Tau protein has long been associated with neurodegenerative diseases such as Alzheimer’s, where its hyperphosphorylated forms aggregate into neurofibrillary tangles that disrupt neuronal function. However, the study spearheaded by Eimer, Rodriguez, DeFao, and colleagues reveals an entirely different facet of phosphorylated tau, demonstrating that it can exhibit potent antimicrobial activity within human neurons. Unlike previous notions that exclusively framed phosphorylated tau as detrimental, this work illuminates its protective capabilities against viral pathogens, particularly HSV-1, which is known to cause encephalitis and has been implicated in neurodegenerative disease progression.

The research team employed advanced virological and biochemical techniques to explore interactions between phosphorylated tau and HSV-1. Their experiments revealed that phosphorylated tau directly targets viral particles, leading to their neutralization and preventing viral infection in cultured human neurons. This antiviral activity suggests that phosphorylated tau might serve as an intrinsic component of the neuronal innate immune system, bolstering defenses against neurotropic viruses.

Mechanistically, the study suggests that phosphorylation triggers conformational changes in tau, enhancing its affinity for viral components. This interaction disrupts the viral integrity or entry processes essential for productive infection. The precise biochemical pathways remain to be fully elucidated, but the data hint at a sophisticated interplay where post-translational modifications of tau convert it from a structural microtubule-associated protein into an active antiviral effector.

The implications of these findings are manifold. In the context of HSV-1, which frequently establishes latent infections within the nervous system, the presence of phosphorylated tau as an antiviral agent may represent a crucial barrier to viral reactivation and spread. This could partially explain why despite widespread HSV-1 prevalence, severe neurological outcomes remain relatively uncommon in the general population. Furthermore, it redefines phosphorylated tau’s role not merely as a pathological marker but as a dynamic participant in neuroimmune surveillance.

Beyond HSV-1, this discovery opens avenues to investigate whether tau phosphorylation can defend against other neuroinvasive pathogens, broadening our understanding of neuronal protection mechanisms. Given the increasing evidence linking viral infections to the etiopathogenesis of neurodegenerative diseases, these insights could transform therapeutic strategies, emphasizing modulation of tau phosphorylation to boost antiviral immunity while mitigating aggregation-related toxicity.

The study also prompts reevaluation of therapeutic approaches aimed at reducing tau phosphorylation or clearing phosphorylated tau aggregates. While such strategies aim to alleviate tauopathy symptoms, they may inadvertently compromise the brain’s ability to counteract viral challenges. Delicate balancing of tau’s protective and pathological roles may become a critical consideration for future drug development.

Researchers underscore that the antimicrobial function of phosphorylated tau likely represents an evolutionary adaptation, reflecting the constant battle between host defenses and viral pathogens in the central nervous system. This evolutionary perspective enhances our appreciation of tau’s multifaceted biology, situating it within an immune context rather than viewing it solely through the lens of neurodegeneration.

The interplay between viral infection and tau pathology has long intrigued neuroscientists, with some hypotheses positing that viral insults may trigger or exacerbate tau hyperphosphorylation and aggregation. This study suggests a bidirectional relationship where tau phosphorylation initiates as a protective response, but chronic activation or dysregulation could culminate in pathological outcomes. Such nuanced insights advance the field’s understanding of disease mechanisms and encourage refined models integrating infection, immunity, and neurodegeneration.

Furthermore, the research leveraged cutting-edge human neuronal culture systems, allowing for precise dissection of molecular interactions in relevant cell types. This technological advancement strengthens the validity of findings and provides a robust platform for follow-up investigations that might include in vivo validation or therapeutic screening.

The discovery also invites exploration of potential biomarkers based on tau phosphorylation patterns that correlate with antiviral efficacy, potentially serving as predictive indicators of viral susceptibility or progression in neurological contexts. Such biomarkers could guide personalized medical interventions or monitoring strategies for at-risk populations.

From a broader perspective, this research prompts a reconsideration of the central nervous system’s immunological capabilities. Traditionally regarded as immunoprivileged, the brain’s intrinsic defense mechanisms continue to reveal complex layers of protection involving proteins like phosphorylated tau, expanding the paradigm of neuroimmune interactions.

In conclusion, the identification of phosphorylated tau as a participant in combating herpes simplex virus 1 infection reshapes our understanding of the protein’s function beyond neuropathology, highlighting an essential role in neuronal innate immunity. These findings not only deepen scientific comprehension of tau biology and neurovirology but also offer promising directions for therapeutic innovation targeting neurodegenerative and neuroinfectious diseases.

Subject of Research:
Phosphorylated tau protein’s antimicrobial activity, specifically its role in neutralizing herpes simplex virus 1 infectivity in human neurons.

Article Title:
Phosphorylated tau exhibits antimicrobial activity capable of neutralizing herpes simplex virus 1 infectivity in human neurons.

Article References:
Eimer, W.A., Rodriguez, A.S., DeFao, M.T. et al. Phosphorylated tau exhibits antimicrobial activity capable of neutralizing herpes simplex virus 1 infectivity in human neurons. Nat Neurosci (2025). https://doi.org/10.1038/s41593-025-02157-0

Image Credits:
AI Generated

DOI:
https://doi.org/10.1038/s41593-025-02157-0

Glycoprotein B, a key viral envelope protein, is indispensable for herpesvirus entry into host cells, mediating membrane fusion during viral infection. Its dynamic structural rearrangements, shifting between prefusion and postfusion conformations, have historically complicated efforts to design effective inhibitors. Researchers have now illuminated this challenging target by isolating a nanobody, Nb1_gbHSV, that exhibits a striking preference for the prefusion form, a conformation transiently adopted during the virus’s entry process.

High-resolution cryo-electron microscopy of gB bound by Nb1_gbHSV revealed a detailed interaction landscape. The nanobody engages simultaneously with three distinct domains on gB, namely Di, Diii, and Div. This multifunctional engagement is stabilised through an extraordinary network of 23 hydrogen bonds and eight salt bridges, resulting in an extensive buried surface area measuring approximately 1,260 Ų. Such intimate molecular interactions underscore the nanobody’s formidable binding affinity.

Residue R102 on Nb1_gbHSV plays a pivotal role, protruding into the interface between Div and Di to form additional hydrogen bonds with Di and Diii of the same protomer. This precise targeting is significant because Di and Div reside in proximity only in the prefusion conformation; in the postfusion state, these domains are widely separated. Consequently, the nanobody’s epitope is structurally accessible solely in the prefusion form, conferring a remarkable degree of conformation specificity.

Functional assays substantiated the nanobody’s selective affinity, with microscale thermophoresis revealing a dissociation constant (KD) around an extraordinarily low 14 picomolar for prefusion gB, whereas no measurable binding occurred with the postfusion form. This demonstrates the nanobody’s potential to act as a prefusion-specific antagonist, a critical advantage as viral fusion proteins often evade neutralization by transitioning to postfusion states.

Cross-reactivity assays provided further excitement, as Nb1_gbHSV was found to bind gB from both HSV-1 and HSV-2. Despite low conservation of the epitope among other human-infecting herpesviruses such as varicella-zoster virus (VZV), cytomegalovirus (HCMV), and Epstein-Barr virus (EBV), the nanobody’s binding to HSV-2 gB is likely underpinned by the high sequence similarity in this region between HSV-1 and HSV-2. This cross-species reactivity enhances the therapeutic promise of Nb1_gbHSV.

Cellular localization experiments using fluorescently labelled Nb1_gbHSV confirmed the nanobody’s ability to bind gB expressed on the plasma membrane of transfected baby hamster kidney (BHK-21) cells. Co-localization with green fluorescent protein tags on gB reinforced these findings, with evidence suggesting rapid internalization of the nanobody-gB complex via endocytosis. This internal trafficking indicates the nanobody does not interrupt native cellular machinery, a critical consideration for therapeutic applications that require minimal off-target effects.

Structural modeling further supports the prefusion-specific nature of Nb1_gbHSV. When computationally docked onto the postfusion conformation of gB, the nanobody induces steric clashes between domains, particularly Div and Di of adjacent protomers, implicating an unstable interaction. This implies that Nb1_gbHSV likely stabilizes the prefusion form, preventing the conformational changes necessary for viral membrane fusion, thus neutralizing viral infectivity.

This discovery marks a significant milestone in the development of nanobody-based therapeutics against herpesviruses. Nanobodies, due to their small size and stability, offer distinct advantages over conventional antibodies, including higher tissue penetration and ease of manufacturing. The selective targeting of a metastable prefusion state presents a compelling antiviral approach, potentially limiting viral spread and ameliorating disease severity.

Moreover, the detailed characterization of the Nb1_gbHSV binding interface opens avenues for rational drug design. Small molecules or engineered biologics mimicking this interface could be developed to enhance the antiviral arsenal against herpesviruses. Additionally, the unique epitopic site defined by the proximity of Di and Div domains provides a blueprint for future vaccines aimed at eliciting broadly neutralizing antibodies against HSV-1 and HSV-2.

The research also underscores the importance of nanobody technology in virology. By exploiting their unique binding modalities and conformational selectivity, nanobodies can illuminate viral protein dynamics and provide effective means to disrupt viral life cycles. Nb1_gbHSV exemplifies this potential, evidencing high specificity without compromising cellular functions such as endocytosis, a balance essential for safe therapeutic application.

As HSV remains a significant global health burden — with tens of millions affected worldwide, and complications ranging from painful mucocutaneous lesions to neuroinvasive diseases — the emergence of such innovative molecular tools is urgently needed. Nb1_gbHSV’s ability to differentiate viral conformations and cross-react with multiple HSV species suggests a versatile template for future antiviral therapies that could surpass current treatment limitations.

Continuing structural and functional analyses are anticipated to further clarify the mechanisms by which Nb1_gbHSV exerts viral neutralization in vivo. Future studies will also explore its therapeutic efficacy, pharmacodynamics, and potential integration into clinical regimens. The promise of neutralizing gB at its prefusion conformation heralds a new frontier for vaccines and biologics against herpes simplex viruses.

In summary, Nb1_gbHSV represents a transformative breakthrough in herpesvirus research, epitomizing the intersection of structural biology, immunology, and nanobody engineering. By harnessing prefusion specificity and cross-species reactivity, this molecule exemplifies next-generation antiviral strategies poised to mitigate the global impact of HSV infections.

Subject of Research: Nanobody-mediated neutralization of herpes simplex virus glycoprotein B prefusion conformation

Article Title: A nanobody specific to prefusion glycoprotein B neutralizes HSV-1 and HSV-2

Article References:
Vollmer, B., Ebel, H., Rees, R. et al. A nanobody specific to prefusion glycoprotein B neutralizes HSV-1 and HSV-2. Nature (2025). https://doi.org/10.1038/s41586-025-09438-5