Relationship between herpes simplex virus-1-specific antibody titers and cortical brain damage in Alzheimer's disease and amnestic mild cognitive impairment

Integrative Multi-omics Analysis to Characterize Herpes Virus Infection Increases the Risk of Alzheimer's Disease

Evidence suggests that herpes virus infection is associated with an increased risk of Alzheimer's disease (AD), and innate and adaptive immunity plays an important role in the association. Although there have been many studies, the mechanism of the association is still unclear. This study aims to reveal the underlying molecular and immune regulatory network through multi-omics data and provide support for the study of the mechanism of infection and AD in the future. Here, we found that the herpes virus infection significantly increased the risk of AD. Genes associated with the occurrence and development of AD and genetically regulated by herpes virus infection are mainly enrichment in immune-related pathways. The 22 key regulatory genes identified by machine learning are mainly immune genes. They are also significantly related to the infiltration changes of 3 immune cell in AD. Furthermore, many of these genes have previously been reported to be linked, or potentially linked, to the pathological mechanisms of both herpes virus infection and AD. In conclusion, this study contributes to the study of the mechanisms related to herpes virus infection and AD, and indicates that the regulation of innate and adaptive immunity may be an effective strategy for preventing and treating herpes virus infection and AD. Additionally, the identified key regulatory genes, whether previously studied or newly discovered, may serve as valuable targets for prevention and treatment strategies.

Specific and cumulative infection burden and mild cognitive impairment and dementia: A population-based study

Infection by pathogenic microbes is widely hypothesized to be a risk factor for the development of neurocognitive disorders and dementia, but evidence remains limited. We analyzed the association of seropositivity to 11 common pathogens and cumulative infection burden with neurocognitive disorder (mild cognitive impairment and dementia) in a population-based cohort of 475 older individuals (mean age = 67.6 y) followed up over 3-5 years for the risk of MCI-dementia. Specific seropositivities showed a preponderance of positive trends of association with MCI-dementia, including for Plasmodium, H. pylori, and RSV (p < 0.05), as well as Chickungunya, HSV-2, CMV and EBV (p > 0.05), while HSV-1 and HHV-6 showed equivocal or no associations, and Dengue and VZV showed negative associations (p < 0.05) with MCI-dementia. High infection burden (5 + cumulated infections) was significantly associated with an increased MCI-dementia risk in comparison with low infection burden (1-3 cumulative infections), adjusted for age, sex, and education. Intriguingly, for a majority (8 of 11) of pathogens, levels of antibody titers were significantly lower in those with MCI-dementia compared to cognitive normal individuals. Based on our observations, we postulate that individuals who are unable to mount strong immunological responses to infection by diverse microorganisms, and therefore more vulnerable to infection by greater numbers of different microbial pathogens or repeated infections to the same pathogen in the course of their lifetime are more likely to develop MCI or dementia. This hypothesis should be tested in more studies.

Herpes simplex virus infection and the risk of dementia: a systematic review and meta-analysis

Aim

The authors aimed to perform a meta-analysis to evaluate the association between herpes simplex virus (HSV) infection and the risk of developing dementia.

Methods

The authors searched the following databases: PubMed, Scopus, Cochrane Library, and Web of Science. The authors included any randomized control trials and controlled observational studies that investigated the prevalence of dementia in HSV-infected patients and HSV-free control group. Also, if the studies measured the levels of HSV antibodies and incidence of these antibodies in patients with dementia compared with a healthy control group.

Results

After a comprehensive literature search, 19 studies were included in the meta-analysis with 342 535 patients included in the analysis. The pooled analysis showed a statistically significant association between Alzheimer's disease (AD), mild cognitive impairment (MCI), and increased levels of IgG titer group [mean difference (MD) = 0.99, 95% confidence interval (CI) = 0.36-1.63, P-value = 0.002], (MD = 0.80, 95% CI = 0.26-1.35, P-value = 0.004), respectively. Additionally, the generic inverse variance showed a statistically significant association between the HSV group and increased incidence of dementia compared with the no HSV control group [risk ratio (RR) = 2.23, 95% CI = 1.18-2.29, P-value <0.00001]. Moreover, this analysis showed no statistically significant difference between the AD group and the control group in anti-HSV IgM titer n (%) outcome (RR = 1.35, 95% CI = 0.91-2.01, P-value = 0.14), respectively.

Conclusion

This study revealed that AD and MCI patients have increased levels of IgG antibodies titer against HSV infection. The study showed a significant association between HSV infection and increased incidence of dementia. Thus, regular follow-up of HSV patients' IgG titer levels could be useful in the prevention of dementia in these patients.

Longitudinal Effects of Herpesviruses on Multiple Cognitive Outcomes in Healthy Elderly Adults

BACKGROUND

Herpesviruses have been proposed to be involved in Alzheimer's disease development as potentially modifiable pathology triggers.

OBJECTIVE

To investigate associations of serum antibodies for herpes simplex virus (HSV)-1 and cytomegalovirus (CMV) and anti-herpesvirus treatment with cognitive outcomes in relation to interactions with APOE ɛ4.

METHODS

The study included 849 participants in the population-based Prospective Investigation of the Vasculature in Uppsala Seniors study. Cognitive performance at the ages of 75 and 80 years was assessed using the Mini-Mental State Examination (MMSE), trail-making test (TMT) A and B, and 7-minute screening test (7MS).

RESULTS

Anti- HSV-1 IgG positivity was associated cross-sectionally with worse performance on the MMSE, TMT-A, TMT-B, 7MS, enhanced free recall, and verbal fluency tests (p = 0.016, p = 0.016, p <  0.001, p = 0.001, p = 0.033, and p <  0.001, respectively), but not orientation or clock drawing. Cognitive scores did not decline over time and longitudinal changes did not differ according to HSV-1 positivity. Anti- CMV IgG positivity was not associated cross-sectionally with cognition, but TMT-B scores declined more in anti- CMV IgG carriers. Anti- HSV-1 IgG interacted with APOE ɛ4 in association with worse TMT-A and better enhanced cued recall. Anti- HSV IgM interacted with APOE ɛ4 and anti-herpesvirus treatment in association with worse TMT-A and clock drawing, respectively.

CONCLUSION

These findings indicate that HSV-1 is linked to poorer cognition in cognitively healthy elderly adults, including impairments in executive function, memory, and expressive language. Cognitive performance did not decline over time, nor was longitudinal decline associated with HSV-1.

Aβ plaques do not protect against HSV-1 infection in a mouse model of familial Alzheimer's disease, and HSV-1 does not induce Aβ 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 Aβ 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 Aβ aggregation, the current study examined whether Aβ 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 Aβ plaques in a mouse model of late-onset AD that does not develop Aβ pathology spontaneously. In aged 5XFAD mice infected via eye scarification, high density of Aβ 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 Aβ deposits, however, no association between HSV-1 and Aβ aggregates could be found. To test whether HSV-1 triggers Aβ aggregation in a mouse model that lacks spontaneous Aβ pathology, 13-month-old hAβ/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 Aβ 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 Aβ pathology.

Investigation of the association between the antibody responses to neurotropic viruses and dementia outcomes in the UK Biobank

The causes that trigger the onset of dementia are still unknown. Recently there has been an increasing interest in the possible role of infectious agents in the brain in the pathogenesis of this condition. Amongst the viruses, members of the Herpesviridae family, namely herpes simplex virus-1 (HSV1), cytomegalovirus (CMV), human herpesvirus-6 (HHV6), human herpesvirus-7 (HHV7) and varicella zoster virus (VZV) have been suggested as potential causes of the disease. However, the relative importance of these and other viruses in contributing to dementia remains unclear. We evaluated the association between seropositivity status of all viruses available in a large, population-based dataset (the UK Biobank) and dementia risk in an unbiased way. Of the 15 viruses investigated, our results showed a statistically significant increase of dementia risk associated only with HSV1 seropositivity (OR 2.14, 95% C.I. 1.21-3.81). However, by combining the data we found that seropositivity for 4 viruses (HSV1, HHV6, HHV7 and VZV) also significantly increases the risk of dementia (OR = 2.37, 95% C.I. 1.43-3.92). These four viruses have been described previously as neurotropic viruses. Our results provide support for a role for neurotropic viruses in the pathology of dementia.

The Hippocampal Vulnerability to Herpes Simplex Virus Type I Infection: Relevance to Alzheimer's Disease and Memory Impairment

Herpes simplex virus type 1 (HSV-1) as a possible infectious etiology in Alzheimer’s disease (AD) has been proposed since the 1980s. The accumulating research thus far continues to support the association and a possible causal role of HSV-1 in the development of AD. HSV-1 has been shown to induce neuropathological and behavioral changes of AD, such as amyloid-beta accumulation, tau hyperphosphorylation, as well as memory and learning impairments in experimental settings. However, a neuroanatomical standpoint of HSV-1 tropism in the brain has not been emphasized in detail. In this review, we propose that the hippocampal vulnerability to HSV-1 infection plays a part in the development of AD and amnestic mild cognitive impairment (aMCI). Henceforth, this review draws on human studies to bridge HSV-1 to hippocampal-related brain disorders, namely AD and aMCI/MCI. Next, experimental models and clinical observations supporting the neurotropism or predilection of HSV-1 to infect the hippocampus are examined. Following this, factors and mechanisms predisposing the hippocampus to HSV-1 infection are discussed. In brief, the hippocampus has high levels of viral cellular receptors, neural stem or progenitor cells (NSCs/NPCs), glucocorticoid receptors (GRs) and amyloid precursor protein (APP) that support HSV-1 infectivity, as well as inadequate antiviral immunity against HSV-1. Currently, the established diseases HSV-1 causes are mucocutaneous lesions and encephalitis; however, this review revises that HSV-1 may also induce and/or contribute to hippocampal-related brain disorders, especially AD and aMCI/MCI.

Herpes simplex virus, early neuroimaging markers and incidence of Alzheimer's disease

While previous studies suggest the implication of herpes simplex virus (HSV) in the onset of Alzheimer's disease (AD), no study has investigated its association with early neuroimaging markers of AD. In the Three-City and the AMI cohorts, the associations between HSV infection and (i) hippocampal volume (n = 349), (ii) white matter alterations in the parahippocampal cingulum and fornix using diffusion tensor imaging (n = 260), and (iii) incidence of AD (n = 1599) were assessed according to APOE4 status. Regardless of APOE4 status, infected subjects presented (i) significantly more microstructural alterations of the parahippocampal cingulum and fornix, (ii) lower hippocampal volumes only when their anti-HSV IgG level was in the highest tercile-reflecting possibly more frequent reactivations of the virus (p = 0.03 for subjects with a high anti-HSV IgG level while there was no association for all infected subjects, p = 0.19), and (iii) had no increased risk of developing AD. Nevertheless, among APOE4 carriers, infected subjects presented lower hippocampal volumes, although not significant (p = 0.09), and a two or three times higher risk of developing AD (adjusted Hazard ratio (aHR) = 2.72 [1.07-6.91] p = 0.04 for infected subjects and aHR = 3.87 [1.45-10.28] p = 0.007 for infected subjects with an anti-HSV IgG level in the highest tercile) while no association was found among APOE4 noncarriers. Our findings support an association between HSV infection and AD and a potential interaction between HSV status and APOE4. This reinforces the need to further investigate the infectious hypothesis of AD, especially the associated susceptibility factors and the possibility of preventive treatments.

Overwhelming Evidence for a Major Role for Herpes Simplex Virus Type 1 (HSV1) in Alzheimer's Disease (AD); Underwhelming Evidence against

This review describes investigations of specific topics that lie within the general subject of HSV1's role in AD/dementia, published in the last couple of years. They include studies on the following: relationship of HSV1 to AD using neural stem cells; the apparent protective effects of treatment of HSV1 infection or of VZV infection with antivirals prior to the onset of dementia; the putative involvement of VZV in AD/dementia; the possible role of human herpes virus 6 (HHV6) in AD; the seemingly reduced risk of dementia after vaccination with diverse types of vaccine, and the association shown in some vaccine studies with reduced frequency of HSV1 reactivation; anti-HSV serum antibodies supporting the linkage of HSV1 in brain with AD in APOE-ε4 carriers, and the association between APOE and cognition, and association of APOE and infection with AD/dementia. The conclusions are that there is now overwhelming evidence for HSV1's role-probably causal-in AD, when it is present in brain of APOE-ε4 carriers, and that further investigations should be made on possible prevention of the disease by vaccination, or by prolonged antiviral treatment of HSV1 infection in APOE-ε4 carriers, before disease onset.

Tissue Microbiome Associated With Human Diseases by Whole Transcriptome Sequencing and 16S Metagenomics

In recent years, a substantial number of tissue microbiome studies have been published, mainly due to the recent improvements in the minimization of microbial contamination during whole transcriptome analysis. Another reason for this trend is due to the capability of next-generation sequencing (NGS) to detect microbiome composition even in low biomass samples. Several recent studies demonstrate a significant role for the tissue microbiome in the development and progression of cancer and other diseases. For example, the increase of the abundance of Proteobacteria in tumor tissues of the breast has been revealed by gene expression analysis. The link between human papillomavirus infection and cervical cancer has been known for some time, but the relationship between the microbiome and breast cancer (BC) is more novel. There are also recent attempts to investigate the possible link between the brain microbiome and the cognitive dysfunction caused by neurological diseases. Such studies pointing to the role of the brain microbiome in Huntington’s disease (HD) and Alzheimer’s disease (AD) suggest that microbial colonization is a risk factor. In this review, we aim to summarize the studies that associate the tissue microbiome, rather than gut microbiome, with cancer and other diseases using whole-transcriptome analysis, along with 16S rRNA analysis. After providing several case studies for each relationship, we will discuss the potential role of transcriptome analysis on the broader portrayal of the pathophysiology of the breast, brain, and vaginal microbiome.

Interaction between APOE4 and herpes simplex virus type 1 in Alzheimer's disease

INTRODUCTION

Numerous results suggest the implication of infectious agents in the onset of Alzheimer's disease (AD).

METHODS

In the Bordeaux-3C prospective cohort, we assessed the impact of herpes simplex virus type 1 (HSV-1) infection on the incidence of AD according to apolipoprotein E (APOE) status, a genetic susceptibility factor. Cox models were performed to estimate the 10-year risk of AD associated with anti-HSV antibodies in 1037 participants according to APOE4 status.

RESULTS

Among APOE4 carriers, subjects for whom the frequency of HSV-1 reactivation is supposed to be high, that is, immunoglobulin M (IgM) positive or elevated levels of IgG, had an increased risk of AD with adjusted hazard ratios (HRs) of 3.68 (1.08-12.55) and 3.28 (1.19-9.03), respectively. No significant association was found in APOE4-negative subjects.

DISCUSSION

These results, in accordance with a solid pathophysiological rationale, suggest a role for HSV-1 in AD development among subjects with a genetic susceptibility factor, the APOE4 allele.

Immunoglobulin Genes and Immunity to HSV1 in Alzheimer's Disease

Although genome-wide association studies (GWAS) of late-onset Alzheimer's disease (AD) have identified numerous genes that influence the risk for disease, the majority of the genetic variance of AD remains uncharacterized. Furthermore, current GWAS, despite their name, do not evaluate all genes in the human genome. One such gene complex is immunoglobulin GM (γ marker) genes on chromosome 14. GM genes are excellent candidate genes for AD because they influence immunity to herpes simplex virus type 1 (HSV1), which has been implicated in AD pathology by an increasing number of reports. The aim of this investigation was to determine if particular GM genotypes were associated with AD and mild cognitive impairment (MCI), and whether they contributed to the interindividual differences in the level of anti-HSV1 IgG antibodies. A total of 141 HSV1 seropositive individuals-56 AD patients, 48 MCI individuals, and 37 sex- and age-matched healthy controls-were characterized for GM alleles 3, 17, and 23. The homozygosity for the GM 3 allele was significantly associated with MCI (p = 0.025). GM 3/17 heterozygous AD patients had significantly higher levels of anti-HSV1 antibodies than the healthy controls expressing the same genotype (p = 0.0004). Among MCI subjects, the GM 3/17 genotype was associated with significantly higher level of anti-HSV1 antibodies as compared to the GM 17/17 homozygous genotype (pc = 0.040). Among AD patients, the GM 23+/-genotype was significantly associated with anti-HSV1 antibody responses (pc = 0.025). These results suggest that GM genes could act as potential unifiers of the genetic and viral etiology of AD.

Relation between FCGRIIB rs1050501 and HSV-1 specific IgG antibodies in Alzheimer's disease

Background

Alzheimer’s Disease (AD) is a chronic neurodegenerative disorder characterized by extracellular plaques, intracellular neurofibrillary tangles and neuronal loss in the central nervous system (CNS). Pathogens are suspected to have a role in the development of AD; herpes simplex virus type 1 (HSV-1), in particular, is suggested to be a risk factor for the disease. The gamma receptor for the Fc portion of IgG molecules (FCGRs) plays a crucial role in regulating immune responses, and among FCGRs, FCGRIIB is endowed with an inhibitory function. Notably, the rs1050501 polymorphism of FCGRIIB gene associates with autoimmune diseases and with neuronal uptake and interneuronal accumulation of amyloid beta in animal AD models.

Methods

Genotype and allelic distribution of ApoE4 and FCGRIIB rs1050501 were evaluated in a case–control population of 225 AD patients, 93 MCI individuals and 201 sex and age matched healthy controls (HC). HSV-1 total IgG titers and IgG subclasses were detected and quantified in a subgroup of the main study population by ELISA.

Results

Genotype and allelic distribution of FCGRIIB was comparable in the study population. HSV-1-specific antibody titers were significantly higher in AD and MCI compared to HC (p < 0.01 for both); IgG3 titers, in particular, were increased in MCI compared to AD (p = 0.04). Analyses of possible correlations between the FCGRIIB rs1050501 genotype polymorphism and IgG subclasses showed that the presence of IgG3 was more frequent in MCI carrying the FCGRIIB TT (94.1%) compared to those carrying the CT genotype (63.6%) (p = 0.03).

Conclusion

Results herein show an association between humoral immune response against HSV-1 and FCGRIIB rs1050501 genetic variation in the first stage of the disease.

HSV-1-Specific IgG3 Titers Correlate with Brain Cortical Thinning in Individuals with Mild Cognitive Impairment and Alzheimer's Disease

Repeated reactivations of latent herpes simplex virus type-1 (HSV-1) in the central nervous system (CNS) may contribute to neurodegeneration in Alzheimer’s disease (AD) patients. Immune response is a key element for the control of viral reactivation. HSV-1 uses a number of strategies to evade immune recognition, Immunoglobulin G 3 (IgG₃) alone counteracts humoral immunoevasion, as it is the only IgG subclass that is not blocked by the HSV-1 Fc receptor, a protein that protects virion and infected cells from antibody-mediated effector mechanisms. We examined HSV-1-specific IgG₃ titers in serum of AD (n = 70) and mild cognitive impairment (MCI) (n = 61) subjects comparing the results to those of 67 age- and sex-matched healthy controls (HC); associations between MRI-determined brain cortical health and HSV-1-specific IgG₃ were analyzed in a subgroup of AD and MCI subjects. HSV-1-specific IgG₃ were more frequently detected in MCI compared to AD and HC subjects. Significant inverse correlations were found between IgG₃ titers and brain cortical thickness in areas typically involved in dementia and HSV-1 encephalitis in AD patients; interestingly, this negative correlation was much less important in MCI subjects. All together these results suggest that in AD an inefficient IgG₃ humoral immune response, failing to block viral replication, contributes to progressive neurodegeneration.

Herpes Simplex Virus-1 in the Brain: The Dark Side of a Sneaky Infection

Herpes simplex virus-1 (HSV-1) establishes latency preferentially in sensory neurons of peripheral ganglia. A variety of stresses can induce recurrent reactivations of the virus, which spreads and then actively replicates to the site of primary infection (usually the lips or eyes). Viral particles produced following reactivation can also reach the brain, causing a rare but severe form of diffuse acute infection, namely herpes simplex encephalitis. Most of the time, this infection is clinically asymptomatic. However, it was recently correlated with the production and accumulation of neuropathological biomarkers of Alzheimer's disease. In this review we discuss the different cellular and molecular mechanisms underlying the acute and long-term damage caused by HSV-1 infection in the brain.

SERS-based biosensor for Alzheimer disease evaluation through the fast analysis of human serum

Alzheimer disease (AD) is the most common form of dementia in the elderly, progressively affecting the cognitive functions with a complex diagnostic procedure that limits the time for a prompt intervention. In this study we optimized a reliable protocol for the analysis of AD patients and healthy subjects' serum using the Surface Enhanced Raman Spectroscopy (SERS), taking into consideration the effect of different variables on the final spectra, analyzed and compared through multivariate analysis and correlated with hippocampus volume. As results, we demonstrated a statistical difference between the spectra collected from the two investigated groups, with an accuracy, precision and specificity of respectively 83%, 86%, and 86%. The correlation of these data with those obtained from MRI, demonstrated a direct correlation between Raman spectra and hippocampus degeneration showing the Raman Spectroscopy (RS) as a potential tool for the monitoring of AD progression and rehabilitation treatments.

Gold Nanoparticles Crossing Blood-Brain Barrier Prevent HSV-1 Infection and Reduce Herpes Associated Amyloid-βsecretion

Infections caused by HSV-1 and their typical outbreaks invading the nervous system have been related to neurodegenerative diseases. HSV-1 infection may deregulate the balance between the amyloidogenic and non-amyloidogenic pathways, raising the accumulation of amyloid-β peptides, one of the hallmarks in the neurodegenerative diseases. An effective treatment against both, HSV-1 infections and neurodegeneration, is a major therapeutic target. Therefore, gold nanoparticles (NPAus) have been previously studied in immunotherapy, cancer and cellular disruptions with very promising results. Our study demonstrates that a new NPAus family inhibits the HSV-1 infection in a neural-derived SK-N-MC cell line model and that this new NPAus reduces the HSV-1-induced β-secretase activity, as well as amyloid-β accumulation in SK-APP-D1 modifies cell line. We demonstrated that NPAuG3-S8 crosses the blood-brain barrier (BBB) and does not generate cerebral damage to in vivo CD1 mice model. The NPAuG3-S8 could be a promising treatment against neuronal HSV-1 infections and neuronal disorders related to the Aβ peptides.

Herpes simplex virus-1 (HSV-1) infection induces a potent but ineffective IFN-λ production in immune cells of AD and PD patients

Background

The sequential activation of immediate early (IE), early (E) and late (L) genes is required to allow productive herpes simplex virus type 1 (HSV-1) infection. Several evidences suggest that, together with inflammation, an immunological response incapable to counteract HSV-1 reactivation plays a role in the pathogenesis of Alzheimer’s (AD) and Parkinson’s (PD) diseases. IFN-lambda (IFN-λ), a cytokine endowed with a robust antiviral activity, contains HSV-1 reactivation. HSV-1-induced IFN-λ, IL-10 and IL-1β as well as the expression of viral IE, E and L genes were analyzed in vitro in peripheral blood mononuclear cells (PBMC) of AD and PD patients as well as of healthy controls (HC).

Methods

PBMC of AD, PD and HC were in vitro infected with one multiplicity of infection (1 MOI) HSV-1. IE, E, and L viral genes transcription as well as IFN-λ, IL-10 and IL-1β production were analyzed.

Results

In HSV-1-infected cells of AD and PD patients compared to HC: (1) transcription of IE (ICP0, ICP27) genes was reduced whereas that of E (UL41, UL29) and L (UL48, LAT) genes was increased; (2) IFN-λ mRNA expression was increased. IL-1β was augmented and IL-10 was reduced in unstimulated cells of AD and PD compared to HC; HSV-1 infection significantly increased IL-10 production in HC alone.

Conclusions

Data herein show that a proinflammatory condition is present in AD and PD, in whom attempts to obstacle viral replication via an initial, possibly more potent IFN-λ-mediated control of IE viral genes is unsuccessful.

HSV-1-Specific IgG Subclasses Distribution and Serum Neutralizing Activity in Alzheimer's Disease and in Mild Cognitive Impairment

Human Herpes Simplex Virus type 1 (HSV-1) infection is suggested to play a role in the development of Alzheimer's disease (AD). Immunoglobulin G (IgG) neutralize HSV-1 activity, but the virus can evade IgG-mediated immune responses by expressing receptor that efficiently binds the Fc portion of all IgG subclasses with the exception of IgG3. We analyzed HSV-1-specific IgG subclasses and IgG-mediated serum neutralization activity against HSV-1 in individuals with a diagnosis of either AD or mild cognitive impairment (MCI), comparing the results with those obtained in age-matched healthy controls (HC). 186 individuals were enrolled in the study: 67 AD, 58 MCI, and 61 HC. HSV-1 IgG titers and subclasses, neutralizing antibody (NAb) titers, and complement C3 concentration-critical component of antibody-mediated effector activity-were measured in sera by ELISA; IgG neutralizing activity was performed on HSV-1 infected Vero cells. Results showed that, whereas HSV-1-specific IgG1, IgG2, and IgG4 titers as well as complement C3 serum concentration were comparable in all groups of individuals, IgG3 were more frequently detected in MCI (89%) compared to AD (75%; p < 0.05) and HC (68%; p = 0.003), whereas the titer is similar among the three groups (AD: 0.66±0.21 OD; MCI: 0.68±0.24 OD; HC: 0.72±0.28 OD). Notably, HSV-1 specific neutralizing ability of AD sera was reduced even in the presence of high quantity of IgG3. As IgG3 plays a key role in counteracting the ability of HSV-1 to evade immune responses, these data reinforce the hypothesis of a pathogenetic role of HSV-1 in AD.

Herpes simplex virus type 1 and Alzheimer's disease: link and potential impact on treatment

Introduction: Alzheimer's disease (AD), the most common form of dementia worldwide, is a multifactorial disease with a still unknown etiology. Herpes simplex virus 1 (HSV-1) has long been suspected to be one of the factors involved in the pathogenesis of the disease. Areas covered: We review the literature focusing on viral characteristics of HSV-1, the mechanisms this virus uses to infect neural cells, its interaction with the host immune system and genetic background and summarizes results and research that support the hypothesis of an association between AD and HSV-1. The possible usefulness of virus-directed pharmaceutical approaches as potential treatments for AD will be discussed as well. Expert opinion: We highlight crucial aspects that must be addressed to clarify the possible role of HSV-1 in the pathogenesis of the disease, and to allow the design of new therapeutical approaches for AD.

Herpesviral infections and antimicrobial protection for Alzheimer's disease: Implications for prevention and treatment

Accumulating evidence suggests that infections by herpesviruses might be closely linked to Alzheimer's disease (AD). Pathological hallmarks of AD brains include senile plaques induced by amyloid β peptide (Aβ) in the extracellular space and intracellular neurofibrillary tangles (NFTs) consisting of phosphorylated tau protein. The prevailing hypothesis for the mechanism of AD is amyloid cascade reaction. Recent studies revealed that infections by herpesviruses induce the similar pathological hallmarks of AD, including Aβ production, phosphorylation of tau (P-tau), oxidative stress, neuroinflammation, etc. Aβ peptide is regarded as one of the antimicrobial peptides, which inhibits HSV-1 replication. In the elderly, reactivation of herpesviruses might act as an initiator for amyloid cascade reaction in vulnerable individuals, triggering the neurofibrillary formation of phosphorylated tau and inducing oxidative stress and neuroinflammation, which can further contribute to the accumulation of Aβ and P-tau by impairing mitochondria and autophagosome. Epidemiological studies have shown AD susceptibility genes, such as APOE-ε4 allele, are highly linked to infections by herpesviruses. Interestingly, anti-herpesviral therapy significantly reduced the risk of AD in a large population study. Given that herpesviruses are arguably the most prevalent opportunistic pathogens and often reactivate in the elderly, it is reasonable to argue reactivation of herpesviruses might be major culprits for initiating AD in individuals carrying AD susceptibility genes. In this review, we summarize epidemiological and molecular evidence that support for a hypothesis of herpesviral infections and antimicrobial protection in the development of AD, and discuss the implications for future prevention and treatment of the disease.

The PILRA G78R Variant Correlates with Higher HSV-1-Specific IgG Titers in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by a progressive decline in cognitive performance; Mild Cognitive Impairment (MCI) is instead an objective decline in cognitive performance that does not reach pathology. Paired immunoglobulin-like type 2 receptor alpha (PILRA) is a cell surface inhibitory receptor that was recently suggested to be involved in AD pathogenesis. In particular, the arginine-to-glycine substitution in position 78 (R78, rs1859788) was shown to be protective against AD. Herpes simplex virus type 1 (HSV-1) infection is suspected as well to be involved in AD. Interestingly, HSV-1 uses PILRA to infect cells, and HSV-1 infects more efficiently PIRLA G78 compared to R78 macrophages. We analyzed PILRA rs1859788 polymorphism and HSV-1 humoral immune responses in AD (n = 61) and MCI patients (n = 48), and in sex and age matched healthy controls (HC; n = 57). The rs1859788 PILRA genotype distribution was similar among AD, MCI and HC; HSV-1 antibody (Ab) titers were increased in AD and MCI compared to HC (p < 0.05 for both comparisons). Notably, HSV-1-specific IgG1 were significantly increased in AD patients carrying PILRA R78 rs1859788 AA than in those carrying G78 AG or GG (p = 0.01 for both comparisons), and the lowest titers of HSV-1-specific IgG1 were observed in rs1859788 GG AD. HSV-1 IgG are increased in AD patients with the protective R78 PILRA genotype. Because in AD patients brain atrophy is inversely correlated with HSV-1-specific IgG titers, results herein suggest a possible link between two important genetic and infective factors suspected to be involved in AD pathogenesis.

Human herpesvirus infections and dementia or mild cognitive impairment: a systematic review and meta-analysis

Interest is growing in the role of infectious agents in the pathogenesis of dementia, but current evidence is limited. We conducted a systematic review and meta-analysis to investigate the effect of any of eight human herpesviruses on development of dementia or mild cognitive impairment (MCI). We searched the Cochrane Library, Embase, Global Health, Medline, PsycINFO, Scopus, Web of Science, clinical trials registers and grey literature sources from inception to December 2017 for observational studies with cohort, case control or self-controlled designs, or randomised controlled trials of interventions against herpesviruses. Pooled effect estimates and 95% confidence intervals (CIs) were generated through random effects meta-analyses across studies with the same design, outcome, and virus type, method and site of measurement. We included 57 studies across various geographic settings. Past infection with herpesviruses, measured by IgG seropositivity, was generally not associated with dementia risk. A single cohort study rated moderate quality showed an association between varicella zoster virus reactivation (ophthalmic zoster) and incident dementia (HR 2.97; 95%CI, 1.89 to 4.66). Recent infection with, or reactivation of, herpes simplex virus type 1 or type 1/2 unspecified, cytomegalovirus and human herpes virus-6 measured by serum IgM, high titre IgG or clinical disease may be associated with dementia or MCI, though results were inconsistent across studies and overall evidence rated very low quality. Longitudinal population studies with robust repeated virus measurements taken sufficiently proximal to dementia onset are needed to establish whether, when and among whom herpesviruses affect dementia risk.

Urea dilution of serum for reproducible anti-HSV1 IgG avidity index

BACKGROUND

Herpes simplex virus type 1 (HSV1), establishes life-long latency and can cause symptoms during both first-time infection and later reactivation. The aim of the present study was to describe a protocol to generate a reliable and discriminative avidity index (AI) for anti-HSV1 IgG content in human sera.

METHODS

Human serum from two distinct cohorts; one a biobank collection (Betula) (n = 28), and one from a clinical diagnostics laboratory at Northern Sweden University Hospital (NUS) (n = 18), were assessed for presence of IgG antibodies against HSV1 by a commercially available ELISA-kit. Addition of urea at the incubation step reduces effective binding, and the ratio between urea treated sample and non-treated sample was used to express an avidity index (AI) for individual samples.

RESULTS

AI score ranged between 43.2 and 73.4% among anti-HSV1 positive biobank sera. Clinical samples ranged between 36.3 and 74.9%. Reproducibility expressed as an intraclass correlation coefficient (ICC) was estimated at 0.948 (95% CI: 0.900-0.979) and 0.989 (95% CI 0.969-0.996) in the biobank and clinical samples, respectively.

CONCLUSION

The method allows for AI scoring of anti-HSV1 IgG from individual human sera with a single measurement. The least significant change between two measurements at the p < 0.05 level was estimated at 5.4 and 3.2 points, respectively, for the two assessed cohorts.

Viral Hypothesis and Antiviral Treatment in Alzheimer's Disease

PURPOSE OF REVIEW

Viruses, particularly herpes simplex virus (HSV), may be a cause of Alzheimer's disease (AD). The evidence supporting the viral hypothesis suggests that antiviral treatment trials, which have not been conducted, are warranted.

RECENT FINDINGS

HSV1 (oral herpes) and HSV2 (genital herpes) can trigger amyloid aggregation, and their DNA is common in amyloid plaques. HSV1 reactivation is associated with tau hyperphosphorylation and possibly tau propagation. Anti-HSV drugs reduce Aβ and p-tau accumulation in infected mouse brains. Clinically, after the initial oral infection, herpes simplex virus-1 (HSV1) becomes latent in the trigeminal ganglion and recurrent reactivation may produce neuronal damage and AD pathology. Clinical studies show cognitive impairment in HSV seropositive patients, and antiviral drugs show strong efficacy against HSV. An antiviral treatment trial in AD is clearly warranted. A phase II treatment trial with valacyclovir, an anti-HSV drug, recently began with evaluation of clinical and biomarker outcomes.

Ancient oncogenesis, infection and human evolution

The recent discovery that malignant neoplastic lesions date back nearly 2 million years ago not only highlights the antiquity of cancer in the human lineage, but also provides remarkable insight into ancestral hominin disease pathology. Using these Early Pleistocene examples as a point of departure, we emphasize the prominent role of viral and bacterial pathogens in oncogenesis and evaluate the impact of pathogens on human evolutionary processes in Africa. In the Shakespearean vernacular "what's past is prologue," we highlight the significance of novel information derived from ancient pathogenic DNA. In particular, and given the temporal depth of human occupation in sub-Saharan Africa, it is emphasized that the region is ideally positioned to play a strategic role in the discovery of ancient pathogenic drivers of not only human mortality, but also human evolution. Ancient African pathogen genome data can provide novel revelations concerning human-pathogen coevolutionary processes, and such knowledge is essential for forecasting the ways in which emerging zoonotic and increasingly transmissible diseases might influence human demography and longevity in the future.

Immune and Imaging Correlates of Mild Cognitive Impairment Conversion to Alzheimer's Disease

Amnestic mild cognitive impairment (aMCI) conversion to Alzheimer’s disease (AD) is seen in a sizable portion of aMCI patients; correlates predicting such conversion are poorly defined but neuroinflammation and the reactivation of chronic viral infections are suspected to play a role in this phenomenon. We analyzed these aspects in two homogeneous groups of aMCI who did or did not convert to AD over a 24-months period. Results showed that at baseline in those aMCI individuals who did not convert to AD: 1) Aβ_1-42 stimulated production of the pro-inflammatory cytokines IL6 and IL1β by CD14⁺ cells was significantly reduced (p = 0.01), 2) CD14⁺/IL-33⁺ cells were increased (p = 0.0004); 3) MFI of TLR8 and TLR9 was significantly increased, and 4) better preserved hippocampus volumes were observed and correlated with IL33⁺/CD14⁺ cells. Notably, Aβ_1-42 stimulated production of the antiviral cytokine IFN-λ was increased as well in non-AD converters, although with a borderline statistical significance (p = 0.05). Data herein indicating that proinflammatory cytokines are reduced, whereas IFN-λ production and TLR8 and 9 MFI are augmented in those aMCI in whom AD conversion is not observed suggest that the ability to mount stronger antiviral response within an antiiflammatory milieu associates with lack of AD conversion.

Neuroinflammation and Infection: Molecular Mechanisms Associated with Dysfunction of Neurovascular Unit

Neuroinflammation is a complex inflammatory process in the central nervous system, which is sought to play an important defensive role against various pathogens, toxins or factors that induce neurodegeneration. The onset of neurodegenerative diseases and various microbial infections are counted as stimuli that can challenge the host immune system and trigger the development of neuroinflammation. The homeostatic nature of neuroinflammation is essential to maintain the neuroplasticity. Neuroinflammation is regulated by the activity of neuronal, glial, and endothelial cells within the neurovascular unit, which serves as a “platform” for the coordinated action of pro- and anti-inflammatory mechanisms. Production of inflammatory mediators (cytokines, chemokines, reactive oxygen species) by brain resident cells or cells migrating from the peripheral blood, results in the impairment of blood-brain barrier integrity, thereby further affecting the course of local inflammation. In this review, we analyzed the most recent data on the central nervous system inflammation and focused on major mechanisms of neurovascular unit dysfunction caused by neuroinflammation and infections.

Modulation of Immune Responses to Herpes Simplex Virus Type 1 by IFNL3 and IRF7 Polymorphisms: A Study in Alzheimer's Disease

Herpes simplex virus type 1 (HSV-1) has long been suspected to play a role in Alzheimer's disease (AD), the most common form of dementia. IFN-lambda (IFN-λ) is one of the key cytokine in innate antiviral defenses and, in particular, has an appreciable antiviral activity against HSV-1 infection. IFN-λ expression is regulated by the interaction between two different proteins: Mediator Complex 23 (MED23) and Interferon-Responsive Transcription Factor 7 (IRF7); single nucleotide polymorphisms (SNPs) in these genes as well as in IFNL3 were shown to be differently distributed in AD patients. In this study, allelic discrimination analysis for IFNL3 rs12979860, MED23 rs3756784, and IRF7 rs6598008, as well as IFN-λ serum concentration and anti-HSV-1 antibody (Ab) titers were performed in 79 AD patients, 57 mild cognitive impairment (MCI) individuals, and 81 healthy controls (HC) who were HSV-1-seropositive. Results showed that INF-λ serum concentration was increased in AD and MCI carrying the IFNL3 T allele compared to HC (AD versus HC: p = 0.014; MCI versus HC: p = 0.029), with the highest anti-HSV-1 Ab titers seen in AD patients carrying the IFNL3 CC genotype (p = 0.012 versus HC). Notably, anti-HSV-1 Ab titers were higher in AD and MCI individuals carrying the IRF7 AA genotype compared to HC (p = 0.018 for both). MED23 polymorphisms did not show any statistical association either with serum IFN-λ or with anti-HSV-1 Ab. Data herein suggest that the IFNL3 rs12979860 and IRF7 rs6598008 polymorphisms modulate immune responses against HSV-1 via their effect on the IFN-λ pathway. These results help to clarify the possible role of HSV-1 infection in AD pathogenesis.

A future perspective on neurodegenerative diseases: nasopharyngeal and gut microbiota

Neurodegenerative diseases are considered a serious life-threatening issue regardless of age. Resulting nerve damage progressively affects important activities, such as movement, coordination, balance, breathing, speech and the functioning of vital organs. Reports on the subject have concluded that neurodegenerative disease can be caused by mutations of susceptible genes, alcohol consumption, toxins, chemicals and other unknown environmental factors. Although several diagnostic techniques can be used to determine aetiologies, the process is difficult and often fails. Research shows that nasopharyngeal and gut microbiota play important roles in brain to spinal cord coordination. However, no conclusive epidemiologic evidence is available on the roles played by respiratory and gut microbiota in the development of neurodegenerative diseases. Thus, understanding the connection between respiratory and gut microbiota and the nervous system could provide information on causal links. The present review describes future perspectives on the role played by nasopharyngeal and gut microbiota in the development of neurodegenerative diseases.

High avidity HSV-1 antibodies correlate with absence of amnestic Mild Cognitive Impairment conversion to Alzheimer's disease

Amnestic Mild Cognitive Impairment (aMCI) is an alteration in cognitive abilities that can progress to Alzheimer's disease (AD), a condition in which herpes simplex type 1 (HSV-1) infection might play a pathogenetic role. Prognostic indexes capable of predicting aMCI conversion to AD are only partially understood. The objective of the present work is to verify whether HSV-1 immune responses is involved in conversion of aMCI to AD and correlate with grey matter brain morphometry. Two homogeneous groups of individuals who did or did not convert to AD over a 24-months period were selected after retrospective analysis of a cohort of patients with a diagnosis of aMCI. The selection of subjects was based on: a) clinical follow-up; b) neurocognitive evaluation at baseline and after 24months; c) availability of serum and DNA samples at baseline. 36 aMCI individuals, 21 of whom did (aMCI-converters) and 15 of whom did not (aMCI-non-converters) convert to AD, were included in the study. HSV-1 antibody (Ab) titers, avidity index and APOE genotyping were performed in all the enrolled individuals at baseline. Brain magnetic resonance imaging (MRI) by 1.5T scanner results at baseline were available as well in most (29/36) of these individuals. HSV-1-specific Ab titers were increased at baseline in aMCI-non-converters, and the avidity of these Ab was significantly higher in aMCI-non-converter compared to aMCI-converter (p=0.0018). Receiver operating characteristics analysis showed that HSV-1 avidity had a predictive value in distinguishing between aMCI-non-converters and aMCI-converters (p<0.0001). Notably, a positive correlation was detected as well between HSV-1 antibody titers and MRI-evaluated cortical volumes in the left hippocampus and amigdala (p_corr<0.05). In conclusion, stronger HSV-1-specific humoral responses associate with protection against AD conversion and better-preserved cortical volumes. These results reinforce the hypothesis for a role for HSV-1 in the pathogenesis of AD.

Lack of evidence for a role of HHV-6 in the pathogenesis of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD), the most common form of dementia worldwide, is associated with impairment in the mechanisms of the clearing of amyloid-β within a scenario of neuroinflammation. The etiopathogenesis of the AD is unclear, but a role for viral infection is suspected to play a role in initiating the disease. We recently described a positive correlation between high titers of HSV-1-specific antibodies (Ab) and the volumes of brain regions typically affected in disease.

OBJECTIVE

The exploration of a possible role for Herpesviridae in AD was extended by analyzing HHV-6-specific humoral immunity in individuals with AD or a diagnosis of amnestic mild cognitive impairment (aMCI), a condition that is often prodromic of the development of AD.

METHODS

59 AD, 60 aMCI, and 61 age-matched healthy controls were enrolled in the study. Serum HHV-6 IgG antibody titers and avidity index were tested by ELISA. Two randomly selected subgroups of AD and aMCI in whom HHV-6 serum antibodies were detected underwent brain magnetic resonance imaging (MRI) by 1.5 T scanner.

RESULTS

HHV-6 seroprevalence, antibody titers, and avidity were similar in the three groups. No correlation was found between Ab titers or avidity and brain volumes, either overall or in the regions typically affected by disease.

CONCLUSIONS

The lack of any relation between humoral immune response against HHV-6 and AD and aMCI seems to rule out a role for this virus in the pathogenesis of AD.

Herpes Simplex Virus type-1 infection induces synaptic dysfunction in cultured cortical neurons via GSK-3 activation and intraneuronal amyloid-β protein accumulation

Increasing evidence suggests that recurrent Herpes Simplex Virus type 1 (HSV-1) infection spreading to the CNS is a risk factor for Alzheimer’s Disease (AD) but the underlying mechanisms have not been fully elucidated yet. Here we demonstrate that in cultured mouse cortical neurons HSV-1 induced Ca²⁺-dependent activation of glycogen synthase kinase (GSK)-3. This event was critical for the HSV-1-dependent phosphorylation of amyloid precursor protein (APP) at Thr668 and the following intraneuronal accumulation of amyloid-β protein (Aβ). HSV-1-infected neurons also exhibited: i) significantly reduced expression of the presynaptic proteins synapsin-1 and synaptophysin; ii) depressed synaptic transmission. These effects depended on GSK-3 activation and intraneuronal accumulation of Aβ. In fact, either the selective GSK-3 inhibitor, SB216763, or a specific antibody recognizing Aβ (4G8) significantly counteracted the effects induced by HSV-1 at the synaptic level. Moreover, in neurons derived from APP KO mice and infected with HSV-1 Aβ accumulation was not found and synaptic protein expression was only slightly reduced when compared to wild-type infected neurons. These data further support our contention that HSV-1 infections spreading to the CNS may contribute to AD phenotype.