Dual role of alpha-defensin-1 in anti-HIV-1 innate immunity

Brilacidin, a Non-Peptide Defensin-Mimetic Molecule, Inhibits SARS-CoV-2 Infection by Blocking Viral Entry

Brilacidin (PMX-30063), a non-peptide defensin-mimetic small molecule, inhibits SARS-CoV-2 viral infection but the anti-viral mechanism is not defined. Here we determined its effect on the specific step of the viral life cycle. Brilacidin blocked SARS-CoV-2 infection but had no effect after viral entry. Brilacidin inhibited pseudotyped SARS-CoV-2 viruses expressing spike proteins from the P.1 Brazil strain and the B.1.1.7 UK strain. Brilacidin affected viral attachment in hACE2-dependent and independent manners depending on the concentrations. The inhibitory effect on viral entry was not mediated through blocking the binding of either the spike receptor-binding domain or the spike S1 protein to hACE2 proteins. Taken together, brilacidin inhibits SARS-CoV-2 infection by blocking viral entry and is active against SARS-CoV-2 variants.

Systems biology applications to study mechanisms of human immunodeficiency virus latency and reactivation

Eradication of human immunodeficiency virus (HIV) in infected individuals is currently not possible because of the presence of the persistent cellular reservoir of latent infection. The identification of HIV latency biomarkers and a better understanding of the molecular mechanisms contributing to regulation of HIV expression might provide essential tools to eliminate these latently infected cells. This review aims at summarizing gene expression profiling and systems biology applications to studies of HIV latency and eradication. Studies comparing gene expression in latently infected and uninfected cells identify candidate latency biomarkers and novel mechanisms of latency control. Studies that profiled gene expression changes induced by existing latency reversing agents (LRAs) highlight uniting themes driving HIV reactivation and novel mechanisms that contribute to regulation of HIV expression by different LRAs. Among the reviewed gene expression studies, the common approaches included identification of differentially expressed genes and gene functional category assessment. Integration of transcriptomic data with other biological data types is presently scarce, and the field would benefit from increased adoption of these methods in future studies. In addition, designing prospective studies that use the same methods of data acquisition and statistical analyses will facilitate a more reliable identification of latency biomarkers using different model systems and the comparison of the effects of different LRAs on host factors with a role in HIV reactivation. The results from such studies would have the potential to significantly impact the process by which candidate drugs are selected and combined for future evaluations and advancement to clinical trials.

Interactions between human immunodeficiency virus type 1 and polymorphonuclear neutrophils

Polymorphonuclear neutrophils (PMN) are the most abundant circulating leukocytes. They represent a first line of innate immunity against a large panel of microbial pathogens, pending development of specific immune responses. The role of PMN in human immunodeficiency virus type 1 (HIV-1) disease has mainly been investigated from the point of view of the increased susceptibility of HIV-1-infected patients to bacterial and fungal infections. However, it is now clear that the relationship between PMN and HIV-1 is far more complex. This review examines both the beneficial and the detrimental effects of PMN during HIV infection.

Neisseria gonorrhoeae-induced human defensins 5 and 6 increase HIV infectivity: role in enhanced transmission

Sexually transmitted infections (STIs) increase the likelihood of HIV transmission. Defensins are part of the innate mucosal immune response to STIs and therefore we investigated their role in HIV infection. We found that human defensins 5 and 6 (HD5 and HD6) promoted HIV infection, and this effect was primarily during viral entry. Enhancement was seen with primary viral isolates in primary CD4(+) T cells and the effect was more pronounced with R5 virus compared with X4 virus. HD5 and HD6 promoted HIV reporter viruses pseudotyped with vesicular stomatitis virus and murine leukemia virus envelopes, indicating that defensin-mediated enhancement was not dependent on CD4 and coreceptors. Enhancement of HIV by HD5 and HD6 was influenced by the structure of the peptides, as loss of the intramolecular cysteine bonds was associated with loss of the HIV-enhancing effect. Pro-HD5, the precursor and intracellular form of HD5, also exhibited HIV-enhancing effect. Using a cervicovaginal tissue culture system, we found that expression of HD5 and HD6 was induced in response to Neisseria gonorrhoeae (GC, for gonococcus) infection and that conditioned medium from GC-exposed cervicovaginal epithelial cells with elevated levels of HD5 also enhanced HIV infection. Introduction of small interfering RNAs for HD5 or HD6 abolished the HIV-enhancing effect mediated by GC. Thus, the induction of these defensins in the mucosa in the setting of GC infection could facilitate HIV infection. Furthermore, this study demonstrates the complexity of defensins as innate immune mediators in HIV transmission and warrants further investigation of the mechanism by which defensins modulate HIV infection.

Leukotriene B4 triggers the in vitro and in vivo release of potent antimicrobial agents

Leukotriene B(4) (LTB(4)) is a bioactive lipid derived from the metabolism of arachidonic acid. Mainly produced by polymorphonuclear leukocytes (PMN) and macrophages, LTB(4) triggers several functional responses important in host defense, including the secretion of lysosomal enzymes, the activation of NADPH oxidase activity, NO formation, and phagocytosis. We report that LTB(4), but not structural analogs thereof, stimulates primed human PMN to release molecules having potent antimicrobial activities. Exposure of bacteria (Escherichia coli and Staphylococcus aureus) or viruses (herpes simplex virus type 1 and HIV type 1) to supernatants of LTB(4)-activated PMN led to > or =90% reduction in infectivity. ELISA and mass spectroscopy analysis of proteins released from LTB(4)-activated PMN have identified several antimicrobial proteins, including alpha-defensins, cathepsin G, elastase, lysozyme C, and LL-37, that are likely to participate in the killing of microorganisms. In addition to these in vitro observations, i.v. injections of LTB(4) (50 microg/kg) to monkeys led to an increase in alpha-defensin plasmatic levels and enhanced ex vivo antimicrobial activities of plasma. These results demonstrate the ability of LTB(4) to cause the release of potent antimicrobial agents from PMN in vitro as well as in vivo and add further support to the important role of LTB(4) in host defense.

Human neutrophil defensins increase neutrophil uptake of influenza A virus and bacteria and modify virus-induced respiratory burst responses

Human neutrophil peptides (HNPs) are released from granules of neutrophils in response to various activating stimuli and they participate in the killing of bacteria and the stimulation of various inflammatory responses. HNPs also inhibit infectivity of enveloped viruses, including influenza A virus (IAV). In this study, we demonstrate that HNPs increase the uptake of IAV and bacteria by neutrophils. The dimeric HNPs also induced aggregation of IAV and bacterial particles, which may, in part, explain their ability to increase uptake. HNPs did not increase neutrophil respiratory burst responses to IAV. We have recently demonstrated direct interactions of HNPs with surfactant protein D (SP-D), another important effector of innate immunity and antimicrobial host defense. Although HNPs did not alter SP-D-dependent uptake of IAV, they counteracted the ability of SP-D to increase IAV-induced neutrophil H2O2 generation. Our studies reveal previously unappreciated functional effects of HNPs, expand our understanding of the antiviral properties of HNPs, and suggest important interactions between collectins and HNPs in the host response to viruses and bacteria.

Mechanisms of over-activated innate immune system regulation in autoimmune and neurodegenerative disorders

Reactions of innate immunity include phagocytosis, the production and activity of cytokines, chemokines, and adhesion molecules, the killing of infected or changed cells by NK cells and complement activated by natural lectins, and the cytokine-dependent resistance of leukocytes to viral infection. All these mechanisms maintain innate immunity. Deficiency in this immunity is sometimes accompanied by frequent bacterial and viral infections. When innate immunity is permanently stimulated and the intensity of the reactions is stronger, these mechanisms may be directed against the host and subsequently stimulate acquired immunity (antibody and cellular immunity). A higher production of cytokines, oxidative stress, and a high production of NO accompany autoimmunity and neurodegeneration. The possible participation of innate immune receptors, cytokines, and other factors in the development of autoimmune and neurodegenerative diseases is discussed. The importance and possible role of blood-derived microglial cells in the prevention or elimination of amyloid deposits and plaque formation is described. A possible regulatory system, based on the presence of suppressors of cytokine signaling (SOCS), receptors of the Tyro-3 family, adenosine and adenosine phosphates, and IL-10, is reviewed. This review presents the mechanisms involved in the control of the innate immune response by microglia in the development of neurodegenerative disorders.

Alpha-defensins block the early steps of HIV-1 infection: interference with the binding of gp120 to CD4

Alpha-defensins are antibiotic peptides that act as natural inhibitors of HIV-1 infection. However, the mechanisms of such inhibition are still unclear. Here we demonstrate that alpha-defensins block the earliest steps in the viral infectious cycle, as documented using an HIV-1 envelope-mediated cell-fusion assay. A broad-spectrum inhibitory activity was observed on primary and laboratory-adapted HIV-1 isolates irrespective of their coreceptor specificity and genetic subtype. A primary mechanism of such inhibition was identified as the ability of alpha-defensins to bind specifically both to the primary HIV-1 cellular receptor, CD4, and to the viral envelope glycoprotein, gp120. Moreover, treatment of CD4+ T cells with alpha-defensins caused a dramatic downmodulation of CD4 expression. By monoclonal antibody competition, the regions of interaction with alpha-defensins were mapped to the D1 domain of CD4 and to a surface contiguous to the CD4- and coreceptor-binding sites of gp120. Consistent with these findings, alpha-defensins inhibited the binding of gp120 to CD4. These data demonstrate that alpha-defensins specifically block the initial phase of the HIV infectious cycle and modulate the expression of CD4, a critical receptor in the physiology of T-cell activation.

Impact of microbicides and sexually transmitted infections on mucosal immunity in the female genital tract

Human immunodeficiency virus, genital herpes, and other sexually transmitted infections are a critical national and global health priority requiring the rapid development of safe and effective control methods. Topical microbicides, self-administered agents designed for vaginal use, that block transmission at the mucosal surface may provide a realistic method of intervention that could be distributed worldwide. An optimal microbicide should protect against infection but must also be safe, without adversely affecting the mucosal environment, including mediators of host defense. Thus, a critical component in microbicides development is to identify optimal assays that could serve as surrogate markers to predict safety of microbicides prior to embarking on large-scale clinical trials. This will require a greater understanding of the mediators of mucosal immunity in the female genital tract.

Breast milk alpha-defensins are associated with HIV type 1 RNA and CC chemokines in breast milk but not vertical HIV type 1 transmission

Alpha-defensins are proteins exhibiting in vitro anti-HIV-1 activity that may protect against mother-to-child transmission of HIV-1 via breast milk. Correlates of alpha-defensins in breast milk and transmission risk were determined in a cohort of HIV-1-infected pregnant women in Nairobi followed for 12 months postpartum with their infants. Maternal blood was collected antenatally and at delivery for HIV-1 viral load and infant HIV-1 infection status was determined < 48 h after birth and at months 1, 3, 6, 9, and 12. Breast milk specimens collected at month 1 were assayed for alpha-defensins, HIV-1 RNA, subclinical mastitis, and CC and CXC chemokines. We detected alpha-defensins in breast milk specimens from 108 (42%) of 260 HIV-1-infected women. Women with detectable alpha-defensins (> or =50 pg/ml) had a median concentration of 320 pg/ml and significantly higher mean breast milk HIV-1 RNA levels than women with undetectable alpha-defensins (2.9 log(10) copies/ml versus 2.5 log(10) copies/ml, p = 0.003). Increased alpha-defensins concentrations in breast milk were also associated with subclinical mastitis (Na (+)/K(+) ratio > 1) and increased breast milk chemokine levels. Overall, 40 (15%) infants were HIV-1 uninfected at birth and subsequently acquired HIV-1. There was no significant association between month 1 alpha-defensins and risk of HIV-1 transmission. In conclusion, alpha-defensins were associated with breast milk HIV-1 viral load, chemokine levels, and subclinical mastitis, all of which may alter risk of infant HIV-1 acquisition. Despite these associations there was no significant relationship between breast milk alpha-defensins and mother-to-child transmission, suggesting a complex interplay between breast milk HIV-1, inflammation, and antiinfective factors.

Human α- and β-Defensins Block Multiple Steps in Herpes Simplex Virus Infection

This study examined the ability of nine human defensins (HD) to protect against herpes simplex virus infection. Noncytotoxic concentrations of all six alpha-defensins (HNP1-4, HD5, and HD6) and human beta-defensin (hBD) 3 inhibited HSV infection. Two other beta-defensins, hBD1 and 2, lacked this protective activity. Synchronized assays revealed that HNP-4, HD6, and hBD3 acted primarily by preventing binding and entry, whereas HNP1-3 and HD5 also inhibited postentry events. Even when added several hours after entry, substantial reduction in viral gene expression ensued. Human cervical epithelial cells incubated with HNP-1 or HD5 accumulated the peptides intracellularly. Surface plasmon resonance studies revealed that HNPs 1, 2, 3, and HD5 bound HSV glycoprotein B (gB) with high affinity, but showed minimal binding to heparan sulfate, the receptor for attachment. In contrast, HNP-4 and HD6 bound heparan sulfate, but not gB. HBD3 bound both gB and heparan sulfate, but hBD1 and hBD2 bound neither. Admixture of HD5 with hydroxyethylcellulose significantly protected mice from a viral challenge lethal to controls receiving an inactive peptide or hydroxyethylcellulose alone. These findings demonstrate that HDs act at multiple steps in the HSV life cycle and support the development of defensins or defensin-like peptides as microbicides.

The role of defensins in virus-induced asthma

Respiratory viruses appear to play a central role in asthma pathogenesis. In addition to a major role in triggering asthma exacerbations, viral infections early in life may play a role in disease development. Although defensins were initially identified as antimicrobial peptides, recent studies have demonstrated that they have a much broader range of actions that are of relevance to virally induced asthma. Defensins are not only induced during viral infections, they exert direct antiviral actions against some enveloped viruses, and also can impair viral infection of cells. In addition, defensins modulate the activity of several cell types that contribute to innate immunity, including mast cells, epithelial cells, natural killer cells, and dendritic cells. They also have the capacity to modulate adaptive immunity and to contribute to airway remodeling. In this article, recent advances in these areas are reviewed in the context of the potential role of defensins in virus-induced asthma.

Innate defense against influenza A virus: activity of human neutrophil defensins and interactions of defensins with surfactant protein D

Surfactant protein D (SP-D) plays important roles in innate host defense against influenza A virus (IAV) infection, in part by modifying interactions with neutrophils. Human neutrophil defensins (HNPs) inhibit infectivity of enveloped viruses, including IAV. Our goal in this study was to characterize antiviral interactions between SP-D and HNPs. Recombinant and/or natural forms of SP-D and related collectins and HNPs were tested for antiviral activity against two different strains of IAV. HNPs 1 and 2 did not inhibit viral hemagglutination activity, but they interfered with the hemagglutination-inhibiting activity of SP-D. HNPs had significant viral neutralizing activity against divergent IAV strains. However, the HNPs generally had competitive effects when combined with SP-D in assays using an SP-D-sensitive IAV strain. In contrast, cooperative antiviral effects were noted in some instances when relatively SP-D-resistant strains were treated with SP-D and HNPs. HNPs were found to bind to the neck and/or carbohydrate recognition domain of SP-D. This binding was specific because no, or minimal, binding to other collectins was found. HNPs precipitated SP-D from bronchoalveolar lavage fluid and reduced the antiviral activity of bronchoalveolar lavage fluid. HNP-1 and -2 differed somewhat in their independent antiviral activity and their binding to SP-D. These results are relevant to the early phase of host defense against IAV, and suggest a complex interplay between SP-D and HNPs at sites of active inflammation.

Human alpha-defensins block papillomavirus infection

Sexually transmitted human papillomaviruses (HPVs) are the primary cause of cervical cancer. Recent advances in techniques for production of papillomaviral vectors [known as pseudoviruses (PsVs)] have made it possible to perform high-throughput screens for compounds that might block the initial stages of papillomavirus infection. We have used PsVs to screen a variety of compounds that might function as inhibitors of HPV infection, with emphasis on human peptides previously implicated in innate antimicrobial immunity. Little is known about the possible activity of these peptides against nonenveloped viruses, such as HPVs. Our screen revealed that human alpha-defensins 1-3 [known as human neutrophil peptides (HNPs) 1-3] and human alpha-defensin 5 (HD-5) are potent antagonists of infection by both cutaneous and mucosal papillomavirus types. In contrast, human beta-defensins 1 and 2 displayed little or no anti-HPV activity. HD-5 was particularly active against sexually transmitted HPV types, with 50% inhibitory doses in the high ng/ml range. Microscopic studies of PsV inhibition by the alpha-defensins revealed that they block virion escape from endocytic vesicles but not virion binding or internalization. Consistent with this finding, PsVs remained susceptible to inhibition by alpha-defensins for many hours after initial binding to cells. HNPs 1-3 and HD-5 have been reported to be present in the female genital tract at levels that overlap those that inhibit HPVs in vitro, suggesting that they could present a natural barrier to the sexual transmission of HPV and could serve as the basis of a broad-spectrum topical microbicide.

Cationic polypeptides are required for anti-HIV-1 activity of human vaginal fluid

Mucosal surfaces of the vagina are the portals for heterosexual transmission of HIV-1 and therefore play a fundamental role in the pathogenesis of primary infection. In the search for direct biological evidence for the role of human vaginal fluid in innate host defense, we characterized the anti-HIV-1 function of cationic polypeptides within minimally manipulated vaginal fluid. In the current study we revealed that vaginal fluid confers intrinsic anti-HIV-1 properties against both X4 and R5 strains of HIV-1 and could protect against HIV-1 infection and reduce proviral genome integration in organotypic cultures of human cervicovaginal tissue. The majority of this activity was contained in the cationic polypeptide fraction, and the depletion of cationic polypeptides using a selective cation exchange resin ablated most of the intrinsic activity against HIV-1. By adding the cationic polypeptide fraction to depleted vaginal fluid, we were able to restore activity against HIV-1. Using a proteomic approach, we identified 18 cationic polypeptides within vaginal fluid, nearly all of which are either known antimicrobials or have other purported roles in host defense. Interestingly, physiologic concentrations of 13 of the cationic polypeptides were not active alone against HIV-1, yet in concert they partially restored the anti-HIV-1 activity of cation-depleted vaginal fluid. These results suggest that synergism between cationic polypeptides is complex, and full anti-HIV-1 activity probably involves the aggregate of the cationic peptides and proteins in vaginal fluid.