivirals to treat PML and also expands on the known capabilities of human defensins.

Identification of sociodemographic and clinical factors associated with the levels of human β-defensin-1 and human β-defensin-2 in the human milk of Han Chinese

Human milk provides infants with various immune molecules. The objective of the present study was to measure human β-defensin-1 (hBD-1) and human β-defensin-2 (hBD-2) levels in the colostrum and mature milk of healthy Han Chinese, to identify factors regulating milk hBD-1 and hBD-2 expression and to explore the potential protective effect of milk hBD-1 and hBD-2 on infants. A total of 100 mothers and their babies were recruited into the study. Sociodemographic characteristics and other factors were obtained by a questionnaire. Babies were followed up for a period of 6 months. Colostrum samples (n 100) and mature milk samples (n 82) were collected by hand expression. The hBD-1 and hBD-2 concentrations were measured by ELISA. The hBD-1 and hBD-2 levels differed in the colostrum and mature milk. In the colostrum, the concentration ranges of hBD-1 and hBD-2 were 1·04-12·81 μg/ml and 0·31-19·12 ng/ml, respectively. In mature milk, the hBD-1 and hBD-2 levels were 1·03-31·76 ng/ml and 52·65-182·29 pg/ml, respectively. Several independent factors influence their production. The multivariable analysis showed a strong association between pre-pregnancy BMI and hBD-1 levels in the colostrum (P=0·001), mode of delivery was significantly associated with hBD-2 levels in the colostrum (P=0·006) and gestational age was significantly associated with hBD-1 levels in mature milk (P= 0·010). During the first 6 months of life, the incidence rate of upper respiratory infection was found to be less in the high-colostrum hBD-1 group than in the low-colostrum hBD-1 group (χ²=4·995, P=0·025). The present study suggested that the abundance of hBD-1 in the colostrum may have a protective function against upper respiratory infection for infants younger than 6 months.

Anti-HIV activity of human defensin 5 in primary CD4+ T cells under serum-deprived conditions is a consequence of defensin-mediated cytotoxicity

BACKGROUND

We have previously shown that human defensin 5 (HD5) promotes HIV infectivity in both primary CD4+ T cells and HeLa cells expressing CD4 and CCR5. HD5 is induced in response to sexually transmitted infections (STIs) such as Chlamydia trachomatis and Neisseria gonorrhoeae, suggesting it plays a role in STI-mediated enhancement of HIV transmission. In contrast to our findings, a recent study reports that HD5 has an anti-HIV effect in primary CD4+ T cells under serum-deprived conditions. To resolve these apparently contradictory observations, we investigated experimental parameters that might contribute to contrasting effects of HD5.

RESULTS

Serum-deprived culture conditions were associated with anti-HIV activity. In contrast to the dependence of the HIV enhancing effect on HD5 structure, the anti-HIV activity in serum-deprived primary CD4+ T cells was independent of HD5 structure as the linear peptide [Abu] HD5 exhibited similar anti-HIV activity. Under serum deprived conditions, HD5 blocked CD4-receptor-independent HIV-1vsv infection before or after viral entry. We found that HD5 and its linear form induced significant cell death in primary CD4+ T cells under serum-deprived culture conditions. HD5-mediated apoptosis was observed as early as 2 h after addition of defensins to serum-deprived primary CD4+ T cells. In contrast to primary CD4+ T cells, HD5 did not induce cytotoxicity and promote HIV infectivity of HeLa-CD4-CCR5 cells under serum-deprived conditions.

CONCLUSIONS

These results indicate that under serum-deprived culture conditions HD5 is toxic for primary CD4+ T cells, warranting caution in data interpretation.

Defensins: natural component of human innate immunity

The widespread use of antibiotics has contributed to a huge increase in the number of resistant bacteria. New classes of drugs are therefore being developed of which defensins are a potential source. Defensins are a group of antimicrobial peptides found in different living organisms, involved in the first line of defense in their innate immune response against pathogens. This review summarizes the results of studies of this family of human antimicrobial peptides (AMPs). There is a special emphasis on describing the entire group and individual peptides, history of their discovery, their functions and expression sites. The results of the recent studies on the use of the biologically active peptides in human medicine are also presented. The pharmaceutical potential of human defensins cannot be ignored, especially considering their strong antimicrobial activity and properties such as low molecular weight, reduced immunogenicity, broad activity spectrum and resistance to proteolysis, but there are still many challenges and questions regarding the possibilities of their practical application.

Beyond RNAi: antiviral defense strategies in Drosophila and mosquito

Virus transmission and spread by arthropods is a major economic and public health concern. The ongoing dissemination of arthropod-borne viruses by blood-feeding insects is an important incentive to study antiviral immunity in these animals. RNA interference is a major mechanism for antiviral defense in insects, including the fruit fly Drosophila melanogaster and several vector mosquitoes. However, recent data suggest that the evolutionary conserved Toll, Imd and Jak-Stat signaling pathways also contribute to antiviral immunity. Moreover, symbionts, such as the intracellular bacterium Wolbachia and the gut microflora, influence the course of virus infection in insects. These results add an additional level of complexity to antiviral immunity, but also provide novel opportunities to control the spread of arboviruses. In this review, we provide an overview of the current knowledge and recent developments in antiviral immunity in Dipteran insects, with a focus on non-RNAi mediated inducible responses.