Predicting Vibrio cholerae infection and symptomatic disease: a systems serology study

BACKGROUND

Vibriocidal antibodies are currently the best characterised correlate of protection against cholera and are used to gauge immunogenicity in vaccine trials. Although other circulating antibody responses have been associated with a decreased risk of infection, the correlates of protection against cholera have not been comprehensively compared. We aimed to analyse antibody-mediated correlates of protection from both V cholerae infection and cholera-related diarrhoea.

METHODS

We conducted a systems serology study that analysed 58 serum antibody biomarkers as correlates of protection against V cholerae O1 infection or diarrhoea. We used serum samples from two cohorts: household contacts of people with confirmed cholera in Dhaka, Bangladesh, and cholera-naive volunteers who were recruited at three centres in the USA, vaccinated with a single dose of CVD 103-HgR live oral cholera vaccine, and then challenged with V cholerae O1 El Tor Inaba strain N16961. We measured antigen-specific immunoglobulin responses against antigens using a customised Luminex assay and used conditional random forest models to examine which baseline biomarkers were most important for classifying individuals who went on to develop infection versus those who remained uninfected or asymptomatic. V cholerae infection was defined as having a positive stool culture result on days 2-7 or day 30 after enrolment of the household's index cholera case and, in the vaccine challenge cohort, was the development of symptomatic diarrhoea (defined as two or more loose stools of ≥200 mL each, or a single loose stool of ≥300 mL over a 48-h period).

FINDINGS

In the household contact cohort (261 participants from 180 households), 20 (34%) of the 58 studied biomarkers were associated with protection against V cholerae infection. We identified serum antibody-dependent complement deposition targeting the O1 antigen as the most predictive correlate of protection from infection in the household contacts, whereas vibriocidal antibody titres ranked lower. A five-biomarker model predicted protection from V cholerae infection with a cross-validated area under the curve (cvAUC) of 79% (95% CI 73-85). This model also predicted protection against diarrhoea in unvaccinated volunteers challenged with V cholerae O1 after vaccination (n=67; area under the curve [AUC] 77%, 95% CI 64-90). Although a different five-biomarker model best predicted protection from the development of cholera diarrhoea in the challenged vaccinees (cvAUC 78%, 95% CI 66-91), this model did poorly at predicting protection against infection in the household contacts (AUC 60%, 52-67).

INTERPRETATION

Several biomarkers predict protection better than vibriocidal titres. A model based on protection against infection among household contacts was predictive of protection against both infection and diarrhoeal illness in challenged vaccinees, suggesting that models based on observed conditions in a cholera-endemic population might be more likely to identify broadly applicable correlates of protection than models trained on single experimental settings.

FUNDING

National Institute of Allergy and Infectious Diseases and National Institute of Child Health and Human Development, National Institutes of Health.

Pre-existing Fc profiles shape the evolution of neutralizing antibody breadth following influenza vaccination

Under the ever-present threat of a pandemic influenza strain, the evolution of a broadly reactive, neutralizing, functional, humoral immune response may hold the key to protection against both circulating and emerging influenza strains. We apply a systems approach to profile hemagglutinin- and neuraminidase-specific humoral signatures that track with the evolution of broad immunity in a cohort of vaccinated individuals and validate these findings in a second longitudinal cohort. Multivariate analysis reveals the presence of a unique pre-existing Fcγ-receptor-binding antibody profile in individuals that evolved broadly reactive hemagglutination inhibition activity (HAI), marked by the presence of elevated levels of pre-existing FCGR2B-binding antibodies. Moreover, vaccination with FCGR2B-binding antibody-opsonized influenza results in enhanced antibody titers and HAI activity in a murine model. Together, these data suggest that pre-existing FCGR2B binding antibodies are a key correlate of the evolution of broadly protective influenza-specific antibodies, providing insight for the design of next-generation influenza vaccines.

Defining the determinants of protection against SARS-CoV-2 infection and viral control in a dose-down Ad26.CoV2.S vaccine study in nonhuman primates

Despite the rapid creation of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) vaccines, the precise correlates of immunity against severe Coronavirus Disease 2019 (COVID-19) are still unknown. Neutralizing antibodies represent a robust surrogate of protection in early Phase III studies, but vaccines provide protection prior to the evolution of neutralization, vaccines provide protection against variants that evade neutralization, and vaccines continue to provide protection against disease severity in the setting of waning neutralizing titers. Thus, in this study, using an Ad26.CoV2.S dose-down approach in nonhuman primates (NHPs), the role of neutralization, Fc effector function, and T-cell immunity were collectively probed against infection as well as against viral control. While dosing-down minimally impacted neutralizing and binding antibody titers, Fc receptor binding and functional antibody levels were induced in a highly dose-dependent manner. Neutralizing antibody and Fc receptor binding titers, but minimally T cells, were linked to the prevention of transmission. Conversely, Fc receptor binding/function and T cells were linked to antiviral control, with a minimal role for neutralization. These data point to dichotomous roles of neutralization and T-cell function in protection against transmission and disease severity and a continuous role for Fc effector function as a correlate of immunity key to halting and controlling SARS-CoV-2 and emerging variants.

Functional compartmentalization of antibodies in the central nervous system during chronic HIV infection

The central nervous system (CNS) has emerged as a critical HIV reservoir. Thus, interventions aimed at controlling and eliminating HIV must include CNS-targeted strategies. Given the inaccessibility of the brain, efforts have focused on cerebrospinal fluid (CSF), aimed at defining biomarkers of HIV-disease in the CNS, including HIV-specific antibodies. However, how antibodies traffic between the blood and CNS, and whether specific antibody profiles track with HIV-associated neurocognitive disorders (HAND) remains unclear. Here, we comprehensively profiled HIV-specific antibodies across plasma and CSF from 20 antiretroviral therapy (ART) naive or treated persons with HIV. CSF was populated by IgG1 and IgG3 antibodies, with reduced Fc-effector profiles. While ART improved plasma antibody functional coordination, CSF profiles were unaffected by ART and were unrelated to HAND severity. These data point to a functional sieving of antibodies across the blood-brain barrier, providing previously unappreciated insights for the development of next-generation therapeutics targeting the CNS reservoir.

Serological Markers of SARS-CoV-2 Reinfection

As public health guidelines throughout the world have relaxed in response to vaccination campaigns against SARS-CoV-2, it is likely that SARS-CoV-2 will remain endemic, fueled by the rise of more infectious SARS-CoV-2 variants. Moreover, in the setting of waning natural and vaccine immunity, reinfections have emerged across the globe, even among previously infected and vaccinated individuals. As such, the ability to detect reexposure to and reinfection by SARS-CoV-2 is a key component for global protection against this virus and, more importantly, against the potential emergence of vaccine escape mutations. Accordingly, there is a strong and continued need for the development and deployment of simple methods to detect emerging hot spots of reinfection to inform targeted pandemic response and containment, including targeted and specific deployment of vaccine booster campaigns. In this study, we identify simple, rapid immune biomarkers of reinfection in rhesus macaques, including IgG3 antibody levels against nucleocapsid and FcγR2A receptor binding activity of anti-RBD antibodies, that are recapitulated in human reinfection cases. As such, this cross-species analysis underscores the potential utility of simple antibody titers and function as price-effective and scalable markers of reinfection to provide increased resolution and resilience against new outbreaks. IMPORTANCE As public health and social distancing guidelines loosen in the setting of waning global natural and vaccine immunity, a deeper understanding of the immunological response to reexposure and reinfection to this highly contagious pathogen is necessary to maintain public health. Viral sequencing analysis provides a robust but unrealistic means to monitor reinfection globally. The identification of scalable pathogen-specific biomarkers of reexposure and reinfection, however, could significantly accelerate our capacity to monitor the spread of the virus through naive and experienced hosts, providing key insights into mechanisms of disease attenuation. Using a nonhuman primate model of controlled SARS-CoV-2 reexposure, we deeply probed the humoral immune response following rechallenge with various doses of viral inocula. We identified virus-specific humoral biomarkers of reinfection, with significant increases in antibody titer and function upon rechallenge across a range of humoral features, including IgG1 to the receptor binding domain of the spike protein of SARS-CoV-2 (RBD), IgG3 to the nucleocapsid protein (N), and FcγR2A receptor binding to anti-RBD antibodies. These features not only differentiated primary infection from reexposure and reinfection in monkeys but also were recapitulated in a sequencing-confirmed reinfection patient and in a cohort of putatively reinfected humans that evolved a PCR-positive test in spite of preexisting seropositivity. As such, this cross-species analysis using a controlled primate model and human cohorts reveals increases in antibody titers as promising cross-validated serological markers of reinfection and reexposure.

Reduced antibody activity against SARS-CoV-2 B.1.617.2 delta virus in serum of mRNA-vaccinated individuals receiving tumor necrosis factor-α inhibitors

BACKGROUND

Although vaccines effectively prevent coronavirus disease 2019 (COVID-19) in healthy individuals, they appear to be less immunogenic in individuals with chronic inflammatory disease (CID) or receiving chronic immunosuppression therapy.

METHODS

Here we assessed a cohort of 77 individuals with CID treated as monotherapy with chronic immunosuppressive drugs for antibody responses in serum against historical and variant severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viruses after immunization with the BNT162b2 mRNA vaccine.

FINDINGS

Longitudinal analysis showed the greatest reductions in neutralizing antibodies and Fc effector function capacity in individuals treated with tumor necrosis factor alpha (TNF-α) inhibitors (TNFi), and this pattern appeared to be worse against the B.1.617.2 delta virus. Within 5 months of vaccination, serum neutralizing titers of all TNFi-treated individuals tested fell below the presumed threshold correlate for antibody-mediated protection. However, TNFi-treated individuals receiving a third mRNA vaccine dose boosted their serum neutralizing antibody titers by more than 16-fold.

CONCLUSIONS

Vaccine boosting or administration of long-acting prophylaxis (e.g., monoclonal antibodies) will likely be required to prevent SARS-CoV-2 infection in this susceptible population.

FUNDING

This study was supported by grants and contracts from the NIH (R01 AI157155, R01AI151178, and HHSN75N93019C00074; NIAID Centers of Excellence for Influenza Research and Response (CEIRR) contracts HHSN272201400008C and 75N93021C00014; and Collaborative Influenza Vaccine Innovation Centers [CIVIC] contract 75N93019C00051).

Epidemiological and Immunological Features of Obesity and SARS-CoV-2

Obesity is a key correlate of severe SARS-CoV-2 outcomes while the role of obesity on risk of SARS-CoV-2 infection, symptom phenotype, and immune response remain poorly defined. We examined data from a prospective SARS-CoV-2 cohort study to address these questions. Serostatus, body mass index, demographics, comorbidities, and prior COVID-19 compatible symptoms were assessed at baseline and serostatus and symptoms monthly thereafter. SARS-CoV-2 immunoassays included an IgG ELISA targeting the spike RBD, multiarray Luminex targeting 20 viral antigens, pseudovirus neutralization, and T cell ELISPOT assays. Our results from a large prospective SARS-CoV-2 cohort study indicate symptom phenotype is strongly influenced by obesity among younger but not older age groups; we did not identify evidence to suggest obese individuals are at higher risk of SARS-CoV-2 infection; and remarkably homogenous immune activity across BMI categories suggests immune protection across these groups may be similar.

Early cross-coronavirus reactive signatures of humoral immunity against COVID-19

The introduction of vaccines has inspired hope in the battle against SARS-CoV-2. However, the emergence of viral variants, in the absence of potent antivirals, has left the world struggling with the uncertain nature of this disease. Antibodies currently represent the strongest correlate of immunity against SARS-CoV-2, thus we profiled the earliest humoral signatures in a large cohort of acutely ill (survivors and nonsurvivors) and mild or asymptomatic individuals with COVID-19. Although a SARS-CoV-2–specific immune response evolved rapidly in survivors of COVID-19, nonsurvivors exhibited blunted and delayed humoral immune evolution, particularly with respect to S2-specific antibodies. Given the conservation of S2 across β-coronaviruses, we found that the early development of SARS-CoV-2–specific immunity occurred in tandem with preexisting common β-coronavirus OC43 humoral immunity in survivors, which was also selectively expanded in individuals that develop a paucisymptomatic infection. These data point to the importance of cross-coronavirus immunity as a correlate of protection against COVID-19.

Fab and Fc contribute to maximal protection against SARS-CoV-2 following NVX-CoV2373 subunit vaccine with Matrix-M vaccination

Recently approved vaccines have shown remarkable efficacy in limiting SARS-CoV-2-associated disease. However, with the variety of vaccines, immunization strategies, and waning antibody titers, defining the correlates of immunity across a spectrum of antibody titers is urgently required. Thus, we profiled the humoral immune response in a cohort of non-human primates immunized with a recombinant SARS-CoV-2 spike glycoprotein (NVX-CoV2373) at two doses, administered as a single- or two-dose regimen. Both antigen dose and boosting significantly altered neutralization titers and Fc-effector profiles, driving unique vaccine-induced antibody fingerprints. Combined differences in antibody effector functions and neutralization were associated with distinct levels of protection in the upper and lower respiratory tract. Moreover, NVX-CoV2373 elicited antibodies that functionally targeted emerging SARS-CoV-2 variants. Collectively, the data presented here suggest that a single dose may prevent disease via combined Fc/Fab functions but that two doses may be essential to block further transmission of SARS-CoV-2 and emerging variants.

An intranasal vaccine durably protects against SARS-CoV-2 variants in mice

SARS-CoV-2 variants that attenuate antibody neutralization could jeopardize vaccine efficacy. We recently reported the protective activity of an intranasally administered spike protein-based chimpanzee adenovirus-vectored vaccine (ChAd-SARS-CoV-2-S) in animals, which has advanced to human trials. Here, we assessed its durability, dose response, and cross-protective activity in mice. A single intranasal dose of ChAd-SARS-CoV-2-S induced durably high neutralizing and Fc effector antibody responses in serum and S-specific IgG and IgA secreting long-lived plasma cells in the bone marrow. Protection against a historical SARS-CoV-2 strain was observed across a 100-fold vaccine dose range and over a 200-day period. At 6 weeks or 9 months after vaccination, serum antibodies neutralized SARS-CoV-2 strains with B.1.351, B.1.1.28, and B.1.617.1 spike proteins and conferred almost complete protection in the upper and lower respiratory tracts after challenge with variant viruses. Thus, in mice, intranasal immunization with ChAd-SARS-CoV-2-S provides durable protection against historical and emerging SARS-CoV-2 strains.

Protective antibodies elicited by SARS-CoV-2 spike protein vaccination are boosted in the lung after challenge in nonhuman primates

Protein subunit–based vaccines have been used extensively for protection against viral infections. Here, Francica et al. tested a protein subunit vaccine for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The authors vaccinated nonhuman primates with soluble prefusion-stabilized spike trimers (preS dTM) plus the adjuvant AS03, an oil-in-water emulsion. The authors found that preS dTM plus AS03 induced robust antibody and cellular immune responses that protected nonhuman primates from disease when challenged with SARS-CoV-2. This rapid protection, with increases in antibodies specific to spike protein observable as soon as 2 days after infection, provides evidence of a critical anamnestic antibody response. Antibodies elicited by preS dTM vaccination are protective against SARS-CoV-2 in nonhuman primates.

Adjuvanted soluble protein vaccines have been used extensively in humans for protection against various viral infections based on their robust induction of antibody responses. Here, soluble prefusion-stabilized spike protein trimers (preS dTM) from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were formulated with the adjuvant AS03 and administered twice to nonhuman primates (NHPs). Binding and functional neutralization assays and systems serology revealed that the vaccinated NHP developed AS03-dependent multifunctional humoral responses that targeted distinct domains of the spike protein and bound to a variety of Fc receptors mediating immune cell effector functions in vitro. The neutralizing 50% inhibitory concentration titers for pseudovirus and live SARS-CoV-2 were higher than titers for a panel of human convalescent serum samples. NHPs were challenged intranasally and intratracheally with a high dose (3 × 10⁶ plaque forming units) of SARS-CoV-2 (USA-WA1/2020 isolate). Two days after challenge, vaccinated NHPs showed rapid control of viral replication in both the upper and lower airways. Vaccinated NHPs also had increased spike protein–specific immunoglobulin G (IgG) antibody responses in the lung as early as 2 days after challenge. Moreover, passive transfer of vaccine-induced IgG to hamsters mediated protection from subsequent SARS-CoV-2 challenge. These data show that antibodies induced by the AS03-adjuvanted preS dTM vaccine were sufficient to mediate protection against SARS-CoV-2 in NHPs and that rapid anamnestic antibody responses in the lung may be a key mechanism for protection.

Early cross-coronavirus reactive signatures of protective humoral immunity against COVID-19

The introduction of vaccines has inspired new hope in the battle against SARS-CoV-2. However, the emergence of viral variants, in the absence of potent antivirals, has left the world struggling with the uncertain nature of this disease. Antibodies currently represent the strongest correlate of immunity against COVID-19, thus we profiled the earliest humoral signatures in a large cohort of severe and asymptomatic COVID-19 individuals. While a SARS-CoV-2-specific immune response evolved rapidly in survivors of COVID-19, non-survivors exhibited blunted and delayed humoral immune evolution, particularly with respect to S2-specific antibody evolution. Given the conservation of S2 across β-coronaviruses, we found the early development of SARS-CoV-2-specific immunity occurred in tandem with pre-existing common β-coronavirus OC43 humoral immunity in survivors, which was selectively also expanded in individuals that develop paucisymptomatic infection. These data point to the importance of cross-coronavirus immunity as a correlate of protection against COVID-19.

Non-neutralizing Antibodies May Contribute to Suppression of SIVmac239 Viremia in Indian Rhesus Macaques

The antiviral properties of broadly neutralizing antibodies against HIV are well-documented but no vaccine is currently able to elicit protective titers of these responses in primates. While current vaccine modalities can readily induce non-neutralizing antibodies against simian immunodeficiency virus (SIV) and HIV, the ability of these responses to restrict lentivirus transmission and replication remains controversial. Here, we investigated the antiviral properties of non-neutralizing antibodies in a group of Indian rhesus macaques (RMs) that were vaccinated with vif, rev, tat, nef, and env, as part of a previous study conducted by our group. These animals manifested rapid and durable control of viral replication to below detection limits shortly after SIVmac239 infection. Although these animals had no serological neutralizing activity against SIVmac239 prior to infection, their pre-challenge titers of Env-binding antibodies correlated with control of viral replication. To assess the contribution of anti-Env humoral immune responses to virologic control in two of these animals, we transiently depleted their circulating antibodies via extracorporeal plasma immunoadsorption and inhibition of IgG recycling through antibody-mediated blockade of the neonatal Fc receptor. These procedures reduced Ig serum concentrations by up to 80% and temporarily induced SIVmac239 replication in these animals. Next, we transferred purified total Ig from the rapid controllers into six vaccinated RMs one day before intrarectal challenge with SIVmac239. Although recipients of the hyperimmune anti-SIV Ig fraction were not protected from infection, their peak and chronic phase viral loads were significantly lower than those in concurrent unvaccinated control animals. Together, our results suggest that non-neutralizing Abs may play a role in the suppression of SIVmac239 viremia.

Vaccination with SARS-CoV-2 Spike Protein and AS03 Adjuvant Induces Rapid Anamnestic Antibodies in the Lung and Protects Against Virus Challenge in Nonhuman Primates

Adjuvanted soluble protein vaccines have been used extensively in humans for protection against various viral infections based on their robust induction of antibody responses. Here, soluble prefusion-stabilized spike trimers (preS dTM) from the severe acute respiratory syndrome coronavirus (SARS-CoV-2) were formulated with the adjuvant AS03 and administered twice to nonhuman primates (NHP). Binding and functional neutralization assays and systems serology revealed that NHP developed AS03-dependent multi-functional humoral responses that targeted multiple spike domains and bound to a variety of antibody FC receptors mediating effector functions in vitro. Pseudovirus and live virus neutralizing IC50 titers were on average greater than 1000 and significantly higher than a panel of human convalescent sera. NHP were challenged intranasally and intratracheally with a high dose (3×106 PFU) of SARS-CoV-2 (USA-WA1/2020 isolate). Two days post-challenge, vaccinated NHP showed rapid control of viral replication in both the upper and lower airways. Notably, vaccinated NHP also had increased spike-specific IgG antibody responses in the lung as early as 2 days post challenge. Moreover, vaccine-induced IgG mediated protection from SARS-CoV-2 challenge following passive transfer to hamsters. These data show that antibodies induced by the AS03-adjuvanted preS dTM vaccine are sufficient to mediate protection against SARS-CoV-2 and support the evaluation of this vaccine in human clinical trials.

Discrete SARS-CoV-2 antibody titers track with functional humoral stability

Antibodies serve as biomarkers of infection, but if sustained can confer long-term immunity. Yet, for most clinically approved vaccines, binding antibody titers only serve as a surrogate of protection. Instead, the ability of vaccine induced antibodies to neutralize or mediate Fc-effector functions is mechanistically linked to protection. While evidence has begun to point to persisting antibody responses among SARS-CoV-2 infected individuals, cases of re-infection have begun to emerge, calling the protective nature of humoral immunity against this highly infectious pathogen into question. Using a community-based surveillance study, we aimed to define the relationship between titers and functional antibody activity to SARS-CoV-2 over time. Here we report significant heterogeneity, but limited decay, across antibody titers amongst 120 identified seroconverters, most of whom had asymptomatic infection. Notably, neutralization, Fc-function, and SARS-CoV-2 specific T cell responses were only observed in subjects that elicited RBD-specific antibody titers above a threshold. The findings point to a switch-like relationship between observed antibody titer and function, where a distinct threshold of activity-defined by the level of antibodies-is required to elicit vigorous humoral and cellular response. This response activity level may be essential for durable protection, potentially explaining why re-infections occur with SARS-CoV-2 and other common coronaviruses.

Collaboration between the Fab and Fc contribute to maximal protection against SARS-CoV-2 in nonhuman primates following NVX-CoV2373 subunit vaccine with Matrix-M™ vaccination

Recently approved vaccines have already shown remarkable protection in limiting SARS-CoV-2 associated disease. However, immunologic mechanism(s) of protection, as well as how boosting alters immunity to wildtype and newly emerging strains, remain incompletely understood. Here we deeply profiled the humoral immune response in a cohort of non-human primates immunized with a stable recombinant full-length SARS-CoV-2 spike (S) glycoprotein (NVX-CoV2373) at two dose levels, administered as a single or two-dose regimen with a saponin-based adjuvant Matrix-M™. While antigen dose had some effect on Fc-effector profiles, both antigen dose and boosting significantly altered overall titers, neutralization and Fc-effector profiles, driving unique vaccine-induced antibody fingerprints. Combined differences in antibody effector functions and neutralization were strongly associated with distinct levels of protection in the upper and lower respiratory tract, pointing to the presence of combined, but distinct, compartment-specific neutralization and Fc-mechanisms as key determinants of protective immunity against infection. Moreover, NVX-CoV2373 elicited antibodies functionally target emerging SARS-CoV-2 variants, collectively pointing to the critical collaborative role for Fab and Fc in driving maximal protection against SARS-CoV-2. Collectively, the data presented here suggest that a single dose may prevent disease, but that two doses may be essential to block further transmission of SARS-CoV-2 and emerging variants.

HIGHLIGHTS

NVX-CoV2373 subunit vaccine elicits receptor blocking, virus neutralizing antibodies, and Fc-effector functional antibodies.The vaccine protects against respiratory tract infection and virus shedding in non-human primates (NHPs).Both neutralizing and Fc-effector functions contribute to protection, potentially through different mechanisms in the upper and lower respiratory tract.Both macaque and human vaccine-induced antibodies exhibit altered Fc-receptor binding to emerging mutants.

Epidemiological and immunological features of obesity and SARS-CoV-2

Obesity is a key correlate of severe SARS-CoV-2 outcomes while the role of obesity on risk of SARS-CoV-2 infection, symptom phenotype, and immune response are poorly defined. We examined data from a prospective SARS-CoV-2 cohort study to address these questions. Serostatus, body mass index, demographics, comorbidities, and prior COVID-19 compatible symptoms were assessed at baseline and serostatus and symptoms monthly thereafter. SARS-CoV-2 immunoassays included an IgG ELISA targeting the spike RBD, multiarray Luminex targeting 20 viral antigens, pseudovirus neutralization, and T cell ELISPOT assays. Our results from a large prospective SARS-CoV-2 cohort study indicate symptom phenotype is strongly influenced by obesity among younger but not older age groups; we did not identify evidence to suggest obese individuals are at higher risk of SARS-CoV-2 infection; and, remarkably homogenous immune activity across BMI categories suggests natural- and vaccine-induced protection may be similar across these groups.

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.

Fc Glycan-Mediated Regulation of Placental Antibody Transfer

Despite the worldwide success of vaccination, newborns remain vulnerable to infections. While neonatal vaccination has been hampered by maternal antibody-mediated dampening of immune responses, enhanced regulatory and tolerogenic mechanisms, and immune system immaturity, maternal pre-natal immunization aims to boost neonatal immunity via antibody transfer to the fetus. However, emerging data suggest that antibodies are not transferred equally across the placenta. To understand this, we used systems serology to define Fc features associated with antibody transfer. The Fc-profile of neonatal and maternal antibodies differed, skewed toward natural killer (NK) cell-activating antibodies. This selective transfer was linked to digalactosylated Fc-glycans that selectively bind FcRn and FCGR3A, resulting in transfer of antibodies able to efficiently leverage innate immune cells present at birth. Given emerging data that vaccination may direct antibody glycosylation, our study provides insights for the development of next-generation maternal vaccines designed to elicit antibodies that will most effectively aid neonates.

Antigen-specific antibody Fc glycosylation enhances humoral immunity via the recruitment of complement

HIV-specific broadly neutralizing antibodies (bNAbs) confer protection after passive immunization, but the immunological mechanisms that drive their development are poorly understood. Structural features of bNAbs indicate that they originate from extensive germinal center (GC) selection, which relies on persistent GC activity. However, why a fraction of infected individuals are able to successfully drive more effective affinity maturation is unclear. Delivery of antigens in the form of antibody-immune complexes (ICs), which bind to complement receptors (CRs) or Fc receptors (FcRs) on follicular dendritic cells, represents an effective mechanism for antigen delivery to the GC. We sought to define whether IC-FcR or CR interactions differ among individuals who develop bNAb responses to HIV. Enhanced Fc effector functions and FcR/CR interactions, via altered Fc glycosylation profiles, were observed among individuals with neutralizing antibody responses to HIV compared with those without neutralizing antibody activity. Moreover, both polyclonal neutralizer ICs and monoclonal IC mimics of neutralizer antibodies induced higher antibody titers, higher-avidity antibodies, and expanded GC B cell reactions after immunization of mice via accelerated antigen deposition within B cell follicles in a complement-dependent manner. Thus, these data point to a direct role for altered Fc profile/complement interactions in shaping the maturation of the humoral immune response, providing insights into how GC activity may be enhanced to drive affinity maturation in next-generation vaccine approaches.

An Immunocompetent Mouse Model of Zika Virus Infection

Progress toward understanding Zika virus (ZIKV) pathogenesis is hindered by lack of immunocompetent small animal models, in part because ZIKV fails to effectively antagonize Stat2-dependent interferon (IFN) responses in mice. To address this limitation, we first passaged an African ZIKV strain (ZIKV-Dak-41525) through Rag1-/- mice to obtain a mouse-adapted virus (ZIKV-Dak-MA) that was more virulent than ZIKV-Dak-41525 in mice treated with an anti-Ifnar1 antibody. A G18R substitution in NS4B was the genetic basis for the increased replication, and resulted in decreased IFN-β production, diminished IFN-stimulated gene expression, and the greater brain infection observed with ZIKV-Dak-MA. To generate a fully immunocompetent mouse model of ZIKV infection, human STAT2 was introduced into the mouse Stat2 locus (hSTAT2 KI). Subcutaneous inoculation of pregnant hSTAT2 KI mice with ZIKV-Dak-MA resulted in spread to the placenta and fetal brain. An immunocompetent mouse model of ZIKV infection may prove valuable for evaluating countermeasures to limit disease.

Dengue virus-reactive CD8+ T cells mediate cross-protection against subsequent Zika virus challenge

Zika virus (ZIKV) and dengue virus (DENV) are antigenically related flaviviruses that share cross-reactivity in antibody and T cell responses, and co-circulate in increasing numbers of countries. Whether pre-existing DENV immunity can cross-protect or enhance ZIKV infection during sequential infection of the same host is unknown. Here, we show that DENV-immune Ifnar1^−/− or wild-type C57BL/6 mice infected with ZIKV have cross-reactive immunity to subsequent ZIKV infection and pathogenesis. Adoptive transfer and cell depletion studies demonstrate that DENV-immune CD8⁺ T cells predominantly mediate cross-protective responses to ZIKV. In contrast, passive transfer studies suggest that DENV-immune serum does not protect against ZIKV infection. Thus, CD8⁺ T cell immunity generated during primary DENV infection can confer protection against secondary ZIKV infection in mice. Further optimization of current DENV vaccines for T cell responses might confer cross-protection and prevent antibody-mediated enhancement of ZIKV infection.

Dengue virus-specific antibody and CD8⁺ T cells that cross-react with Zika virus have been described. Here, the authors establish a functionally protective role for cross-reactive dengue virus-specific CD8⁺ T cells during challenge with Zika virus.

Zika virus has oncolytic activity against glioblastoma stem cells

Glioblastoma is a highly lethal brain cancer that frequently recurs in proximity to the original resection cavity. We explored the use of oncolytic virus therapy against glioblastoma with Zika virus (ZIKV), a flavivirus that induces cell death and differentiation of neural precursor cells in the developing fetus. ZIKV preferentially infected and killed glioblastoma stem cells (GSCs) relative to differentiated tumor progeny or normal neuronal cells. The effects against GSCs were not a general property of neurotropic flaviviruses, as West Nile virus indiscriminately killed both tumor and normal neural cells. ZIKV potently depleted patient-derived GSCs grown in culture and in organoids. Moreover, mice with glioblastoma survived substantially longer and at greater rates when the tumor was inoculated with a mouse-adapted strain of ZIKV. Our results suggest that ZIKV is an oncolytic virus that can preferentially target GSCs; thus, genetically modified strains that further optimize safety could have therapeutic efficacy for adult glioblastoma patients.

Investigation of CD8+ T Cell Immunity in Zika Virus Infection Using Mouse Models

CD8+ T cells may play a dual role in both protection against and pathogenesis of Flaviviruses, including Zika virus (ZIKV). However, virtually nothing is currently known about the role CD8+ T cells play during ZIKV infection in humans and animal models. The goal of our study is to investigate the role of CD8+ T cells during primary ZIKV infection in mice. Using LysMCre+IFNARfl/fl C57BL/6 (H-2b) mice that lack type I IFN receptor in a subset of myeloid cells, we characterized a new mouse model susceptible to infection with both East African lineage (MR766) and Asian lineage (FSS13025) ZIKV strains. A screening of 244 ZIKV epitopes predicted to bind H-2b class I molecules, defined a specific map of 26 and 15 peptides for MR766 and FSS13025 ZIKV strains, respectively. Intracellular cytokine staining confirmed the identity of these epitopes and demonstrated induction of polyfunctional ZIKV-specific CD8+ T cells. Furthermore, adoptive transfer of ZIKV-immune CD8+ T cells reduced viral burdens, whereas depletion of CD8+ T cells led to higher tissue burdens and mortality was increased in ZIKV-infected CD8−/− mice compared to Wild-type. These results demonstrate that CD8+ T cells are important mediators of protection during primary ZIKV infection and provide a H-2b mouse model for investigating ZIKV-specific CD8+ T cell responses. Based on these findings, studies are in progress towards defining the role of resident memory CD8+ T cells in protection against ZIKV infection using our recently developed mouse models of ZIKV systemic infection and sexual transmission.

Mapping and Role of the CD8+ T Cell Response During Primary Zika Virus Infection in Mice

CD8+ T cells may play a dual role in protection against and pathogenesis of flaviviruses, including Zika virus (ZIKV). We evaluated the CD8+ T cell response in ZIKV-infected LysMCre+IFNARfl/fl C57BL/6 (H-2b) mice lacking the type I interferon receptor in a subset of myeloid cells. In total, 26 and 15 CD8+ T cell-reactive peptides for ZIKV African (MR766) and Asian (FSS13025) lineage strains, respectively, were identified and validated. CD8+ T cells from infected mice were polyfunctional and mediated cytotoxicity. Adoptive transfer of ZIKV-immune CD8+ T cells reduced viral burdens, whereas their depletion led to higher tissue burdens, and CD8-/- mice displayed higher mortality with ZIKV infection. Collectively, these results demonstrate that CD8+ T cells protect against ZIKV infection. Further, this study provides a T cell competent mouse model for investigating ZIKV-specific T cell responses.

Structural Basis of Zika Virus-Specific Antibody Protection

Zika virus (ZIKV) infection during pregnancy has emerged as a global public health problem because of its ability to cause severe congenital disease. Here, we developed six mouse monoclonal antibodies (mAbs) against ZIKV including four (ZV-48, ZV-54, ZV-64, and ZV-67) that were ZIKV specific and neutralized infection of African, Asian, and American strains to varying degrees. X-ray crystallographic and competition binding analyses of Fab fragments and scFvs defined three spatially distinct epitopes in DIII of the envelope protein corresponding to the lateral ridge (ZV-54 and ZV-67), C-C' loop (ZV-48 and ZV-64), and ABDE sheet (ZV-2) regions. In vivo passive transfer studies revealed protective activity of DIII-lateral ridge specific neutralizing mAbs in a mouse model of ZIKV infection. Our results suggest that DIII is targeted by multiple type-specific antibodies with distinct neutralizing activity, which provides a path for developing prophylactic antibodies for use in pregnancy or designing epitope-specific vaccines against ZIKV.

Drosophila host model reveals new enterococcus faecalis quorum-sensing associated virulence factors

Enterococcus faecalis V583 is a vancomycin-resistant clinical isolate which belongs to the hospital-adapted clade, CC2. This strain harbours several factors that have been associated with virulence, including the fsr quorum-sensing regulatory system that is known to control the expression of GelE and SprE proteases. To discriminate between genes directly regulated by Fsr, and those indirectly regulated as the result of protease expression or activity, we compared gene expression in isogenic mutants of V583 variously defective in either Fsr quorum sensing or protease expression. Quorum sensing was artificially induced by addition of the quorum signal, GBAP, exogenously in a controlled manner. The Fsr regulon was found to be restricted to five genes, gelE, sprE, ef1097, ef1351 and ef1352. Twelve additional genes were found to be dependent on the presence of GBAP-induced proteases. Induction of GelE and SprE by GBAP via Fsr resulted in accumulation of mRNA encoding lrgAB, and this induction was found to be lytRS dependent. Drosophila infection was used to discern varying levels of toxicity stemming from mutations in the fsr quorum regulatory system and the genes that it regulates, highlighting the contribution of LrgAB and bacteriocin EF1097 to infection toxicity. A contribution of SprE to infection toxicity was also detected. This work brought to light new players in E. faecalis success as a pathogen and paves the way for future studies on host tolerance mechanisms to infections caused by this important nosocomial pathogen.

Bacterial challenge stimulates innate immune responses in extra-embryonic tissues of tobacco hornworm eggs

Innate immunity protects juvenile and adult vertebrates and invertebrates against potential pathogens; however, it is unknown when developing embryos become immune competent and just how they are guarded from infection. To address these questions, we studied the effect of immune challenge on early stage eggs of the tobacco hornworm, Manduca sexta. We detected many immune-related proteins and mRNAs in naive eggs. Upon immune challenge, antimicrobial protein genes were up-regulated, and antibacterial activity increased. Antimicrobial protein mRNAs and lysozyme were present in the extra-embryonic tissues of immune-challenged eggs; in addition, melanization in response to bacteria occurred in the yolk but not embryonic tissues. We conclude that the extra-embryonic tissues of early stage M. sexta eggs are immune competent and likely protect the developing embryo from infection. We suggest that innate immune responses of extra-embryonic tissues may be a common mechanism for protecting early embryos.

Differences in adhesion receptor expression between immature and older platelets and red blood cells of neonates and adults

PURPOSE

To examine the hypothesis that reticulated platelets and reticulocytes show elevated adhesion receptor expression compared with mature cells in both adult and neonatal cells.

METHODS

Flow cytometry was used to examine laminin, fibronectin (VLA-6), and thrombospondin (glycoprotein IV [GPIV]) expression in reticulated red cells, reticulated platelets, and older peripherally circulating mature red cells and mature platelets in seven newborn cord blood samples and blood samples from eight adult volunteers.

RESULTS

The difference in the neonatal reticulated platelet percentage of 9.2+/-14.8% was not statistically significant from the adult reticulated platelet percentage of 5.0+/-1.5% in this small population. There was a statistically significant difference between the reticulated cord blood red cell mean of 7.7+/-1.8% and the adult mean of 3.1+/-0.43%. Mean expression of VLA-6 was 96% in adult reticulated platelets, 79% in adult mature platelets, 81% in cord reticulated platelets and 65% in cord mature platelets. Mean expression of GPIV was similar, with corresponding values of 90%, 71%, 78%, and 57%. Reticulated red cells in adults averaged 44% VLA-4 and 46% GPIV; cord reticulocytes were 9% and 15%, respectively.

CONCLUSIONS

Reticulated cells newly released from the bone marrow express more adhesive receptors than mature cells in both groups. Cord blood samples showed hypoexpression of both receptor types in red blood cells and platelets.

Serine proteases as mediators of mosquito immune responses

Serine proteases regulate several invertebrate defense responses, including hemolymph coagulation, antimicrobial peptide synthesis, and melanization of pathogen surfaces. These processes require the presence of serine proteases in the hemolymph where they can rapidly activate immune pathways in response to pathogen detection. Hemolymph coagulation in the horseshoe crab is controlled by several serine proteases, including two that are pathogen recognition molecules and two in the clip domain family of serine proteases. The antimicrobial peptide synthesis and melanization pathways include clip domain proteases as well as other, uncharacterized serine proteases. We have identified five serine proteases from the hemolymph of the mosquito, Anopheles gambiae. One, Sp22D, is a large protease with potential pathogen binding domains. Sp22D is expressed in three tissues that have immune functions (midgut epithelium, fat body, and hemocytes), and its transcript abundance increases after immune challenge. Sp14A, Sp14D1, and Sp14D2 are clip domain serine proteases that are similar to enzymes with presumed roles in melanization or antimicrobial peptide synthesis. They undergo changes in transcript abundance in response to infection with bacteria or malaria parasites, and they reside in a chromosomal region that has been associated with melanization of parasites. Sp18D, also a clip domain protease, is similar to a Manduca protease with a likely role in immunity, but immune challenge does not affect its mRNA abundance.

Sp22D: a multidomain serine protease with a putative role in insect immunity

Serine proteases play critical roles in a variety of insect immune responses; however, few of the genes that code for these enzymes have been cloned. Here, we describe the molecular characterization of a serine protease gene from the mosquito Anopheles gambiae. Sp22D codes for a 1322 amino acid polypeptide with a complex domain organization. In addition to the carboxy terminal serine protease catalytic domain, Sp22D contains two putative chitin binding domains, a mucin-like domain, two low density lipoprotein receptor class A domains, and two scavenger receptor cysteine rich domains. A typical signal peptide sequence and a lack of potential transmembrane helices suggest that Sp22D is secreted. Sp22D is expressed constitutively in three immune-related cell types: adult hemocytes, fat body cells, and midgut epithelial cells. Wounding induces no changes in transcript abundance, but within 1h after injection of bacteria, Sp22D mRNA increases 1.5-fold. Based on domain organization, tissue distribution, and transcriptional up-regulation in response to immune challenge, we suggest that Sp22D has an immune function. In addition, we predict that Sp22D is secreted into the hemolymph where it may interact with pathogen surfaces and initiate an immune response.

Intravenous tissue plasminogen activator for acute ischemic stroke in patients aged 80 years and older : the tPA stroke survey experience

BACKGROUND AND PURPOSE

Intravenous tissue plasminogen activator (tPA) administered within 3 hours of symptom onset is the first available effective therapy for acute ischemic stroke (AIS). Few data exist, however, on its use in very elderly patients. We examined the characteristics, complications, and short-term outcome of AIS patients aged >/=80 years treated with tPA.

METHODS

Patients aged >/=80 years (n=30) were compared with counterparts aged <80 years (n=159) included in the tPA Stroke Survey, a US retrospective survey of 189 consecutive AIS patients treated with intravenous tPA at 13 hospitals.

RESULTS

Risk of intracerebral hemorrhage (fatal, symptomatic, and total) was 3%, 3%, and 7% in the elderly age group and 2%, 6%, and 9%, respectively, in their younger counterparts (P=NS for all comparisons). Likelihood of favorable outcome, defined as modified Rankin score 0 to 1, National Institutes of Health Stroke Scale score </=5, or marked improvement by hospital discharge, was comparable between groups (37%, 54%, and 43% versus 30%, 54%, and 43%, respectively; P=NS for all comparisons). Elderly patients were more likely to be treated by stroke specialists (87% versus 60%; P=0.005) and less likely to have an identified protocol deviation (13% versus 33%; P=0.03). Elderly patients were discharged more often to nursing care facilities (17% versus 5%; P=0.003). In logistic regression models there were no differences in odds ratio for favorable or poor outcome, other than tendency for higher in-hospital mortality in elderly patients (odds ratio, 2.8; 95% CI, 0.81 to 9.62; P=0.10).

CONCLUSIONS

Among AIS patients treated with intravenous tPA, age-related differences in characteristics and disposition were identified. No evidence for withholding tPA treatment for AIS in appropriately selected patients aged >/=80 years was identified.

Molecular characterization of five serine protease genes cloned from Anopheles gambiae hemolymph

We identified five new serine protease cDNAs from the hemolymph of the malaria vector, Anopheles gambiae. All five show sequence similarity to genes thought to be involved in vertebrate or invertebrate defense responses. Sp14A, Sp14D2 and Sp22D demonstrate changes in transcript abundance in response to bacteria injections. Sp14A and Sp14D2, as well as the previously characterized Sp14D1, are induced by infection with the malaria parasite, Plasmodium berghei. These three proteases, along with Sp18D, are related to a group of secreted proteases that have amino-terminal clip domains and trypsin-like substrate specificity. BLAST results and phylogenetic analyses group Sp14A, Sp14D1 and Sp14D2 with the Drosophila protease EASTER, and three prophenoloxidase activating enzymes from other insects. EASTER's substrate is SPAETZLE, a ligand involved in embryogenesis but also in activating anti-microbial peptide synthesis. Their similarity to EASTER and immune inducibility suggest that one of these proteases may activate a SPAETZLE-like ligand during anti-parasite responses in mosquitoes. Alternatively, as potential prophenoloxidase activators, Sp14A, Sp14D1 or Sp14D2 may play a role in melanotic encapsulation of Plasmodium.

An easter-like serine protease from Anopheles gambiae exhibits changes in transcript abundance following immune challenge

The nucleotide and deduced amino acid sequence of a serine protease (AgSp14D1) from the human malaria vector, Anopheles gambiae, is presented. The gene product is a 360 amino acid protein that contains two domains and has the highest sequence similarity to the Drosophila melanogaster serine protease easter and to prophenol oxidase activating enzyme (pPAE) from Manduca sexta. The catalytic domain is at the carboxy terminus and has the conserved serine, histidine and aspartic acid residues found in serine proteases as well as six cysteines common to invertebrate enzymes. The amino terminus contains critical cysteines that define a clip (=disulphide knot) domain which places this gene product in a subfamily of regulatory serine proteases that includes not only easter and pPAE but also the Drosophila proteins masquerade, stubble and snake as well as proclotting enzyme and factor B from the horseshoe crab. In situ hybridization to the polytene chromosomes detects a single band at 14D and Southern analysis with a probe from the 5' end of the gene confirms the single copy status of this gene. Northern analysis reveals changes in transcript abundance during development and following blood feeding. Interestingly, this analysis also shows an increase in transcript levels following wounding or injection of bacteria.

Ataxic hemiparesis: critical appraisal of a lacunar syndrome

BACKGROUND AND PURPOSE

Ataxic hemiparesis is a well-recognized lacunar syndrome involving homolateral ataxia with accompanying corticospinal tract impairment. Despite 30 years of clinical experience there continues to be some doubt as to the defining clinical characteristics, precise neuroanatomic localization of the syndrome, and etiologic mechanisms.

METHODS

We now present 45 new cases that have been analyzed for clinico-radiologic correlation and etiology. Also, all published cases from the English literature known to the authors are reviewed.

RESULTS

We found that the clinical syndrome of ataxic hemiparesis accurately predicts a small deep infarction, generally in the pons or internal capsule. Sensory loss is highly associated with a capsular localization. We found that 47% of the cases were attributed to small-vessel disease, 11% to cardioembolism, and only 7% to artery-to-artery embolism (all in the basilar artery); 1 case was attributed to thrombocytosis, 1 to multiple sclerosis, and the rest either had negative or incomplete evaluation. Approximately two thirds of the infarctions occurred in patients with neuroimaging evidence of other ischemic brain lesions.

CONCLUSIONS

Ataxic hemiparesis is a distinct clinical syndrome that accurately predicts a small deep infarction, most commonly in the pons or internal capsule. Only sensory loss accurately predicts a capsular localization. Etiology in nearly half of the cases can be attributed to small-vessel disease. Furthermore, ataxic hemiparesis appears to be a good marker for generalized asymptomatic cerebrovascular disease.

Cloning and characterization of a serine protease from the human malaria vector, Anopheles gambiae

The nucleotide and deduced amino acid sequence of a serine protease (AgSp24D) from the human malaria vector, Anopheles gambiae, is presented. The gene product is a 271 amino acid protein that contains the conserved serine, histidine and aspartic acid residues found in serine proteases, and has the highest identity to a serine protease of unknown function from Drosophila melanogaster. In situ hybridization to the polytene chromosomes detects a single band at 24D. Northern analysis reveals only low levels of transcripts in larvae and pupae, but more abundant transcription products occur in adults. Interestingly, this analysis also shows that adult males express much higher levels of AgSp24D mRNA than females. In addition, Plasmodium-refractory mosquitoes express higher levels of AgSp24D mRNA than susceptible mosquitoes although the biological significance of this remains to be examined. The thorax is the primary site for expression in the adults. The lack of a dramatic increase in AgSp24D mRNA levels following blood feeding suggests that this protease is not involved in digestive processes. Transcriptional induction does not follow cold shock, septic wounding, bacterial injection, laminarin injection or CM-Sephadex bead injection.

Mapping a quantitative trait locus involved in melanotic encapsulation of foreign bodies in the malaria vector, Anopheles gambiae

A Plasmodium-refractory strain of Anopheles gambiae melanotically encapsulates many species of Plasmodium, whereas wild-type mosquitoes are usually susceptible. This encapsulation trait can also be observed by studying the response of refractory and susceptible strains to intrathoracically injected CM-Sephadex beads. We report the results of broad-scale quantitative trait locus (QTL) mapping of the encapsulation trait using the bead model system. Interval mapping using the method of maximum likelihood identified one major QTL, Pen1. The 13.7-cM interval containing Pen1 was defined by marker AGH157 at 8E and AGH46 at 7A on 2R. Pen1 was associated with a maximum LOD score of 9.0 and accounted for 44% of the phenotypic variance in the distribution of phenotypes in the backcross. To test if this QTL is important for encapsulation of Plasmodium berghei, F2 progeny were infected with P. berghei and evaluated for degree of parasite encapsulation. For each of the two markers that define the interval containing Pen1, a significant difference of encapsulation was seen in progeny with at least one refractory allele in contrast with homozygous susceptible progeny. These results suggest that Pen1 is important for melanotic encapsulation of Plasmodium as well as beads.

A genetic study of a melanization response to Sephadex beads in Plasmodium-refractory and -susceptible strains of Anopheles gambiae

A previously selected Plasmodium-refractory strain of Anopheles gambiae melanotically encapsulates many species of Plasmodium. Genetic studies of this strain have shown that this refractory phenotype is controlled by a limited number of genes, and the existence of two such genes, Pif-B and Pif-C, has been demonstrated. Further work to determine the molecular basis for this mode of refractoriness led to the discovery that the host-parasite interaction is mimicked by the mosquito's response to carboxymethyl (CM)-Sephadex beads injected into the thorax. These small beads are melanized within 24 hr in refractory mosquitoes but are rarely melanized in susceptible ones. Because of the considerable potential in using bead melanization as a model for Plasmodium refractoriness, we performed a genetic analysis of the differential response to beads. Reciprocal crosses of susceptible (4arr) and refractory (L35) mosquitoes and an analysis of F1 phenotypes were done. The F1 progeny had a phenotype similar to that of the parental refractory mosquitoes; therefore, dominant refractory allele(s) must be present in the refractory strain. Males from the reciprocal crosses had identical phenotypes, indicating that X-linked loci did not have a visible effect on the melanizing phenotype. To further study the mode of inheritance of the melanizing trait, a backcross of F1 females to 4arr males was done. The phenotypic distribution of the backcross progeny was bimodal, and the melanization phenotypes were similar to those of the susceptible and refractory parents. These data suggest that a small number of loci are responsible for the differential response to CM-Sephadex beads, and that one chromosomal region contributes strongly to the melanizing trait. Because the 4arr strain carries mutations in the pink eye (X) and red eye (III) genes, possible linkage of the melanizing phenotype to these two genes was tested. No linkage with either marker was detected. The pattern of inheritance of the melanizing phenotype is similar to that of the refractory phenotype of Pif-B; therefore, the genetic basis of the two responses may be the same.

A shared genetic mechanism for melanotic encapsulation of CM-Sephadex beads and a malaria parasite, Plasmodium cynomolgi B, in the mosquito, Anopheles gambiae

A Plasmodium-refractory strain of Anopheles gambiae that melanizes ookinetes and intrathoracically inoculated CM-Sephadex beads was mated to a Plasmodium-susceptible strain that does not melanize the parasite or the beads. The F1 progeny were then backcrossed to the susceptible strain. Backcross progeny were given a blood meal containing infective Plasmodium cynomolgi B, and the parasites were allowed to develop for 6-7 days, at which time the infected mosquitoes were injected with CM-Sephadex beads. The next day the mosquitoes were dissected and the beads were scored for degree of melanization while the parasites were scored for degree of encapsulation. A Spearman rank order correlation test of the degree of correlation between the bead melanization phenotype and the parasite encapsulation phenotype gave a correlation coefficient of 0.74 (P < 0.01). This strong correlation between the two melanization responses suggests that the mechanisms for differential bead and parasite melanization of these two mosquito strains share at least one major gene.

Genetic analysis of embryonic cis-acting regulatory elements of the Drosophila homeotic gene sex combs reduced

The homeotic gene Sex combs reduced (Scr) of Drosophila melanogaster is expressed in the labial and prothoracic segments of the ectoderm, in parasegments two and three of the CNS, and in the visceral mesoderm of the anterior and posterior midgut. The mutationally defined function of Scr is to specify the identity of the labial and prothoracic segments and to control the development of the gastric caeca. The Scr locus occupies a chromosomal region of approximately 80 kb within the Antennapedia complex (ANT-C). To understand how Scr's spatiotemporal expression pattern is generated in the embryo, we have mapped its transcriptional regulatory elements using three approaches. First, we examined the expression pattern of Scr in embryos containing chromosomal rearrangements that remove potential Scr regulatory elements. Second, we made and analyzed a set of Scr minigene transformants. Third, we analyzed a set of Scr-lacZ enhancer tester constructs. Using more sensitive anti-SCR antisera, we discovered that Scr is expressed in tissues that were not previously thought to accumulate SCR: a stripe of ectodermal cells in the parasegment 2 region of stage 5 embryos, the embryonic salivary glands, and the dorsal ridge. Four DNA fragments that had previously been shown in an analysis of Scr-lacZ reporter constructs to contain putative Scr enhancer elements were found to have functional enhancers; similarly, another Scr fragment was found to contain a functional repressor. Our results suggest that regulation of Scr in the labial segment and the CNS requires the apparently synergistic action of multiple, widely spaced enhancer elements. Regulation in the prothorax also appears to be controlled by multiple enhancers:one complete pattern element and one subpattern element. In contrast, Scr regulation in the visceral mesoderm is controlled by an enhancer(s) located in only one DNA fragment.

A genetic analysis of deltex and its interaction with the Notch locus in Drosophila melanogaster

During Drosophila development networks of genes control the developmental pathways that specify cell fates. The Notch gene is a well characterized member of some cell fate pathways, and several other genes belonging to these same pathways have been identified because they share a neurogenic null phenotype with Notch. However, it is unlikely that the neurogenic genes represent all of the genes in these pathways. The goal of this research was to use a genetic approach to identify and characterize one of the other genes that acts with Notch to specify cell fate. Mutant alleles of genes in the same pathway should have phenotypes similar to Notch alleles and should show phenotypic interactions with Notch alleles. With this approach we identified the deltex gene as a potential cell fate gene. An extensive phenotypic characterization of loss-of-function deltex phenotypes showed abnormalities (such as thick wing veins, double bristles and extra cone cells) that suggest that deltex is involved in cell fate decision processes. Phenotypic interactions between deltex and Notch as seen in double mutants showed that Notch and deltex do not code for duplicate functions and that the two genes function together in many different developing tissues. The results of these investigations lead to the conclusion that the deltex gene functions with the Notch gene in one or more developmental pathways to specify cell fate.