Diagnosis of Post-Hematopoietic Stem Cell Transplantation Bronchiolitis Obliterans Syndrome in Children: Time for a Rethink?

Hematopoietic stem cell transplantation (HSCT) is undertaken in children with the aim of curing a range of malignant and nonmalignant conditions. Unfortunately, pulmonary complications, especially bronchiolitis obliterans syndrome (BOS), are significant sources of morbidity and mortality post-HSCT. Currently, criteria developed by a National Institutes of Health (NIH) working group are used to diagnose BOS in children post-HSCT. Unfortunately, during the development of a recent American Thoracic Society (ATS) Clinical Practice Guideline on this topic, it became apparent that the NIH criteria have significant limitations in the pediatric population, leading to late diagnosis of BOS. Specific limitations include use of an outdated pulmonary function testing reference equation, a reliance on spirometry, use of a fixed forced expiratory volume in 1 second (FEV1) threshold, focus on obstructive defects defined by FEV1/vital capacity, and failure to acknowledge that BOS and infection can coexist. In this review, we summarize the evidence regarding the limitations of the current criteria. We also suggest potential evidence-based ideas for improving these criteria. Finally, we highlight a new proposed criteria for post-HSCT BOS in children that were developed by the authors of the recently published ATS clinical practice guideline, along with a pathway forward for improving timely diagnosis of BOS in children post-HSCT.

Detection of Bronchiolitis Obliterans Syndrome Following Pediatric Hematopoietic Stem Cell Transplantation. An Official American Thoracic Society Clinical Practice Guideline.

BACKGROUND: Many children undergo allogeneic Hematopoietic Stem Cell Transplantation (HSCT) for the treatment of malignant and non-malignant conditions. Unfortunately, pulmonary complications occur frequently post-HSCT, with bronchiolitis obliterans syndrome (BOS) being the most common non-infectious pulmonary complication. Current international guidelines contain conflicting recommendations regarding post-HSCT surveillance for BOS, and a recent National Institutes of Health workshop highlighted the need for a standardized approach to post-HSCT monitoring. As such, this guideline provides an evidence-based approach to detection of post-HSCT BOS in children. METHODS: A multinational, multidisciplinary panel of experts identified six questions regarding surveillance for, and evaluation of post-HSCT BOS in children. Systematic review of the literature was undertaken to answer each question. The Grading of Recommendations, Assessment, Development, and Evaluation approach was used to rate the quality of evidence and the strength of recommendations. RESULTS: The panel members considered the strength of each recommendation and evaluated the benefits and risks of applying the intervention. In formulating the recommendations, the panel considered patient and caregiver values, the cost of care, and feasibility. Recommendations addressing the role of screening pulmonary function testing and diagnostic tests in children with suspected post-HSCT BOS were made. Following a Delphi process, new diagnostic criteria for pediatric post-HSCT BOS were also proposed. CONCLUSIONS: This document provides an evidence-based approach to detection of post-HSCT BOS in children, while also highlighting considerations for implementation of each recommendation. Further, the document describes important areas for future research.

Multiple steps of prion strain adaptation to a new host.

The transmission of prions across species is a critical aspect of their dissemination among mammalian hosts, including humans. This process often necessitates strain adaptation. In this study, we sought to investigate the mechanisms underlying prion adaptation while mitigating biases associated with the history of cross-species transmission of natural prion strains. To achieve this, we utilized the synthetic hamster prion strain S05. Propagation of S05 using mouse PrPC in Protein Misfolding Cyclic Amplification did not immediately overcome the species barrier. This finding underscores the involvement of factors beyond disparities in primary protein structures. Subsequently, we performed five serial passages to stabilize the incubation time to disease in mice. The levels of PrPSc increased with each passage, reaching a maximum at the third passage, and declining thereafter. This suggests that only the initial stage of adaptation is primarily driven by an acceleration in PrPSc replication. During the protracted adaptation to a new host, we observed significant alterations in the glycoform ratio and sialylation status of PrPSc N-glycans. These changes support the notion that qualitative modifications in PrPSc contribute to a more rapid disease progression. Furthermore, consistent with the decline in sialylation, a cue for "eat me" signaling, the newly adapted strain exhibited preferential colocalization with microglia. In contrast to PrPSc dynamics, the intensity of microglia activation continued to increase after the third passage in the new host. In summary, our study elucidates that the adaptation of a prion strain to a new host is a multi-step process driven by several factors.

Infant periodic breathing and apneic threshold.

A mathematical model was proposed to predict the role played by apneic threshold in periodic breathing in preterm infants. Prior models have mainly applied linear control theory which predicted instability but could not explain sustained periodic breathing. Apneic threshold to CO2 which has been postulated to play a major role in infant periodic breathing is a nonlinear effect and cannot be described by linear theory. Another previously unexplored nonlinear factor affecting instability is brain vascular volume change with CO2 which affects time delay to chemoreceptors. The current model explored the influences of apneic threshold, central and peripheral chemoreceptor gains, cardiac output, lung volume, and circulatory time delay on periodic breathing. Apneic threshold was found to play a major role in ventilatory responses to spontaneous sighs. Sighs led to apneic pauses followed by periods of periodic breathing with peripheral chemoreceptor CO2 gain, cardiac output, and lung volume were at reported normal levels. Apneic threshold when exceeded was observed to cause an asymmetry in the periodic breathing cycling and an increased periodic breathing frequency. Sighs in infants occur frequently enough to lead to repeated stimulation within the epoch duration of periodic breathing for a single sigh. Multiple sighs may then play a major role in promoting continuous periodic breathing in infants. Peripheral chemoreceptor gain estimated using endogenous CO2 led to validated predicted periodic breathing cycle duration as a function of age. Brain vascular volume increase with CO2 contributes to periodic breathing in very young (1-2 day old) preterm infants.

Determining an Optimal Oxygen Saturation Target Range Based on Neonatal Maturity: Demonstration of a Decision Tree Analytic.

The utility of decision tree machine learning in exploring the interactions among the SpO2 target range, neonatal maturity, and oxemic-risk is demonstrated. METHODS: This observational study used 3 years of paired age-SpO2-PaO2 data from a neonatal ICU. The CHAID decision tree method was used to explore the interaction of postmenstrual age (PMA) on the risk of extreme arterial oxygen levels at six different potential SpO2 target ranges (88-92%, 89-93%, 90-94%, 91-95%, 92-96% and 93-97%). Risk was calculated using a severity-weighted average of arterial oxygen outside the normal range for neonates (50-80 mmHg). RESULTS: In total, 7500 paired data points within the potential target range envelope were analyzed. The two lowest target ranges were associated with the highest risk, and the ranges of 91-95% and 92-96% were associated with the lowest risk. There were shifts in the risk associated with PMA. All the target ranges showed the lowest risk at ≥42 weeks PMA. The lowest risk for preterm infants was within a target range of 92-96% with a PMA of ≤34 weeks. CONCLUSIONS: This study demonstrates the utility of decision tree analytics. These results suggest that SpO2 target ranges that are different from typical range might reduce morbidity and mortality. Further research, including prospective randomized trials, is warranted.

Multiple steps of prion strain adaptation to a new host.

The transmission of prions across species is a critical aspect of their dissemination among mammalian hosts, including humans. This process often necessitates strain adaptation. In this study, we sought to investigate the mechanisms underlying prion adaptation while mitigating biases associated with the history of cross-species transmission of natural prion strains. To achieve this, we utilized the synthetic hamster prion strain S05. Propagation of S05 using mouse PrPC in Protein Misfolding Cyclic Amplification did not immediately overcome the species barrier. This finding underscores the involvement of factors beyond disparities in primary protein structures. Subsequently, we performed five serial passages to stabilize the incubation time to disease in mice. The levels of PrPSc increased with each passage, reaching a maximum at the third passage, and declining thereafter. This suggests that only the initial stage of adaptation is primarily driven by an acceleration in PrPSc replication. During the protracted adaptation to a new host, we observed significant alterations in the glycoform ratio and sialylation status of PrPSc N-glycans. These changes support the notion that qualitative modifications in PrPSc contribute to a more rapid disease progression. Furthermore, consistent with the decline in sialylation, a cue for "eat me" signaling, the newly adapted strain exhibited preferential colocalization with microglia. In contrast to PrPSc dynamics, the intensity of microglia activation continued to increase after the third passage in the new host. In summary, our study elucidates that the adaptation of a prion strain to a new host is a multi-step process driven by several factors.

Molecular basis of the pleiotropic effects by the antibiotic amikacin on the ribosome.

Aminoglycosides are a class of antibiotics that bind to ribosomal RNA and exert pleiotropic effects on ribosome function. Amikacin, the semisynthetic derivative of kanamycin, is commonly used for treating severe infections with multidrug-resistant, aerobic Gram-negative bacteria. Amikacin carries the 4-amino-2-hydroxy butyrate (AHB) moiety at the N1 amino group of the central 2-deoxystreptamine (2-DOS) ring, which may confer amikacin a unique ribosome inhibition profile. Here we use in vitro fast kinetics combined with X-ray crystallography and cryo-EM to dissect the mechanisms of ribosome inhibition by amikacin and the parent compound, kanamycin. Amikacin interferes with tRNA translocation, release factor-mediated peptidyl-tRNA hydrolysis, and ribosome recycling, traits attributed to the additional interactions amikacin makes with the decoding center. The binding site in the large ribosomal subunit proximal to the 3'-end of tRNA in the peptidyl (P) site lays the groundwork for rational design of amikacin derivatives with improved antibacterial properties.

Reactive astrocytes associated with prion disease impair the blood brain barrier.

BACKGROUND: Impairment of the blood-brain barrier (BBB) is considered to be a common feature among neurodegenerative diseases, including Alzheimer's, Parkinson's and prion diseases. In prion disease, increased BBB permeability was reported 40 years ago, yet the mechanisms behind the loss of BBB integrity have never been explored. Recently, we showed that reactive astrocytes associated with prion diseases are neurotoxic. The current work examines the potential link between astrocyte reactivity and BBB breakdown. RESULTS: In prion-infected mice, the loss of BBB integrity and aberrant localization of aquaporin 4 (AQP4), a sign of retraction of astrocytic endfeet from blood vessels, were noticeable prior to disease onset. Gaps in cell-to-cell junctions along blood vessels, together with downregulation of Occludin, Claudin-5 and VE-cadherin, which constitute tight and adherens junctions, suggested that loss of BBB integrity is linked with degeneration of vascular endothelial cells. In contrast to cells isolated from non-infected adult mice, endothelial cells originating from prion-infected mice displayed disease-associated changes, including lower levels of Occludin, Claudin-5 and VE-cadherin expression, impaired tight and adherens junctions, and reduced trans-endothelial electrical resistance (TEER). Endothelial cells isolated from non-infected mice, when co-cultured with reactive astrocytes isolated from prion-infected animals or treated with media conditioned by the reactive astrocytes, developed the disease-associated phenotype observed in the endothelial cells from prion-infected mice. Reactive astrocytes were found to produce high levels of secreted IL-6, and treatment of endothelial monolayers originating from non-infected animals with recombinant IL-6 alone reduced their TEER. Remarkably, treatment with extracellular vesicles produced by normal astrocytes partially reversed the disease phenotype of endothelial cells isolated from prion-infected animals. CONCLUSIONS: To our knowledge, the current work is the first to illustrate early BBB breakdown in prion disease and to document that reactive astrocytes associated with prion disease are detrimental to BBB integrity. Moreover, our findings suggest that the harmful effects are linked to proinflammatory factors secreted by reactive astrocytes.

Reactive astrocytes associated with prion disease impair the blood brain barrier.

Background: Impairment of the blood-brain barrier (BBB) is considered to be a common feature among neurodegenerative diseases, including Alzheimer's, Parkinson's and prion diseases. In prion disease, increased BBB permeability was reported 40 years ago, yet the mechanisms behind the loss of BBB integrity have never been explored. Recently, we showed that reactive astrocytes associated with prion diseases are neurotoxic. The current work examines the potential link between astrocyte reactivity and BBB breakdown. Results: In prion-infected mice, the loss of BBB integrity and aberrant localization of aquaporin 4 (AQP4), a sign of retraction of astrocytic endfeet from blood vessels, were noticeable prior to disease onset. Gaps in cell-to-cell junctions along blood vessels, together with downregulation of Occludin, Claudin-5 and VE-cadherin, which constitute tight and adherens junctions, suggested that loss of BBB integrity is linked with degeneration of vascular endothelial cells. In contrast to cells isolated from non-infected adult mice, endothelial cells originating from prion-infected mice displayed disease-associated changes, including lower levels of Occludin, Claudin-5 and VE-cadherin expression, impaired tight and adherens junctions, and reduced trans-endothelial electrical resistance (TEER). Endothelial cells isolated from non-infected mice, when co-cultured with reactive astrocytes isolated from prion-infected animals or treated with media conditioned by the reactive astrocytes, developed the disease-associated phenotype observed in the endothelial cells from prion-infected mice. Reactive astrocytes were found to produce high levels of secreted IL-6, and treatment of endothelial monolayers originating from non-infected animals with recombinant IL-6 alone reduced their TEER. Remarkably, treatment with extracellular vesicles produced by normal astrocytes partially reversed the disease phenotype of endothelial cells isolated from prion-infected animals. Conclusions: To our knowledge, the current work is the first to illustrate early BBB breakdown in prion disease and to document that reactive astrocytes associated with prion disease are detrimental to BBB integrity. Moreover, our findings suggest that the harmful effects are linked to proinflammatory factors secreted by reactive astrocytes.

Invasive Ventilatory Support in Patients With Pediatric Acute Respiratory Distress Syndrome: From the Second Pediatric Acute Lung Injury Consensus Conference.

OBJECTIVE: To provide evidence for the Second Pediatric Acute Lung Injury Consensus Conference updated recommendations and consensus statements for clinical practice and future research on invasive mechanical ventilation support of patients with pediatric acute respiratory distress syndrome (PARDS). DATA SOURCES: MEDLINE (Ovid), Embase (Elsevier), and CINAHL Complete (EBSCOhost). STUDY SELECTION: We included clinical studies of critically ill patients undergoing invasive mechanical ventilation for PARDS, January 2013 to April 2022. In addition, meta-analyses and systematic reviews focused on the adult acute respiratory distress syndrome population were included to explore new relevant concepts (e.g., mechanical power, driving pressure, etc.) still underrepresented in the contemporary pediatric literature. DATA EXTRACTION: Title/abstract review, full text review, and data extraction using a standardized data collection form. DATA SYNTHESIS: The Grading of Recommendations Assessment, Development and Evaluation approach was used to identify and summarize relevant evidence and develop recommendations, good practice statements and research statements. We identified 26 pediatric studies for inclusion and 36 meta-analyses or systematic reviews in adults. We generated 12 recommendations, two research statements, and five good practice statements related to modes of ventilation, tidal volume, ventilation pressures, lung-protective ventilation bundles, driving pressure, mechanical power, recruitment maneuvers, prone positioning, and high-frequency ventilation. Only one recommendation, related to use of positive end-expiratory pressure, is classified as strong, with moderate certainty of evidence. CONCLUSIONS: Limited pediatric data exist to make definitive recommendations for the management of invasive mechanical ventilation for patients with PARDS. Ongoing research is needed to better understand how to guide best practices and improve outcomes for patients with PARDS requiring invasive mechanical ventilation.

A 5'-Flanking C/G Pair at the Core Region Enhances the Recognition and Binding of Kaiso to Methylated DNA.

Methyl CpG binding proteins (MBPs) are transcription factors that recognize the methylated CpG sites in DNA and mediate the DNA methylation signal into various downstream cellular processes. The C2H2 zinc finger (ZF) protein, Kaiso, also an MBP, preferentially binds to two symmetrically methylated CpG sites in DNA sequences via C-terminal C2H2 ZF domains and mediates the transcription regulation process. Investigation of the molecular mechanism of the recognition of methylated DNA (meDNA) by Kaiso is important to understand how this protein reads and translates this methylation signal into downstream transcription outcomes. Despite previous studies in Kaiso-meDNA interactions, detailed structural investigations on the sequence-specific interaction of Kaiso with the meDNA sequence are still lacking. In this work, we used molecular modeling and molecular dynamics (MD) simulation-based computational approaches to investigate the recognition of various methylated DNA sequences by Kaiso. Our MD simulation results show that the Kaiso-meDNA interaction is sequence specific. The recognition of meDNA by Kaiso is enhanced in the MeECad sequence compared to the MeCG2 sequence. Compared to the 5'-flanking T/A pair in MeCG2, both MeCG2_mutCG and MeECad sequences show that a C/G base pair allows GLU535 of Kaiso to preferably recognize and bind the core mCpG site. The core mCGmCG site is crucial for the recognition process and formation of a stable complex. Our results reveal that the 5'-flanking nucleotides are also important for the enhanced binding and recognition of methylated sites.

Aß plaques do not protect against HSV-1 infection in a mouse model of familial Alzheimer's disease, and HSV-1 does not induce Aß pathology in a model of late onset Alzheimer's disease.

The possibility that the etiology of late onset Alzheimer's disease is linked to viral infections of the CNS has been actively debated in recent years. According to the antiviral protection hypothesis, viral pathogens trigger aggregation of Aß peptides that are produced as a defense mechanism in response to infection to entrap and neutralize pathogens. To test the causative relationship between viral infection and Aß aggregation, the current study examined whether Aß plaques protect the mouse brain against Herpes Simplex Virus 1 (HSV-1) infection introduced via a physiological route and whether HSV-1 infection triggers formation of Aß plaques in a mouse model of late-onset AD that does not develop Aß pathology spontaneously. In aged 5XFAD mice infected via eye scarification, high density of Aß aggregates did not improve survival time or rate when compared with wild type controls. In 5XFADs, viral replication sites were found in brain areas with a high density of extracellular Aß deposits, however, no association between HSV-1 and Aß aggregates could be found. To test whether HSV-1 triggers Aß aggregation in a mouse model that lacks spontaneous Aß pathology, 13-month-old hAß/APOE4/Trem2*R47H mice were infected with HSV-1 via eye scarification with the McKrae HSV-1 strain, intracranial inoculation with McKrae, intracranial inoculation after priming with LPS for 6 weeks, or intracranial inoculation with high doses of McKrae or 17syn + strains that represent different degrees of neurovirulence. No signs of Aß aggregation were found in any of the experimental groups. Instead, extensive infiltration of peripheral leukocytes was observed during the acute stage of HSV-1 infection, and phagocytic activity of myeloid cells was identified as the primary defense mechanism against HSV-1. The current results argue against a direct causative relationship between HSV-1 infection and Aß pathology.

A Network Meta-analysis of Dexamethasone for Preventing Postextubation Upper Airway Obstruction in Children.

Rationale: Periextubation corticosteroids are commonly used in children to prevent upper airway obstruction (UAO). However, the best timing and dose combination of corticosteroids is unknown. Objectives: To compare effectiveness of different corticosteroid regimens in preventing UAO and reintubation. Methods: MEDLINE, CINAHL, and Embase search identified randomized trials in children using corticosteroids to prevent UAO. All studies used dexamethasone. The studies were categorized based on timing of initiation of dexamethasone (early use: >12 h before extubation) and the dose (high dose: ⩾0.5 mg/kg/dose). We performed Bayesian network meta-analysis with studies grouped into four regimens: high dose, early use (HE); low dose, early use (LE); high dose, late use (HL); and low dose, late use. Results: Eight trials (n = 903) were included in the analysis. For preventing UAO (odds ratio; 95% credible interval), HE (0.13; 0.04-0.36), HL (0.39; 0.19-0.74), and LE (0.15; 0.04-0.58) regimens appear to be more effective than no dexamethasone (low certainty). HE and LE had the highest probability of being the top-ranked regimens for preventing UAO (surface under the cumulative ranking curve 0.901 and 0.808, respectively). For preventing reintubation, the effect estimate was imprecise for all four dexamethasone regimens compared with no dexamethasone (very low certainty). HE and LE were the top-ranked regimens (surface under the cumulative ranking curve 0.803 and 0.720, respectively) for preventing reintubation. Sensitivity analysis showed that regimens that started >12 hours before extubation were likely more effective than regimens started >6 hours before extubation. Conclusions: Periextubation dexamethasone can prevent postextubation UAO in children, but effectiveness is highly dependent on timing and dosing regimen. Early initiation (ideally >12 h before extubation) appears to be more important than the dose of dexamethasone. Ultimately, the specific steroid strategy should be personalized, considering the potential for adverse events associated with dexamethasone and the individual risk of UAO and reintubation.

Sequence Analysis of Novel Staphylococcus aureus Lineages from Wild and Captive Macaques.

Staphylococcus aureus is a widespread and common opportunistic bacterium that can colonise or infect humans as well as a wide range of animals. There are a few studies of both methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) isolated from monkeys, apes, and lemurs, indicating a presence of a number of poorly or unknown lineages of the pathogen. In order to obtain insight into staphylococcal diversity, we sequenced strains from wild and captive individuals of three macaque species (Macaca mulatta, M. assamensis, and M. sylvanus) using Nanopore and Illumina technologies. These strains were previously identified by microarray as poorly or unknown strains. Isolates of novel lineages ST4168, ST7687, ST7688, ST7689, ST7690, ST7691, ST7692, ST7693, ST7694, ST7695, ST7745, ST7746, ST7747, ST7748, ST7749, ST7750, ST7751, ST7752, ST7753, and ST7754 were sequenced and characterised for the first time. In addition, isolates belonging to ST2990, a lineage also observed in humans, and ST3268, a MRSA strain already known from macaques, were also included into the study. Mobile genetic elements, genomic islands, and carriage of prophages were analysed. There was no evidence for novel host-specific virulence factors. However, a conspicuously high rate of carriage of a pathogenicity island harbouring edinB and etD2/etE as well as a higher number of repeat units within the gene sasG (encoding an adhesion factor) than in human isolates were observed. None of the strains harboured the genes encoding Panton-Valentine leukocidin. In conclusion, wildlife including macaques may harbour an unappreciated diversity of S. aureus lineages that may be of clinical relevance for humans, livestock, or for wildlife conservation, given the declining state of many wildlife populations.

The American Thoracic Society Guideline Methodology Training Program.

A new era in guideline creation began in 2011 with publication of the Institute of Medicine (now the National Academy of Medicine) Standards for Developing Trustworthy Clinical Practice Guidelines. The American Thoracic Society (ATS) was committed to developing guidelines in accordance with the new standards and decided that an experienced guideline methodologist would be required on ATS guideline projects to ensure correct implementation of the standards. The ATS Guideline Methodology Training Program was launched to increase the pool of trained methodologists. Each year, accepted trainees (methodology scholars) attend a workshop that introduces them to the terminology and process of guideline development and are given the option of participating in a guideline project. Scholars work with the mentorship of a lead methodologist to conduct and then present a systematic review to the guideline committee, discuss the evidence, and participate in the development of evidence-based graded recommendations. Scholars have participated in 22 ATS guidelines over the past 9 years, and most remain engaged in guideline development. For the past 2 years, the methodological aspects of all ATS guideline projects were led by graduates of the training program, and several scholars have accepted positions to lead guidelines for other professional societies. Guideline methodology is particularly suitable for clinician educators because the work is clinically oriented, and guidelines confer high academic capital. Those who elect not to continue in guideline development still acquire the skills to perform and publish systematic reviews, as well as to educate trainees in reading and reviewing literature.

Structural insights into the repair mechanism of AGT for methyl-induced DNA damage.

Methylation induced DNA base-pairing damage is one of the major causes of cancer. O6-alkylguanine-DNA alkyltransferase (AGT) is considered a demethylation agent of the methylated DNA. Structural investigations with thermodynamic properties of the AGT-DNA complex are still lacking. In this report, we modeled two catalytic states of AGT-DNA interactions and an AGT-DNA covalent complex and explored structural features using molecular dynamics (MD) simulations. We utilized the umbrella sampling method to investigate the changes in the free energy of the interactions in two different AGT-DNA catalytic states, one with methylated GUA in DNA and the other with methylated CYS145 in AGT. These non-covalent complexes represent the pre- and post-repair complexes. Therefore, our study encompasses the process of recognition, complex formation, and separation of the AGT and the damaged (methylated) DNA base. We believe that the use of parameters for the amino acid and nucleotide modifications and for the protein-DNA covalent bond will allow investigations of the DNA repair mechanism as well as the exploration of cancer therapeutics targeting the AGT-DNA complexes at various functional states as well as explorations via stabilization of the complex.

Alzheimer's disease-associated ß-amyloid does not protect against herpes simplex virus 1 infection in the mouse brain.

Alzheimer's disease (AD) is a devastating fatal neurodegenerative disease. An alternative to the amyloid cascade hypothesis is that a viral infection is key to the etiology of late-onset AD, with ß-amyloid (Aß) peptides playing a protective role. In the current study, young 5XFAD mice that overexpress mutant human amyloid precursor protein with the Swedish, Florida, and London familial AD mutations were infected with one of two strains of herpes simplex virus 1 (HSV-1), 17syn+ and McKrae, at three different doses. Contrary to previous work, 5XFAD genotype failed to protect mice against HSV-1 infection. The region- and cell-specific tropisms of HSV-1 were not affected by the 5XFAD genotype, indicating that host-pathogen interactions were not altered. Seven- to ten-month-old 5XFAD animals in which extracellular Aß aggregates were abundant showed slightly better survival rate relative to their wild-type (WT) littermates, although the difference was not statistically significant. In these 5XFAD mice, HSV-1 replication centers were partially excluded from the brain areas with high densities of Aß aggregates. Aß aggregates were free of HSV-1 viral particles, and the limited viral invasion to areas with a high density of Aß aggregates was attributed to phagocytic activity of reactive microglia. In the oldest mice (12-15 months old), the survival rate did not differ between 5XFAD and WT littermates. While the current study questions the antiviral role of Aß, it neither supports nor refutes the viral etiology hypothesis of late-onset AD.