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 is 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.

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Organoids mirror in vivo tissue organization and are powerful tools to investigate the development and cell biology of the small intestine. However, their application for the study of host-pathogen interactions has been largely unexplored. We have established a model using microinjection of organoids to mimic enteric infection, allowing for direct examination of pathogen interactions with primary epithelial cells in the absence of confounding variables introduced by immune cells or the commensal microbiota. We investigated the impact of Paneth cell α-defensin antimicrobial peptides on bacterial growth. We demonstrate that organoids form a sealed lumen which contains concentrations of α-defensins capable of restricting growth of multiple strains of Salmonella enterica serovar Typhimurium for at least 20 h post-infection. Transgenic expression of human defensin 5 (HD5) in mouse organoids lacking functional murine α-defensins partially restored bacterial killing. We also found that organoids from NOD2−/− mice were not impaired in α-defensin expression or antibacterial activity. This model is optimized for the study of non-invasive bacteria, but can be extended to other enteric pathogens and is amenable to further genetic manipulation of both the host and microbe to dissect this critical interface of host defense.

Background:The molecular basis for human ␣-defensin 5 (HD5) binding to non-enveloped viruses is unknown. Results: Residues critical for virus binding and antiviral activity were identified by mutational analysis. Conclusion: Multimerization, hydrophobicity, and specific arginine residues dictate HD5 antiviral activity. Significance: These studies inform the role of enteric ␣-defensins in immunity against non-enveloped viruses.

Background The lack of biomarkers that are predictive of safety is a critical gap in the development of microbicides. The present experiments were designed to evaluate the predictive value of in vitro models of microbicide safety. Methods Changes in the epithelial barrier were evaluated by measuring transepithelial electrical resistance (TER) after exposure of human epithelial cells to candidate microbicides in a dual-chamber system. The significance of observed changes was addressed by challenging cultures with human immuodeficiency virus (HIV) and measuring the ability of virus to cross the epithelium and infect target T cells cultured in the lower chamber. Results Exposure to nonoxynol-9 (N-9) or cellulose sulfate (CS), but not 9-[2-(phosphonomethoxy)propyl]adenine (also referred to as tenofovir) or PRO2000, resulted in a rapid and sustained reduction in TER and a marked increase in HIV infection of T cells cultured in the lower chamber. Moreover, CS triggered nuclear factor κB activation in peripheral blood mononuclear cells and increased HIV replication in chronically infected U1 cells. Conclusions Epithelial barrier disruption and enhanced viral replication may have contributed to the increased risk of HIV acquisition observed in phase 3 trials of N-9 and CS. Expansion of in vitro safety testing to include these models would provide a more stringent preclinical assessment of microbicide safety and may prove to be more predictive of clinical outcomes.

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The development of novel strategies to eradicate herpes simplex virus (HSV) is a global public health priority. While acyclovir and related nucleoside analogues provide successful modalities for treatment and suppression, HSV remains highly prevalent worldwide and is a major cofactor fueling the HIV epidemic. HSV is the predominant cause of genital ulcerative disease, and neonatal and sporadic infectious encephalitis. Asymptomatic shedding, which occurs more frequently than previously appreciated, contributes to viral transmission. Acyclovir resistance may be problematic for immunocompromised patients and highlights the need for new safe and effective agents. Ideally, vaccines to prevent infection, drugs to inhibit the establishment of or reactivation from latency, or vaginal microbicides to prevent sexual and perinatal transmission are needed to control the epidemic. This review summarizes current therapeutic options and strategies in development. Keywords acyclovir; herpes simplex virus; microbicide; vaccineThe discovery of acyclovir (ACV), a nucleoside analogue that is selectively phosphorylated by herpes simplex virus (HSV) and inhibits viral replication by acting as a substrate for viral DNA polymerase, ushered in a new era in antiviral chemo therapy [1,2]. Despite the overwhelming success of ACV and related drugs, HSV remains a major global health problem, and is the leading cause of encephalitis and genital ulcerative disease, and a major cofactor for HIV infection. This reflects, in part, the ability of the virus to uniformly establish latency, reactivate frequently and to be horizontally and vertically transmitted during periods of