A critical role for induced IgM in the protection against West Nile virus infection

Persistent splenic-derived IgMs preferentially recognize factor VIII A2 and C2 domain epitopes but do not alter antibody production

BACKGROUND

The most significant treatment complication for patients with hemophilia A is the development of neutralizing immunoglobins (Igs) G, termed inhibitors, against factor VIII (FVIII), which prevent FVIII replacement therapy. Low titers of FVIII-specific IgMs have been identified in hemophilia A patients with and without inhibitors, as well as in healthy individuals. However, the duration and influence of IgMs on the immune response to FVIII remains unclear.

OBJECTIVES

To characterize the binding interactions of persistently secreted FVIII-specific IgMs in hemophilia A mice and assess their effect on IgG antibody development.

METHODS

Splenic-derived monoclonal antibodies (mAbs) from immunized FVIII knockout mice were isolated and purified using hybridoma technology. Binding interactions were assessed utilizing a novel fluid-phase enzyme-linked immunosorbent assay and computational modeling with High Ambiguity-Driven protein-protein DOCKing to account for weak IgM binding.

RESULTS

Sixteen porcine cross-reactive and noninhibitory FVIII-specific IgM mAbs were identified. RNA sequencing of FVIII-specific IgMs revealed 13 unique variable, diversity, and joining (VDJ)/variable and joining (VJ) sequences indicating derivation from 13 unique B cell clones. The IgMs demonstrated polyclonal and polyreactive binding to FVIII in vitro and in silico. Molecular docking studies with reconstructed IgM variable, diversity, and joining/variable and joining regions identified frequent IgM interactions with amino acid residues K376, T381, K437, R2215, or K2249 within the FVIII A2 and C2 domains. Injections of individual IgMs prior to FVIII exposure and co-injection of FVIII/IgM immune complexes did not affect de novo FVIII antibody production.

CONCLUSION

Persistent FVIII-specific IgMs are polyclonal but preferentially bind the A2 and C2 domains. FVIII/IgM immune complex formation does not significantly alter inhibitor development.

Ocular manifestations of West Nile virus infection: A case report and systematic review of the literature

PURPOSE

To report the case of a patient with ocular West Nile virus infection (WNVI) and to describe the demographics, eye characteristics, and treatment of patients with WNVI reported in the literature.

METHODS

Systematic literature search using the PubMed MEDLINE database searching for all cases of ocular WNVI published from inception until October 14, 2023. Inclusion criteria were patients with serologic and/or cerebrospinal fluid diagnosis of WNVI with ocular involvement.

RESULTS

A total of 60 patients (111 eyes), including the present case, were included. Most patients were males (57%), diagnosed in the United States (77%), and with a mean age at presentation of 54 years. The median time elapsed between the viral prodrome, and eye symptoms was 7 days. Neurologic involvement was present in 47 (78%) patients. Diabetes mellitus was the most frequent systemic comorbidity (45%). Posterior segment findings were present in 107 (96%) eyes. Multifocal chorioretinal lesions (86%), vitreous inflammation (51%), intraretinal hemorrhages (43%), and retinal vasculitis (21%) were the most frequent findings. Fluorescein angiography was performed in 88 (79%) eyes. Fifty-seven (51%) eyes did not receive treatment. Topical and systemic steroids were prescribed to 35% and 28% of eyes, respectively.

CONCLUSION

WNVI should be considered as a potential diagnosis in older patients who exhibit posterior uveitis, especially if they have recently experienced flu-like symptoms and have been exposed to mosquitoes. A comprehensive ocular assessment, which includes a dilated fundus examination and ocular imaging studies, can help raise suspicion for this condition even before serological confirmation is obtained.

Undiagnosed West Nile virus lineage 2d infection in a febrile patient from South-west Uganda, 2018

We report the retrospective identification and subsequent recovery of a near-complete West Nile Virus lineage 2 genomes from a hospitalized patient with acute febrile illness in Uganda, using a combination of degenerate primer polymerase chain reaction screening and a novel 1200bp nanopore-based whole-genome amplicon sequencing scheme. This represents the first West Nile virus genome to be recovered from a human in Uganda since its discovery in 1937. Basic molecular rather than serological surveillance methods could be more widely deployed in the region to better diagnose febrile infections.

Knowns and unknowns of TiLV-associated neuronal disease

Tilapia Lake Virus (TiLV) is associated with pathological changes in the brain of infected fish, but the mechanisms driving the virus's neuropathogenesis remain poorly characterized. TiLV establishes a persistent infection in the brain of infected fish even when the virus is no longer detectable in the peripheral organs, rendering therapeutic interventions and disease management challenging. Moreover, the persistence of the virus in the brain may pose a risk for viral reinfection and spread and contribute to ongoing tissue damage and neuroinflammatory processes. In this review, we explore TiLV-associated neurological disease. We discuss the possible mechanism(s) used by TiLV to enter the central nervous system (CNS) and examine TiLV-induced neuroinflammation and brain immune responses. Lastly, we discuss future research questions and knowledge gaps to be addressed to significantly advance this field.

Lessons Learned from West Nile Virus Infection:Vaccinations in Equines and Their Implications for One Health Approaches

Humans and equines are two dead-end hosts of the mosquito-borne West Nile virus (WNV) with similar susceptibility and pathogenesis. Since the introduction of WNV vaccines into equine populations of the United States of America (USA) in late 2002, there have been only sporadic cases of WNV infection in equines. These cases are generally attributed to unvaccinated and under-vaccinated equines. In contrast, due to the lack of a human WNV vaccine, WNV cases in humans have remained steadily high. An average of 115 deaths have been reported per year in the USA since the first reported case in 1999. Therefore, the characterization of protective immune responses to WNV and the identification of immune correlates of protection in vaccinated equines will provide new fundamental information about the successful development and evaluation of WNV vaccines in humans. This review discusses the comparative epidemiology, transmission, susceptibility to infection and disease, clinical manifestation and pathogenesis, and immune responses of WNV in humans and equines. Furthermore, prophylactic and therapeutic strategies that are currently available and under development are described. In addition, the successful vaccination of equines against WNV and the potential lessons for human vaccine development are discussed.

Rehabilitation Outcomes in Multiple Sclerosis Patients on Ocrelizumab Diagnosed With West Nile Virus Encephalitis

Multiple sclerosis (MS) has a global prevalence exceeding two million people and is a leading cause of non-traumatic physical disability. MS can be treated with ocrelizumab, an anti-CD20 monoclonal antibody. West Nile virus (WNV) is the most common cause of mosquito-borne viral encephalitis in North America. It can lead to neuroinvasive WNV disease (WNND) affecting the brain and peripheral nervous system, especially in immunocompromised patients, such as those being treated with ocrelizumab for MS. WNND is exceedingly rare and reported in less than 1% of cases of WNV. It has been established that inpatient rehabilitation improves functional outcomes in patients with MS and those with WNND. However, the inpatient rehabilitation outcomes in patients diagnosed with both WNND and MS have not been reported. In this study, we aimed to examine the rehabilitation outcomes of MS patients on ocrelizumab diagnosed with WNND. We performed a retrospective chart review of patients with MS treated with ocrelizumab, who were diagnosed with WNND and admitted to a single facility. Rehabilitation outcomes were assessed using functional independence measure (FIM) scores on admission and discharge. Three patients met the inclusion criteria; two in acute rehab, and one in the long-term acute care hospital (LTACH). Both patients admitted to acute inpatient rehabilitation showed an improvement in FIM scores from admission to discharge, one patient from 9 to 16 and the other from 14 to 54. However, the patient admitted to the LTACH had no improvement in FIM score from admission to discharge. Patients admitted to acute rehab were ultimately discharged home, while the patient admitted to the LTACH required discharge to a subacute rehabilitation facility. Based on our findings, intense and prolonged comprehensive inpatient rehabilitation is associated with improved functional outcomes and increased likelihood of discharge to home in this population suffering from both central and peripheral nervous system involvement due to MS and WNND.

Borrelia burgdorferi Infection-Induced Persistent IgM Secretion Controls Bacteremia, but Not Bacterial Dissemination or Tissue Burden

Infection with Borrelia burgdorferi causes Lyme disease in humans. In small rodents, the natural reservoir species of this spirochete, infections lead to only modest disease manifestations, despite causing persistence infection. Although B cell responses are central for controlling bacterial tissue burden and disease manifestations, they lack classical aspects of T-dependent responses, such as sustained IgG affinity maturation and longevity, corresponding with a rapid collapse of germinal centers. Instead, the Ab response is characterized by strong and ongoing secretion of IgM, whose origins and impact on protective immunity to B. burgdorferi remain unknown. In this article, we demonstrate that B. burgdorferi infection-induced IgM in mice was produced continuously, mainly by conventional B, not B-1 cells, in a T-independent manner. Although IgM was passively protective and restricted early bacteremia, its production had no effects on bacterial dissemination into solid tissues, nor did it affect Borrelia tissue burden. The latter was controlled by the induction of bactericidal IgG, as shown comparing infections in wild type mice with those of mice lacking exclusively secreted IgM-/-, all class-switched Abs via deletion of aicda (AID-/-), and all secreted Abs (secreted IgM-/- × AID-/-). Consistent with the notion that B. burgdorferi infection drives production of IgM over more tissue-penetrable IgG, we demonstrated increased short- and long-term IgM Ab responses also to a coadministered, unrelated Ag. Thus, the continued production of IgM may explain the absence of B. burgdorferi in the blood.

Antibody signatures in hospitalized hand, foot and mouth disease patients with acute enterovirus A71 infection

Enterovirus A71 (EV-A71) infection is a major cause of severe hand, foot and mouth disease (HFMD) in young children. The characteristics of EV-A71 neutralizing antibodies in HFMD patients are not well understood. In this study, we identified and cloned EV-A71-neutralizing antibodies by single cell RNA and B cell receptor sequencing of peripheral blood mononuclear cells. From 145 plasmablasts, we identified two IgG1 monoclonal antibodies (mAbs) and six IgM mAbs that neutralized EV-A71. Four of the IgM mAbs harbor germline variable sequences and neutralize EV-A71 potently. Two genetically similar IgM antibodies from two patients have recurrent heavy chain variable domain gene usage and similar complementarity-determining region 3 sequences. We mapped the residues of EV-A71 critical for neutralization through selection of virus variants resistant to antibody neutralization in the presence of neutralizing mAbs. The residues critical for neutralization are conserved among EV-A71 genotypes. Epitopes for the two genetically similar antibodies overlap with the SCARB2 binding site of EV-A71. We used escape variants to measure the epitope-specific antibody response in acute phase serum samples from EV-A71 infected HFMD patients. We found that these epitopes are immunogenic and contributed to the neutralizing antibody response against the virus. Our findings advance understanding of antibody response to EV-A71 infection in young children and have translational potential: the IgM mAbs could potentially be used for prevention or treatment of EV-A71 infections.

A Zika virus-specific IgM elicited in pregnancy exhibits ultrapotent neutralization

Congenital Zika virus (ZIKV) infection results in neurodevelopmental deficits in up to 14% of infants born to ZIKV-infected mothers. Neutralizing antibodies are a critical component of protective immunity. Here, we demonstrate that plasma IgM contributes to ZIKV immunity in pregnancy, mediating neutralization up to 3 months post-symptoms. From a ZIKV-infected pregnant woman, we isolated a pentameric ZIKV-specific IgM (DH1017.IgM) that exhibited ultrapotent ZIKV neutralization dependent on the IgM isotype. DH1017.IgM targets an envelope dimer epitope within domain II. The epitope arrangement on the virion is compatible with concurrent engagement of all ten antigen-binding sites of DH1017.IgM, a solution not available to IgG. DH1017.IgM protected mice against viremia upon lethal ZIKV challenge more efficiently than when expressed as an IgG. Our findings identify a role for antibodies of the IgM isotype in protection against ZIKV and posit DH1017.IgM as a safe and effective candidate immunotherapeutic, particularly during pregnancy.

B cells going viral in the CNS: Dynamics, complexities, and functions of B cells responding to viral encephalitis

A diverse number of DNA and RNA viruses have the potential to invade the central nervous system (CNS), causing inflammation and injury to cells that have a limited capacity for repair and regeneration. While rare, viral encephalitis in humans is often fatal and survivors commonly suffer from permanent neurological sequelae including seizures. Established treatment options are extremely limited, predominantly relying on vaccines, antivirals, or supportive care. Many viral CNS infections are characterized by the presence of antiviral antibodies in the cerebral spinal fluid (CSF), indicating local maintenance of protective antibody secreting cells. However, the mechanisms maintaining these humoral responses are poorly characterized. Furthermore, while both viral and autoimmune encephalitis are associated with the recruitment of diverse B cell subsets to the CNS, their protective and pathogenic roles aside from antibody production are just beginning to be understood. This review will focus on the relevance of B cell responses to viral CNS infections, with an emphasis on the importance of intrathecal immunity and the potential contribution to autoimmunity. Specifically, it will summarize the newest data characterizing B cell activation, differentiation, migration, and localization in clinical samples as well as experimental models of acute and persistent viral encephalitis.

West Nile virus in a patient with Good's syndrome

We describe the association between thymoma and hypogammaglobulinemia (Good's Syndrome) and a fulminant, seronegative West Nile Virus neuroinvasive infection confirmed by nucleic acid amplification. Diagnostic difficulties are emphasized and historical minutiae are highlighted.

Neuroinvasive West Nile Virus (WNV) Encephalitis With Anton Syndrome: Epidemiology and Pathophysiology Review

The West Nile virus (WNV) belongs to the genus of flaviviruses and is known to cause irreversible neurologic deficits. Neuroinvasive WNV cases continue to be rare and have a higher prevalence in South America, Africa, and Asia. Here we report a 55-year-old female from North America who presented with acute-onset encephalopathy, fever, myalgias, and Anton syndrome. Neuroradiographic findings included diffuse white matter abnormalities of both cortical and subcortical structures and the patient was diagnosed with posterior reversible encephalopathy syndrome (PRES). Further workup revealed WNV antibodies in both cerebrospinal fluid (CSF) and serum. Management of WNV encephalitis continues to be poor and thus the patient was referred to a long-term care facility. Furthermore, Anton syndrome is a rare focal neurologic deficit that has never been previously associated with the WNV. This case aims to highlight the epidemiology of WNV in the United States, the mechanisms of WNV encephalitis, and an overview of Anton syndrome. 

Immunogenicity of replication-deficient vesicular stomatitis virus based rabies vaccine in mice

BACKGROUND

Rabies is a viral disease that causes severe neurological manifestations both in humans and various mammals. Although inactivated and/or attenuated vaccines have been developed and widely used around the world, there are still concerns with regard to their safety, efficacy, and costs.

OBJECTIVE

As demand has grown for a new rabies vaccine, we have developed a new vesicular stomatitis viruses (VSVs) based rabies vaccine that replaces glycoproteins with rabies virus (RABV) glycoprotein (GP), or so-called VSV/RABV-GP.

METHODS

VSV/RABV-GP production was measured by sandwich ELISA. The generation of VSV/RABV-GP was evaluated with GP-specific antibodies and reduced transduction with GP-specific neutralizing antibodies. Virus entry was quantified by measuring the luciferase levels at 18-h post-transduction. BALB/c mice (three groups of six mice each) were intraperitoneally immunized with PBS, RABA, or VSV/RABV-GP at 0 and 14 days. At 28 days post-immunization serology was performed. Statistical significance was calculated using the Holm-Sidak multiple Student's t test.

RESULTS

Mice immunized with VSV/RABV-GP produced IgM and IgG antibodies, whereas IgM titers were significantly higher in mice immunized with VSV/RABV-GP compared to inactivated RABV. The secretion profiles of IgG1 and IgG2a production suggested that VSV/RAVB-GP induces the T helper cell type-2 immune bias. In addition, the average (±SD; n = 3) serum neutralization titers of the inactivated RABV and VSV/RABV-GP groups were 241 ± 40 and 103 ± 54 IU/mL, respectively.

CONCLUSION

Our results confirm that VSV/RABV-GP could be a new potential vaccination platform for RABV.

Single-cell transcriptome profiling and the use of AID deficient mice reveal that B cell activation combined with antibody class switch recombination and somatic hypermutation do not benefit the control of experimental trypanosomosis

Salivarian trypanosomes are extracellular protozoan parasites causing infections in a wide range of mammalian hosts, with Trypanosoma evansi having the widest geographic distribution, reaching territories far outside Africa and occasionally even Europe. Besides causing the animal diseases, T. evansi can cause atypical Human Trypanosomosis. The success of this parasite is attributed to its capacity to evade and disable the mammalian defense response. To unravel the latter, we applied here for the first time a scRNA-seq analysis on splenocytes from trypanosome infected mice, at two time points during infection, i.e. just after control of the first parasitemia peak (day 14) and a late chronic time point during infection (day 42). This analysis was combined with flow cytometry and ELISA, revealing that T. evansi induces prompt activation of splenic IgM+CD1d+ Marginal Zone and IgMIntIgD+ Follicular B cells, coinciding with an increase in plasma IgG2c Ab levels. Despite the absence of follicles, a rapid accumulation of Aicda+ GC-like B cells followed first parasitemia peak clearance, accompanied by the occurrence of Xbp1+ expressing CD138+ plasma B cells and Tbx21+ atypical CD11c+ memory B cells. Ablation of immature CD93+ bone marrow and Vpreb3+Ly6d+Ighm+ expressing transitional spleen B cells prevented mature peripheral B cell replenishment. Interestingly, AID-/- mice that lack the capacity to mount anti-parasite IgG responses, exhibited a superior defense level against T. evansi infections. Here, elevated natural IgMs were able to exert in vivo and in vitro trypanocidal activity. Hence, we conclude that in immune competent mice, trypanosomosis associated B cell activation and switched IgG production is rapidly induced by T. evansi, facilitating an escape from the detrimental natural IgM killing activity, and resulting in increased host susceptibility. This unique role of IgM and its anti-trypanosome activity are discussed in the context of the dilemma this causes for the future development of anti-trypanosome vaccines.

Obesity Enhances Disease Severity in Female Mice Following West Nile Virus Infection

A rise in adiposity in the United States has resulted in more than 70% of adults being overweight or obese, and global obesity rates have tripled since 1975. Following the 2009 H1N1 pandemic, obesity was characterized as a risk factor that could predict severe infection outcomes to viral infection. Amidst the SARS-CoV-2 pandemic, obesity has remained a significant risk factor for severe viral disease as obese patients have a higher likelihood for developing severe symptoms and requiring hospitalization. However, the mechanism by which obesity enhances viral disease is unknown. In this study, we utilized a diet-induced obesity mouse model of West Nile virus (WNV) infection, a flavivirus that cycles between birds and mosquitoes and incidentally infects both humans and mice. Likelihood for severe WNV disease is associated with risk factors such as diabetes that are comorbidities also linked to obesity. Utilizing this model, we showed that obesity-associated chronic inflammation increased viral disease severity as obese female mice displayed higher mortality rates and elevated viral titers in the central nervous system. In addition, our studies highlighted that obesity also dysregulates host acute adaptive immune responses, as obese female mice displayed significant dysfunction in neutralizing antibody function. These studies highlight that obesity-induced immunological dysfunction begins at early time points post infection and is sustained through memory phase, thus illuminating a potential for obesity to alter the differentiation landscape of adaptive immune cells.

Decreased antiviral immune response within the central nervous system of aged mice is associated with increased lethality of West Nile virus encephalitis

West Nile virus (WNV) is an emerging pathogen that causes disease syndromes ranging from a mild flu‐like illness to encephalitis. While the incidence of WNV infection is fairly uniform across age groups, the risk of lethal encephalitis increases with advanced age. Prior studies have demonstrated age‐related, functional immune deficits that limit systemic antiviral immunity and increase mortality; however, the effect of age on antiviral immune responses specifically within the central nervous system (CNS) is unknown. Here, we show that aged mice exhibit increased peripheral organ and CNS tissue viral burden, the latter of which is associated with alterations in activation of both myeloid and lymphoid cells compared with similarly infected younger animals. Aged mice exhibit lower MHCII expression by microglia, and higher levels of PD1 and lower levels of IFNγ expression by WNV‐specific CD8⁺ T cells in the CNS and CD8⁺CD45⁺ cells. These data indicate that the aged CNS exhibits limited local reactivation of T cells during viral encephalitis, which may lead to reduced virologic control at this site.

Immunopathogenesis of Different Emerging Viral Infections: Evasion, Fatal Mechanism, and Prevention

Different emerging viral infections may emerge in different regions of the world and pose a global pandemic threat with high fatality. Clarification of the immunopathogenesis of different emerging viral infections can provide a plan for the crisis management and prevention of emerging infections. This perspective article describes how an emerging viral infection evolves from microbial mutation, zoonotic and/or vector-borne transmission that progresses to a fatal infection due to overt viremia, tissue-specific cytotropic damage or/and immunopathology. We classified immunopathogenesis of common emerging viral infections into 4 categories: 1) deficient immunity with disseminated viremia (e.g., Ebola); 2) pneumocytotropism with/without later hyperinflammation (e.g., COVID-19); 3) augmented immunopathology (e.g., Hanta); and 4) antibody-dependent enhancement of infection with altered immunity (e.g., Dengue). A practical guide to early blocking of viral evasion, limiting viral load and identifying the fatal mechanism of an emerging viral infection is provided to prevent and reduce the transmission, and to do rapid diagnoses followed by the early treatment of virus neutralization for reduction of morbidity and mortality of an emerging viral infection such as COVID-19.

Novel Vaccine Technologies in Veterinary Medicine: A Herald to Human Medicine Vaccines

The success of inactivated and live-attenuated vaccines has enhanced livestock productivity, promoted food security, and attenuated the morbidity and mortality of several human, animal, and zoonotic diseases. However, these traditional vaccine technologies are not without fault. The efficacy of inactivated vaccines can be suboptimal with particular pathogens and safety concerns arise with live-attenuated vaccines. Additionally, the rate of emerging infectious diseases continues to increase and with that the need to quickly deploy new vaccines. Unfortunately, first generation vaccines are not conducive to such urgencies. Within the last three decades, veterinary medicine has spearheaded the advancement in novel vaccine development to circumvent several of the flaws associated with classical vaccines. These third generation vaccines, including DNA, RNA and recombinant viral-vector vaccines, induce both humoral and cellular immune response, are economically manufactured, safe to use, and can be utilized to differentiate infected from vaccinated animals. The present article offers a review of commercially available novel vaccine technologies currently utilized in companion animal, food animal, and wildlife disease control.

IgM and IgG Profiles Reveal Peculiar Features of Humoral Immunity Response to SARS-CoV-2 Infection

The emergence of coronavirus disease 2019 (COVID-19) is globally a major healthcare threat. There is little information regarding the mechanisms and roles of the humoral response in SARS-CoV-2 infection. The aim of this study was to analyze the antibody levels (IgM and IgG) by chemiluminescence immunoassay in 54 subjects positive to SARS-CoV-2 swab test in relation to their clinical status (whether asymptomatic, pauci-symptomatic or with mild, sever or critical symptoms), the time from the symptom onset, sex, age, and comorbidities. Overall, the presence of comorbidities and the age of subjects were associated with their clinical status. The IgG concentrations were significantly higher in patients who developed critical and severe symptoms and seemed to be independent from age, sex and comorbidities. IgG titers peaked around day 60, and then began gradually to drop, decreasing by approximately 50% on the 180th day, while the IgM titers progressively decreased as early as the tenth day, but they could be detected even at later time points. Despite the small number of individuals, some peculiar characteristics of the humoral response in COVID-19 emerged. We observed a high inter-individual variability, an ephemeral IgG half-life in several patients, and a persistence of IgM in others.

Acquisition and decay of IgM and IgG responses to merozoite antigens after Plasmodium falciparum malaria in Ghanaian children

Developing a vaccine against Plasmodium falciparum malaria has been challenging, primarily due to high levels of antigen polymorphism and a complex parasite lifecycle. Immunization with the P. falciparum merozoite antigens PfMSRP5, PfSERA9, PfRAMA, PfCyRPA and PfRH5 has been shown to give rise to growth inhibitory and synergistic antisera. Therefore, these five merozoite proteins are considered to be promising candidates for a second-generation multivalent malaria vaccine. Nevertheless, little is known about IgG and IgM responses to these antigens in populations that are naturally exposed to P. falciparum. In this study, serum samples from clinically immune adults and malaria exposed children from Ghana were studied to compare levels of IgG and IgM specific for PfMSRP5, PfSERA9, PfRAMA, PfCyRPA and PfRH5. All five antigens were found to be specifically recognized by both IgM and IgG in serum from clinically immune adults and from children with malaria. Longitudinal analysis of the latter group showed an early, transient IgM response that was followed by IgG, which peaked 14 days after the initial diagnosis. IgG levels and parasitemia did not correlate, whereas parasitemia was weakly positively correlated with IgM levels. These findings show that IgG and IgM specific for merozoite antigens PfMSRP5, PfSERA9, PfRAMA, PfCyRPA and PfRH5 are high in children during P. falciparum malaria, but that the IgM induction and decline occurs earlier in infection than that of IgG.

The Assessment of Convalescent Plasma Efficacy against COVID-19

Antibody-based therapy for infectious diseases predates modern antibiotics and, in the absence of other therapeutic options, was deployed early in the SARS-CoV-2 pandemic through COVID-19 convalescent plasma (CCP) administration. Although most studies have demonstrated signals of efficacy for CCP, definitive assessment has proved difficult under pandemic conditions, with rapid changes in disease incidence and the knowledge base complicating the design and implementation of randomized controlled trials. Nevertheless, evidence from a variety of studies demonstrates that CCP is as safe as ordinary plasma and strongly suggests that it can reduce mortality if given early and with sufficient antibody content.

What are protective antibody responses to pandemic SARS-CoV-2?

Human antibody responses to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) hold intense interest, with research efforts directed at optimizing antibody-based interventions and monitoring immune status. By relating individual variations in antibody response to coronavirus disease 2019 (COVID-19) severity, beneficial antiviral immune responses may be identified in detail. In this issue of the JCI, Secchi and collaborators describe antibody response profiles in 509 patients with COVID-19 from Italy during the 2020 pandemic. The research team found that multiple antibody types to multiple SARS-CoV-2 antigens developed over four weeks. Notably, IgG against the spike receptor binding domain (RBD) was predictive of survival and IgA against the viral spike protein (S protein) associated with rapid virologic clearance. These results may help guide selection of convalescent plasma, hyperimmune products, monoclonal antibodies, and vaccine strategies for COVID-19.

SARS-CoV-2 viral load and antibody responses: the case for convalescent plasma therapy

Most patients with COVID-19 lack antibody to SARS-CoV-2 in the first 10 days of illness while the virus drives disease pathogenesis. SARS-CoV-2 antibody deficiency in the setting of a tissue viral burden suggests that using an antibody as a therapeutic agent would augment the antiviral immune response. In this issue of the JCI, Wang and collaborators describe the kinetics of viral load and the antibody responses of 23 individuals with COVID-19 experiencing mild and severe disease. The researchers found that (a) individuals with mild and severe disease produced neutralizing IgG to SARS-CoV-2 10 days after disease onset, (b) SARS-CoV-2 persisted longer in those with severe disease, and (c) there was cross-reactivity between antibodies to SARS-CoV-1 and SARS-CoV-2, but only antibodies from patients with COVID-19 neutralized SARS-CoV-2. These observations provide important information on the serological response to SARS-CoV-2 of hospitalized patients with COVID-19 that can inform the use of convalescent plasma therapy.

MAVS regulates the quality of the antibody response to West-Nile Virus

A key difference that distinguishes viral infections from protein immunizations is the recognition of viral nucleic acids by cytosolic pattern recognition receptors (PRRs). Insights into the functions of cytosolic PRRs such as the RNA-sensing Rig-I-like receptors (RLRs) in the instruction of adaptive immunity are therefore critical to understand protective immunity to infections. West Nile virus (WNV) infection of mice deficent of RLR-signaling adaptor MAVS results in a defective adaptive immune response. While this finding suggests a role for RLRs in the instruction of adaptive immunity to WNV, it is difficult to interpret due to the high WNV viremia, associated exessive antigen loads, and pathology in the absence of a MAVS-dependent innate immune response. To overcome these limitations, we have infected MAVS-deficient (MAVSKO) mice with a single-round-of-infection mutant of West Nile virus. We show that MAVSKO mice failed to produce an effective neutralizing antibody response to WNV despite normal antibody titers against the viral WNV-E protein. This defect occurred independently of antigen loads or overt pathology. The specificity of the antibody response in infected MAVSKO mice remained unchanged and was still dominated by antibodies that bound the neutralizing lateral ridge (LR) epitope in the DIII domain of WNV-E. Instead, MAVSKO mice produced IgM antibodies, the dominant isotype controlling primary WNV infection, with lower affinity for the DIII domain. Our findings suggest that RLR-dependent signals are important for the quality of the humoral immune response to WNV.

Acute RNA Viral Encephalomyelitis and the Role of Antibodies in the Central Nervous System

Acute RNA viral encephalomyelitis is a serious complication of numerous virus infections. Antibodies in the cerebral spinal fluid (CSF) are correlated to better outcomes, and there is substantive evidence of antibody secreting cells (ASCs) entering the central nervous system (CNS) and contributing to resolution of infection. Here, we review the RNA viruses known to cause acute viral encephalomyelitis with mechanisms of control that require antibody or ASCs. We compile the cytokines, chemokines, and surface receptors associated with ASC recruitment to the CNS after infection and compare known antibody-mediated mechanisms as well as potential noncytolytic mechanisms for virus control. These non-canonical functions of antibodies may be employed in the CNS to protect precious non-renewable neurons. Understanding the immune-specialized zone of the CNS is essential for the development of effective treatments for acute encephalomyelitis caused by RNA viruses.

Immunoglobulin M: An Ancient Antiviral Weapon - Rediscovered

Recent discoveries have shed new light onto immunoglobulin M (IgM), an ancient antibody class preserved throughout evolution in all vertebrates. First, IgM – long thought to be a perfect pentamer – was shown to be asymmetric, resembling a quasi-hexamer missing one monomer and containing a gap. Second, this gap allows IgM to serve as carrier of a specific host protein, apoptosis inhibitor of macrophages (AIM), which is released to promote removal of dead-cell debris, cancer cells, or pathogens. Third, recombinant IgM delivered mucosally by passive immunization gave proof-of-concept that this antibody class can prevent mucosal simian-human immunodeficiency virus transmission in non-human primates. Finally, IgM’s role in adaptive immunity goes beyond being only a first defender to respond to pathogen invasion, as long-lived IgM plasma cells have been observed predominantly residing in the spleen. In fact, IgM produced by such cells contained somatic hypermutations and was linked to protection against lethal influenza virus challenge in murine models. Importantly, such long-lived IgM plasma cells had been induced by immunization 1 year before challenge. Together, new data on IgM function raise the possibility that vaccine strategies aimed at preventing virus acquisition could include this ancient weapon.

Basic insights into Zika virus infection of neuroglial and brain endothelial cells

Zika virus (ZIKV) has recently emerged as an important human pathogen due to the strong evidence that it causes disease of the central nervous system, particularly microcephaly and Guillain-Barré syndrome. The pathogenesis of disease, including mechanisms of neuroinvasion, may include both invasion via the blood-brain barrier and via peripheral (including cranial) nerves. Cellular responses to infection are also poorly understood. This study characterizes the in vitro infection of laboratory-adapted ZIKV African MR766 and two Asian strains of (1) brain endothelial cells (hCMEC/D3 cell line) and (2) olfactory ensheathing cells (OECs) (the neuroglia populating cranial nerve I and the olfactory bulb; both human and mouse OEC lines) in comparison to kidney epithelial cells (Vero cells, in which ZIKV infection is well characterized). Readouts included infection kinetics, intracellular virus localization, viral persistence and cytokine responses. Although not as high as in Vero cells, viral titres exceeded 104 plaque-forming units (p.f.u.) ml-1 in the endothelial/neuroglial cell types, except hOECs. Despite these substantial titres, a relatively small proportion of neuroglial cells were primarily infected. Immunolabelling of infected cells revealed localization of the ZIKV envelope and NS3 proteins in the cytoplasm; NS3 staining overlapped with that of dsRNA replication intermediate and the endoplasmic reticulum (ER). Infected OECs and endothelial cells produced high levels of pro-inflammatory chemokines. Nevertheless, ZIKV was also able to establish persistent infection in hOEC and hCMEC/D3 cells. Taken together, these results provide basic insights into ZIKV infection of endothelial and neuroglial cells and will form the basis for further study of ZIKV disease mechanisms.

West Nile Virus Restriction in Mosquito and Human Cells: A Virus under Confinement

West Nile virus (WNV) is an emerging neurotropic flavivirus that naturally circulates between mosquitoes and birds. However, WNV has a broad host range and can be transmitted from mosquitoes to several mammalian species, including humans, through infected saliva during a blood meal. Although WNV infections are mostly asymptomatic, 20% to 30% of cases are symptomatic and can occasionally lead to severe symptoms, including fatal meningitis or encephalitis. Over the past decades, WNV-carrying mosquitoes have become increasingly widespread across new regions, including North America and Europe, which constitutes a public health concern. Nevertheless, mosquito and human innate immune defenses can detect WNV infection and induce the expression of antiviral effectors, so-called viral restriction factors, to control viral propagation. Conversely, WNV has developed countermeasures to escape these host defenses, thus establishing a constant arms race between the virus and its hosts. Our review intends to cover most of the current knowledge on viral restriction factors as well as WNV evasion strategies in mosquito and human cells in order to bring an updated overview on WNV-host interactions.

Dynamics of IgM and IgG responses to the next generation of engineered Duffy binding protein II immunogen: Strain-specific and strain-transcending immune responses over a nine-year period

BACKGROUND

A low proportion of P. vivax-exposed individuals acquire protective strain-transcending neutralizing IgG antibodies that are able to block the interaction between the Duffy binding protein II (DBPII) and its erythrocyte-specific invasion receptor. In a recent study, a novel surface-engineered DBPII-based vaccine termed DEKnull-2, whose antibody response target conserved DBPII epitopes, was able to induce broadly binding-inhibitory IgG antibodies (BIAbs) that inhibit P. vivax reticulocyte invasion. Toward the development of DEKnull-2 as an effective P. vivax blood-stage vaccine, we investigate the relationship between naturally acquired DBPII-specific IgM response and the profile of IgG antibodies/BIAbs activity over time.

METHODOLOGY/PRINCIPAL FINDINGS

A nine-year follow-up study was carried-out among long-term P. vivax-exposed Amazonian individuals and included six cross-sectional surveys at periods of high and low malaria transmission. DBPII immune responses associated with either strain-specific (Sal1, natural DBPII variant circulating in the study area) or conserved epitopes (DEKnull-2) were monitored by conventional serology (ELISA-detected IgM and IgG antibodies), with IgG BIAbs activity evaluated by functional assays (in vitro inhibition of DBPII-erythrocyte binding). The results showed a tendency of IgM antibodies toward Sal1-specific response; the profile of Sal1 over DEKnull-2 was not associated with acute malaria and sustained throughout the observation period. The low malaria incidence in two consecutive years allowed us to demonstrate that variant-specific IgG (but not IgM) antibodies waned over time, which resulted in IgG skewed to the DEKnull-2 response. A persistent DBPII-specific IgM response was not associated with the presence (or absence) of broadly neutralizing IgG antibody response.

CONCLUSIONS/SIGNIFICANCE

The current study demonstrates that long-term exposure to low and unstable levels of P. vivax transmission led to a sustained DBPII-specific IgM response against variant-specific epitopes, while sustained IgG responses are skewed to conserved epitopes. Further studies should investigate on the role of a stable and persistent IgM antibody response in the immune response mediated by DBPII.

Drivers and regulators of humoral innate immune responses to infection and cancer

The complement cascade consists of cell bound and serum proteins acting together to protect the host from pathogens, remove cancerous cells and effectively links innate and adaptive immune responses. Despite its usefulness in microbial neutralization and clearance of cancerous cells, excessive complement activation causes an immune imbalance and tissue damage in the host. Hence, a series of complement regulatory proteins present at a higher concentration in blood plasma and on cell surfaces tightly regulate the cascade. The complement cascade can be initiated by B-1 B cell production of natural antibodies. Natural antibodies arise spontaneously without any known exogenous antigenic or microbial stimulus and protect against invading pathogens, clear apoptotic cells, provide tissue homeostasis, and modulate adaptive immune functions. Natural IgM antibodies recognize microbial and cancer antigens and serve as an activator of complement mediated lysis. This review will discuss advances in complement activation and regulation in bacterial and viral infections, and cancer. We will also explore the crosstalk of natural antibodies with bacterial populations and cancer.

Not all therapeutic antibody isotypes are equal: the case of IgM versus IgG in Pertuzumab and Trastuzumab

The therapeutic potential of immunoglobulin M (IgM) is of considerable interest in immunotherapy due to its complement-activating and cell-agglutinating abilities. Pertuzumab and Trastuzumab are monoclonal antibodies used to treat human epidermal growth factor receptor 2 (HER2)-positive breast cancer but exhibit significantly different binding affinities as IgM when compared to its IgG isotype. Using integrative multiscale modelling and simulations of complete antibody assemblies, we show that Pertuzumab IgM is able to utilize all of its V-regions to bind multiple HER2 receptors simultaneously, while similar binding in Trastuzumab IgM is prohibited by steric clashes caused by the large globular domain of HER2. This is subsequently validated by confirming that Pertuzumab IgM inhibits proliferation in HER2 over-expressing live cells more effectively than its IgG counterpart and Trastuzumab IgM. Our study highlights the importance of understanding the molecular details of antibody-antigen interactions for the design and isotype selection of therapeutic antibodies.

Impact of flavivirus vaccine-induced immunity on primary Zika virus antibody response in humans

Background

Zika virus has recently spread to South- and Central America, causing congenital birth defects and neurological complications. Many people at risk are flavivirus pre-immune due to prior infections with other flaviviruses (e.g. dengue virus) or flavivirus vaccinations. Since pre-existing cross-reactive immunity can potentially modulate antibody responses to Zika virus infection and may affect the outcome of disease, we analyzed fine-specificity as well as virus-neutralizing and infection-enhancing activities of antibodies induced by a primary Zika virus infection in flavivirus-naïve as well as yellow fever- and/or tick-borne encephalitis-vaccinated individuals.

Methodology

Antibodies in sera from convalescent Zika patients with and without vaccine-induced immunity were assessed by ELISA with respect to Zika virus-specificity and flavivirus cross-reactivity. Functional analyses included virus neutralization and infection-enhancement. The contribution of IgM and cross-reactive antibodies to these properties was determined by depletion experiments.

Principal findings

Pre-existing flavivirus immunity had a strong influence on the antibody response in primary Zika virus infections, resulting in higher titers of broadly flavivirus cross-reactive antibodies and slightly lower levels of Zika virus-specific IgM. Antibody-dependent enhancement (ADE) of Zika virus was mediated by sub-neutralizing concentrations of specific IgG but not by cross-reactive antibodies. This effect was potently counteracted by the presence of neutralizing IgM. Broadly cross-reactive antibodies were able to both neutralize and enhance infection of dengue virus but not Zika virus, indicating a different exposure of conserved sequence elements in the two viruses.

Conclusions

Our data point to an important role of flavivirus-specific IgM during the transient early stages of infection, by contributing substantially to neutralization and by counteracting ADE. In addition, our results highlight structural differences between strains of Zika and dengue viruses that are used for analyzing infection-enhancement by cross-reactive antibodies. These findings underscore the possible impact of specific antibody patterns on flavivirus disease and vaccination efficacy.

The explosive spread of Zika virus, a flavivirus, to South- and Central America underscores the potential threat of newly emerging arthropod-borne viruses. Zika virus infection can cause congenital birth defects and neurological complications. Many people at risk are flavivirus pre-immune because of prior infections with other flaviviruses (e.g. dengue virus, which co-circulates in Zika outbreak regions) or vaccinations (e.g. against yellow fever or tick-borne encephalitis) and have non-protective cross-reactive antibodies at the time of infection. Since pre-existing immunity can modulate the specificity and functional activity of antibody responses, and cross-reactive antibodies have been implicated in disease enhancement, we compared the specificities of serum samples from flavivirus-naïve and vaccinated individuals after primary Zika virus infections. Prior immunity led to a strong booster of cross-reactive antibodies that did not neutralize Zika virus. Importantly, we could also show that newly formed IgM antibodies contributed significantly to virus neutralization and prevented infection enhancement by other antibodies. Our data thus show how pre-existing cross-reactive immunities can alter the specificities and functional activities of antibody responses in flavivirus infections, which may affect flavivirus-induced disease and the efficacy of vaccinations.

West Nile or Usutu Virus? A Three-Year Follow-Up of Humoral and Cellular Response in a Group of Asymptomatic Blood Donors

West Nile virus (WNV) and Usutu virus (USUV) are two related arboviruses (genus Flavivirus, family Flaviviridae), with birds as a reservoir and mosquitoes as transmitting vectors. In recent years, WNV epidemiology changed in many European countries with increased frequency of outbreaks posing the issue of virus transmission risks by blood transfusion. USUV emerged for the first time in birds of the Tuscany region (Italy) in 1996 and in 2001 in Austria. While WNV is responsible for both mild and neuroinvasive diseases, USUV infection is usually asymptomatic and neuroinvasive symptoms are rare. Since WNV and USUV co-circulate, the surveillance of WNV allows also the detection of USUV. Due to the great similarity in amino-acid sequence of major surface proteins of the two viruses, a high cross-reactivity can lead to misinterpretation of serological results. Here, we report the results obtained from 54 asymptomatic blood donors during a three-year follow-up showing an unexpected high positivity (46.3%) for USUV. The major obstacle encountered in the differential diagnosis between these two viruses was the high cross-reactivity found in neutralizing antibodies (NT Abs) and, in some cases, a long follow-up was mandatory for a correct diagnosis. Moreover, two new ELISpot assays were developed for a more rapid and specific differential diagnosis, especially in those cases in which NT Abs were not determinant. Using a combination of Enzyme-linked immunospot (ELISpot), molecular, and serological tests, we could identify 25 true positive WNV and 25 true positive USUV blood donors. Our data highlight the importance of raising awareness for increasing USUV infections in endemic countries involved in blood transfusion and organ donation.

Immune Correlates of Protection From West Nile Virus Neuroinvasion and Disease

BACKGROUND

A challenge to the design of improved therapeutic agents and prevention strategies for neuroinvasive infection and associated disease is the lack of known natural immune correlates of protection. A relevant model to study such correlates is offered by the Collaborative Cross (CC), a panel of recombinant inbred mouse strains that exhibit a range of disease manifestations upon infection.

METHODS

We performed an extensive screen of CC-F1 lines infected with West Nile virus (WNV), including comprehensive immunophenotyping, to identify groups of lines that exhibited viral neuroinvasion or neuroinvasion with disease and lines that remained free of WNV neuroinvasion and disease.

RESULTS

Our data reveal that protection from neuroinvasion and disease is multifactorial and that several immune outcomes can contribute. Immune correlates identified include decreased suppressive activity of regulatory T cells at steady state, which correlates with peripheral restriction of the virus. Further, a rapid contraction of WNV-specific CD8+ T cells in the brain correlated with protection from disease.

CONCLUSIONS

These immune correlates of protection illustrate additional networks and pathways of the WNV immune response that cannot be observed in the C57BL/6 mouse model. Additionally, correlates of protection exhibited before infection, at baseline, provide insight into phenotypic differences in the human population that may predict clinical outcomes upon infection.

Envelope-Specific IgG3 and IgG1 Responses Are Associated with Clearance of Acute Hepatitis C Virus Infection

Hepatitis C virus (HCV) can be cleared naturally in a subset of individuals. However, the asymptomatic nature of acute HCV infection makes the study of the early immune response and defining the correlates of protection challenging. Despite this, there is now strong evidence implicating the humoral immune response, specifically neutralising antibodies, in determining the clearance or chronicity outcomes of primary HCV infection. In general, immunoglobulin G (IgG) plays the major role in viral neutralisation. However, there are limited investigations of anti-HCV envelope protein 2 (E2) isotypes (IgM, IgG, IgA) and IgG subclasses (IgG1-4) in early HCV infection. In this study, using a rare cohort of 14 very recently HCV-infected individuals (4-45 days) with varying disease outcome (n = 7 clearers), the timing and potency of anti-HCV E2 isotypes and IgG subclasses were examined longitudinally, in relation to neutralising antibody activity. Clearance was associated with anti-E2 IgG, specifically IgG1 and IgG3, and appeared essential to prevent the emergence of new HCV variants and the chronic infection outcome. Interestingly, these IgG responses were accompanied by IgM antibodies and were associated with neutralising antibody activity in the subjects who cleared infection. These findings provide novel insights into the early humoral immune response characteristics associated with HCV disease outcome.

Oral Antibiotic Treatment of Mice Exacerbates the Disease Severity of Multiple Flavivirus Infections

Although the outcome of flavivirus infection can vary from asymptomatic to lethal, environmental factors modulating disease severity are poorly defined. Here, we observed increased susceptibility of mice to severe West Nile (WNV), Dengue, and Zika virus infections after treatment with oral antibiotics (Abx) that depleted the gut microbiota. Abx treatment impaired the development of optimal T cell responses, with decreased levels of WNV-specific CD8⁺ T cells associated with increased infection and immunopathology. Abx treatments that resulted in enhanced WNV susceptibility generated changes in the overall structure of the gut bacterial community and in the abundance of specific bacterial taxa. As little as 3 days of treatment with ampicillin was sufficient to alter host immunity and WNV outcome. Our results identify oral Abx therapy as a potential environmental determinant of systemic viral disease, and they raise the possibility that perturbation of the gut microbiota may have deleterious consequences for subsequent flavivirus infections.

Current Understanding of West Nile Virus Clinical Manifestations, Immune Responses, Neuroinvasion, and Immunotherapeutic Implications

West Nile virus (WNV) is the most common mosquito-borne virus in North America. WNV-associated neuroinvasive disease affects all ages, although elderly and immunocompromised individuals are particularly at risk. WNV neuroinvasive disease has killed over 2300 Americans since WNV entered into the United States in the New York City outbreak of 1999. Despite 20 years of intensive laboratory and clinical research, there are still no approved vaccines or antivirals available for human use. However, rapid progress has been made in both understanding the pathogenesis of WNV and treatment in clinical practices. This review summarizes our current understanding of WNV infection in terms of human clinical manifestations, host immune responses, neuroinvasion, and therapeutic interventions.

The immunity features and defects against primary cytomegalovirus infection post-splenectomy indicate an immunocompromised status: A PRISMA-compliant meta-analysis

BACKGROUND

To evaluate if splenectomy results in severely impaired immune responses against primary cytomegalovirus (CMV) infection compared to the general immunocompetent population.

METHODS

We performed a systemic literature review to study CMV infections in splenectomized individuals, a special population group presently considered immunocompetent to viral infections. We retrieved 30 cases with established CMV infection post-splenectomy and we recorded their disease manifestations, laboratory findings, immunological studies, and histopathology reports. In addition, we retrieved numerous multidisciplinary articles in view of post-splenectomy immunology defects, as well as of immune responses to primary invading CMV in the absence of the spleen. Two clinical studies directly comparing splenectomized with nonsplenectomized individuals under severe iatrogenic immunosuppression as well as the numerically largest review articles of CMV infections in immunocompetent were retained.

RESULTS

Splenectomy results in the loss of spleen's ability to fend-off blood-borne pathogens and impairs the link between innate and adaptive immunity. The major post-splenectomy immune-defects against CMV are: weakened, delayed or absent anti-CMV IgM, and compensatory marked IgG response; severely impaired B-cell and CD4, CD8 T-cells function responses; and post-splenectomy, bone marrow compensates for the absence of spleen's immune responses against CMV, mimicking a monoclonal T-cell lymphoproliferative process.

CONCLUSION

The puzzled diagnosis of the CMV syndrome post-splenectomy is of the most challenging and misleading, resulting in risky and costly interventions and a subsequent prolonged hospitalization (2 months). The mounting multi-disciplinary literature evidence renders us to suggest that splenectomized individuals are not only prone to encapsulated bacteria but also behave as immunocompromised to CMV.

Dendritic cell-associated MAVS is required to control West Nile virus replication and ensuing humoral immune responses

Mitochondrial antiviral signaling protein (MAVS) is a critical innate immune signaling protein that directs the actions of the RIG-I-like receptor (RLR) signaling pathway of RNA virus recognition and initiation of anti-viral immunity against West Nile virus (WNV). In the absence of MAVS, mice die more rapidly after infection with the pathogenic WNV-Texas (TX) strain, but also produce elevated WNV-specific IgG concomitant with increased viral burden. Here we investigated whether there was a B cell intrinsic role for MAVS during the development of protective humoral immunity following WNV infection. MAVS-/- mice survived infection from the non-pathogenic WNV-Madagascar (MAD) strain, with limited signs of disease. Compared to wildtype (WT) controls, WNV-MAD-infected MAVS-/- mice had elevated serum neutralizing antibodies, splenic germinal center B cells, plasma cells and effector T cells. We found that when rechallenged with the normally lethal WNV-TX, MAVS-/- mice previously infected with WNV-MAD were protected from disease. Thus, protective humoral and cellular immune responses can be generated in absence of MAVS. Mice with a conditional deletion of MAVS only in CD11c+ dendritic cells phenocopied MAVS whole body knockout mice in their humoral responses to WNV-MAD, displaying elevated virus titers and neutralizing antibodies. Conversely, a B cell-specific deletion of MAVS had no effect on immune responses to WNV-MAD compared to WT controls. Thus, MAVS in dendritic cells is required to control WNV replication and thereby regulate downstream humoral immune responses.

Antiviral Functions of Monoclonal Antibodies against Chikungunya Virus

Chikungunya virus (CHIKV) is the most common alphavirus infecting humans worldwide. Antibodies play pivotal roles in the immune response to infection. Increasingly, therapeutic antibodies are becoming important for protection from pathogen infection for which neither vaccine nor treatment is available, such as CHIKV infection. The new generation of ultra-potent and/or broadly cross-reactive monoclonal antibodies (mAbs) provides new opportunities for intervention. In the past decade, several potent human and mouse anti-CHIKV mAbs were isolated and demonstrated to be protective in vivo. Mechanistic studies of these mAbs suggest that mAbs exert multiple modes of action cooperatively. Better understanding of these antiviral mechanisms for mAbs will help to optimize mAb therapies.

Basics of memory B-cell responses: lessons from and for the real world

The production of pathogen-specific B cells and antibodies underlies protective immunity elicited by most vaccines and many infections. Humoral immunity follows a regulated process by which high-affinity antibody-secreting plasma cells and memory B cells are generated. Yet for certain pathogens, protective immunity is inefficiently generated and/or maintained. For example, Dengue virus infections lead to lasting immunity against re-infection by the same serotype. However, if infected with a different Dengue serotype, the individual is predisposed to more severe disease than if he/she was completely naive. As another example, both natural infections with or vaccination against malaria do not necessarily lead to lasting immunity, as the same individual can be re-infected many times over the course of a lifetime. In this review, we discuss how these real-world problems can both instruct and be informed by recent basic studies using model organisms and antigens. An emphasis is placed on protective epitopes and functional distinctions between memory B-cell subsets in both mice and humans. Using flavivirus and Plasmodium infections as examples, we also speculate on the differences between ineffective B-cell responses that actually occur in the real world, and perfect-world responses that would generate lasting immunity.

T Lymphocytes as Measurable Targets of Protection and Vaccination Against Viral Disorders

Continuous epidemiological surveillance of existing and emerging viruses and their associated disorders is gaining importance in light of their abilities to cause unpredictable outbreaks as a result of increased travel and vaccination choices by steadily growing and aging populations. Close surveillance of outbreaks and herd immunity are also at the forefront, even in industrialized countries, where previously eradicated viruses are now at risk of re-emergence due to instances of strain recombination, contractions in viral vector geographies, and from their potential use as agents of bioterrorism. There is a great need for the rational design of current and future vaccines targeting viruses, with a strong focus on vaccine targeting of adaptive immune effector memory T cells as the gold standard of immunity conferring long-lived protection against a wide variety of pathogens and malignancies. Here, we review viruses that have historically caused large outbreaks and severe lethal disorders, including respiratory, gastric, skin, hepatic, neurologic, and hemorrhagic fevers. To observe trends in vaccinology against these viral disorders, we describe viral genetic, replication, transmission, and tropism, host-immune evasion strategies, and the epidemiology and health risks of their associated syndromes. We focus on immunity generated against both natural infection and vaccination, where a steady shift in conferred vaccination immunogenicity is observed from quantifying activated and proliferating, long-lived effector memory T cell subsets, as the prominent biomarkers of long-term immunity against viruses and their associated disorders causing high morbidity and mortality rates.

The conduit system exports locally secreted IgM from lymph nodes

IgM provides early protection against pathogens. How IgM is exported out of lymph nodes remains unknown. Thierry et al. report that B cells utilize a system of paracortical conduits to rapidly export their IgM to the periphery.

Immunoglobulin M (IgM) is the first type of antibody produced during acute infections and thus provides an early line of specific defense against pathogens. Being produced in secondary lymphoid organs, IgM must rapidly be exported to the blood circulation. However, it is currently unknown how such large pentameric molecules are released from lymph nodes (LNs). Here, we show that upon immunization, IgM transiently gains access to the luminal side of the conduit system, a reticular infrastructure enabling fast delivery of tissue-derived soluble substances to the LN parenchyma. Using microinjections of purified IgM, we demonstrate that conduit-associated IgM is delivered by neither the afferent lymph nor the blood, but is locally conveyed by conduits. Exploiting in vivo models, we further demonstrate that conduit-associated IgM is locally and transiently produced by activated, antigen-specific B cells migrating in the T cell zone. Thus, our study reveals that the conduit system is coopted by B cells to rapidly export secreted IgM out of LNs.

Active Human Complement Reduces the Zika Virus Load via Formation of the Membrane-Attack Complex

Although neglected in the past, the interest on Zika virus (ZIKV) raised dramatically in the last several years. The rapid spread of the virus in Latin America and the association of the infection with microcephaly in newborns or Guillain-Barré Syndrome in adults prompted the WHO to declare the ZIKV epidemic to be an international public health emergency in 2016. As the virus gained only limited attention in the past, investigations on interactions of ZIKV with human complement are limited. This prompted us to investigate the stability of the virus to human complement. At low serum concentrations (10%) which refers to complement concentrations found on mucosal surfaces, the virus was relatively stable at 37°C, while at high complement levels (50% serum concentration) ZIKV titers were dramatically reduced, although the virus remained infectious for about 4–5 min under these conditions. The classical pathway was identified as the main actor of complement activation driven by IgM antibodies. In addition, direct binding of C1q to both envelope and NS1 proteins was observed. Formation of the MAC on the viral surface and thus complement-mediated lysis and not opsonization seems to be essential for the reduction of viral titers.

Critical role of CD4+ T cells and IFNγ signaling in antibody-mediated resistance to Zika virus infection

Protective adaptive immunity to Zika virus (ZIKV) has been mainly attributed to cytotoxic CD8⁺ T cells and neutralizing antibodies, while the participation of CD4⁺ T cells in resistance has remained largely uncharacterized. Here, we show a neutralizing antibody response, dependent on CD4⁺ T cells and IFNγ signaling, which we detected during the first week of infection and is associated with reduced viral load in the brain, prevention of rapid disease onset and survival. We demonstrate participation of these components in the resistance to ZIKV during primary infection and in murine adoptive transfer models of heterologous ZIKV infection in a background of IFNR deficiency. The protective effect of adoptively transferred CD4⁺ T cells requires IFNγ signaling, CD8⁺ T cells and B lymphocytes in recipient mice. Together, this indicates the importance of CD4⁺ T cell responses in future vaccine design for ZIKV.

Intrathecal expression of IL-5 and humoral response in patients with tick-borne encephalitis

AIM

The aim of the study was to assess the role of an early specific humoral response in human infection with a tick-borne encephalitis virus (TBEV) and the role of IL-5 as its potential mediator and marker.

MATERIALS AND METHODS

The retrospective study involved a cohort of 199 patients diagnosed with TBE, in whom anti-TBEV IgM and IgG antibody titers were analyzed on admission and compared with clinical presentation and basic laboratory parameters. The prospective study included 50 TBE patients in whom IL-5 serum and CSF concentration was measured with ELISA on admission in the TBE neurologic phase and in selected patients before discharge, at follow-up or in samples obtained before the neurologic phase onset.

RESULTS

The serum anti-TBEV IgM correlated with good clinical outcome and the CSF anti-TBEV IgM with more pronounced CSF inflammation on admission, but also with its more complete resolution on follow-up. The serum anti-TBEV IgG correlated with milder presentation and better outcome. Concentration of IL-5 was increased in CSF but not in the serum of TBE patients. IL-5 concentration index on admission favored its intrathecal synthesis. IL-5 did not correlate significantly with clinical presentation and specific IgM and IgG titers.

CONCLUSIONS

Specific anti-TBEV IgM systemic and intrathecal response and IgG systemic response are protective, together favoring milder presentation, better outcome and resolution of central nervous system (CNS) inflammation. IL-5 is expressed intrathecally in TBE, but its pathogenetic role remains unclear.

Germ Line IgM Is Sufficient, but Not Required, for Antibody-Mediated Alphavirus Clearance from the Central Nervous System

Sindbis virus (SINV) infection of neurons in the brain and spinal cord in mice provides a model system for investigating recovery from encephalomyelitis and antibody-mediated clearance of virus from the central nervous system (CNS). To determine the roles of IgM and IgG in recovery, we compared the responses of immunoglobulin-deficient activation-induced adenosine deaminase-deficient (AID^-/-), secretory IgM-deficient (sIgM^-/-), and AID^-/- sIgM^-/- double-knockout (DKO) mice with those of wild-type (WT) C57BL/6 mice for disease, clearance of infectious virus and viral RNA from brain and spinal cord, antibody responses, and B cell infiltration into the CNS. Because AID is essential for immunoglobulin class switch recombination and somatic hypermutation, AID^-/- mice produce only germ line IgM, while sIgM^-/- mice secrete IgG but no IgM and DKO mice produce no secreted immunoglobulin. After intracerebral infection with the TE strain of SINV, most mice recovered. Development of neurologic disease occurred slightly later in sIgM^-/- mice, but disease severity, weight loss, and survival were similar between the groups. AID^-/- mice produced high levels of SINV-specific IgM, while sIgM^-/- mice produced no IgM and high levels of IgG2a compared to WT mice. All mice cleared infectious virus from the spinal cord, but DKO mice failed to clear infectious virus from brain and had higher levels of viral RNA in the CNS late after infection. The numbers of infected cells and the amount of cell death in brain were comparable. We conclude that antibody is required and that either germ line IgM or IgG is sufficient for clearance of virus from the CNS.IMPORTANCE Mosquito-borne alphaviruses that infect neurons can cause fatal encephalomyelitis. Recovery requires a mechanism for the immune system to clear virus from infected neurons without harming the infected cells. Antiviral antibody has previously been shown to be a noncytolytic means for alphavirus clearance. Antibody-secreting cells enter the nervous system after infection and produce antiviral IgM before IgG. Clinical studies of human viral encephalomyelitis suggest that prompt production of IgM is associated with recovery, but it was not known whether IgM is effective for clearance. Our studies used mice deficient in production of IgM, IgG, or both to characterize the antibody necessary for alphavirus clearance. All mice developed similar signs of neurologic disease and recovered from infection. Antibody was necessary for virus clearance from the brain, and either early germ line IgM or IgG was sufficient. These studies support the clinical observation that prompt production of antiviral antibody is a determinant of outcome.

Splenic macrophages are required for protective innate immunity against West Nile virus

Although the spleen is a major site for West Nile virus (WNV) replication and spread, relatively little is known about which innate cells in the spleen replicate WNV, control viral dissemination, and/or prime innate and adaptive immune responses. Here we tested if splenic macrophages (MΦs) were necessary for control of WNV infection. We selectively depleted splenic MΦs, but not draining lymph node MΦs, by injecting mice intravenously with clodronate liposomes several days prior to infecting them with WNV. Mice missing splenic MΦs succumbed to WNV infection after an increased and accelerated spread of virus to the spleen and the brain. WNV-specific Ab and CTL responses were normal in splenic MΦ-depleted mice; however, numbers of NK cells and CD4 and CD8 T cells were significantly increased in the brains of infected mice. Splenic MΦ deficiency led to increased WNV in other splenic innate immune cells including CD11b- DCs, newly formed MΦs and monocytes. Unlike other splenic myeloid subsets, splenic MΦs express high levels of mRNAs encoding the complement protein C1q, the apoptotic cell clearance protein Mertk, the IL-18 cytokine and the FcγR1 receptor. Splenic MΦ-deficient mice may be highly susceptible to WNV infection in part to a deficiency in C1q, Mertk, IL-18 or Caspase 12 expression.

An Overview of Current Approaches Toward the Treatment and Prevention of West Nile Virus Infection

The persistence of West Nile virus (WNV) infections throughout the USA since its inception in 1999 and its continuous spread throughout the globe calls for an urgent need of effective treatments and prevention measures. Although the licensing of several WNV vaccines for veterinary use provides a proof of concept, similar efforts on the development of an effective vaccine for humans remain still unsuccessful. Increased understanding of biology and pathogenesis of WNV together with recent technological advancements have raised hope that an effective WNV vaccine may be available in the near future. In addition, rapid progress in the structural and functional characterization of WNV and other flaviviral proteins have provided a solid base for the design and development of several classes of inhibitors as potential WNV therapeutics. Moreover, the therapeutic monoclonal antibodies demonstrate an excellent efficacy against WNV in animal models and represent a promising class of WNV therapeutics. However, there are some challenges as to the design and development of a safe and efficient WNV vaccine or therapeutic. In this chapter, we discuss the current approaches, progress, and challenges toward the development of WNV vaccines, therapeutic antibodies, and antiviral drugs.