Varicella-zoster virus antibody avidity and IgG-subclass patterns in children with recurrent chickenpox

An innate immune signature induced by AS01- or AS03-adjuvanted vaccines predicts the antibody response magnitude and quality consistently over time

Background

Antibody-mediated protection can depend on mechanisms varying from neutralization to Fc-dependent innate immune-cell recruitment. Adjuvanted vaccine development relies on a holistic understanding of how adjuvants modulate the quantity/titer and quality of the antibody response.

Methods

A Phase 2 trial (ClinicalTrials.gov: NCT00805389) evaluated hepatitis B vaccines formulated with licensed adjuvants (AS01B, AS01E, AS03, AS04 or Alum) in antigen-naïve adults. The trial investigated the role of adjuvants in shaping antibody-effector functions, and identified an innate transcriptional response shared by AS01B, AS01E and AS03. We integrated previously reported data on the innate response (gene expression, cytokine/C-reactive protein levels) and on quantitative/qualitative features of the mature antibody response (Fc-related parameters, immunoglobulin titers, avidity). Associations between the innate and humoral parameters were explored using systems vaccinology and a machine-learning framework.

Results

A dichotomy in responses between AS01/AS03 and AS04/Alum (with the former two contributing most to the association with the humoral response) was observed across all timepoints of this longitudinal study. The consistent patterns over time suggested a similarity in the impacts of the two-dose immunization regimen, year-long interval, and non-adjuvanted antigenic challenge given one year later. An innate signature characterized by interferon pathway-related gene expression and secreted interferon-γ-induced protein 10 and C-reactive protein, which was shared by AS01 and AS03, consistently predicted both the qualitative antibody response features and the titers. The signature also predicted from the antibody response quality, the group of adjuvants from which the administered vaccine was derived.

Conclusion

An innate signature induced by AS01- or AS03-adjuvanted vaccines predicts the antibody response magnitude and quality consistently over time.

Gestational Viral Infections: Role of Host Immune System

Viral infections in pregnancy are major causes of maternal and fetal morbidity and mortality. Infections can develop in the neonate transplacentally, perinatally, or postnatally (from breast milk or other sources) and lead to different clinical manifestations, depending on the viral agent and the gestational age at exposure. Viewing the peculiar tolerogenic status which characterizes pregnancy, viruses could exploit this peculiar immunological status to spread or affect the maternal immune system, adopting several evasion strategies. In fact, both DNA and RNA virus might have a deep impact on both innate and acquired immune systems. For this reason, investigating the interaction with these pathogens and the host's immune system during pregnancy is crucial not only for the development of most effective therapies and diagnosis but mostly for prevention. In this review, we will analyze some of the most important DNA and RNA viruses related to gestational infections.

Hybrid immunity in older adults is associated with reduced SARS-CoV-2 infections following BNT162b2 COVID-19 immunisation

BACKGROUND

Older adults, particularly in long-term care facilities (LTCF), remain at considerable risk from SARS-CoV-2. Data on the protective effect and mechanisms of hybrid immunity are skewed towards young adults precluding targeted vaccination strategies.

METHODS

A single-centre longitudinal seroprevalence vaccine response study was conducted with 280 LCTF participants (median 82 yrs, IQR 76-88 yrs; 95.4% male). Screening by SARS-CoV-2 polymerase chain reaction with weekly asymptomatic/symptomatic testing (March 2020-October 2021) and serology pre-/post-two-dose Pfizer-BioNTech BNT162b2 vaccination for (i) anti-nucleocapsid, (ii) quantified anti-receptor binding domain (RBD) antibodies at three time-intervals, (iii) pseudovirus neutralisation, and (iv) inhibition by anti-RBD competitive ELISA were conducted. Neutralisation activity: antibody titre relationship was assessed via beta linear-log regression and RBD antibody-binding inhibition: post-vaccine infection relationship by Wilcoxon rank sum test.

RESULTS

Here we show neutralising antibody titres are 9.2-fold (95% CI 5.8-14.5) higher associated with hybrid immunity (p < 0.00001); +7.5-fold (95% CI 4.6-12.1) with asymptomatic infection; +20.3-fold, 95% (CI 9.7-42.5) with symptomatic infection. A strong association is observed between antibody titre: neutralising activity (p < 0.00001) and rising anti-RBD antibody titre: RBD antibody-binding inhibition (p < 0.001), although 18/169 (10.7%) participants with high anti-RBD titre (>100BAU/ml), show inhibition <75%. Higher RBD antibody-binding inhibition values are associated with hybrid immunity and reduced likelihood of infection (p = 0.003).

CONCLUSIONS

Hybrid immunity in older adults was associated with considerably higher antibody titres, neutralisation and inhibition capacity. Instances of high anti-RBD titre with lower inhibition suggests antibody quantity and quality as independent potential correlates of protection, highlighting added value of measuring inhibition over antibody titre alone to inform vaccine strategy.

The quantity and quality of anti-SARS-CoV-2 antibodies show contrariwise association with COVID-19 severity: lessons learned from IgG avidity

Gaining more appreciation on the protective/damaging aspects of anti-SARS-CoV-2 immunity associated with disease severity is of great importance. This study aimed to evaluate the avidity of serum IgG antibodies against SARS-CoV-2 spike (S) and nucleocapsid (N) in hospitalized symptomatic COVID-19 patients and asymptomatic RT-PCR-confirmed SARS-CoV-2 carriers as well as to compare antibody avidities with respect to vaccination status, vaccination dose and reinfection status. Serum levels of anti-S and anti-N IgG were determined using specific ELISA kits. Antibody avidity was determined by urea dissociation assay and expressed as avidity index (AI) value. Despite higher IgG levels in the symptomatic group, AI values of both anti-S and anti-N IgG were significantly lower in this group compared to asymptomatic individuals. In both groups, anti-S AI values were elevated in one-dose and two-dose vaccinees versus unvaccinated subjects, although significant differences were only detected in the symptomatic group. However, anti-N avidity showed no significant difference between the vaccinated and unvaccinated subgroups. Almost all vaccinated patients of different subgroups (based on vaccine type) had higher anti-S IgG avidity, while the statistical significance was detected only between those receiving Sinopharm compared to the unvaccinated subgroup. Also, statistically significant differences in antibody AIs were only found between primarily infected individuals of the two groups. Our findings indicate a key role for anti-SARS-CoV-2 IgG avidity in protection from symptomatic COVID-19 and calls for the incorporation of antibody avidity measurement into the current diagnostic tests to predict effective immunity toward SARS-CoV-2 infection or even for prognostic purposes.

Diagnostic and Immunologic Testing for Varicella in the Era of High-Impact Varicella Vaccination: An Evolving Problem

The clinical presentation of varicella in unvaccinated persons, with skin vesicles and scabs, has facilitated the use of rapid diagnostic methods for confirming disease. Polymerase chain reaction (PCR) assays are the diagnostic method of choice. The sharp decline in unmodified cases of varicella due to the US varicella vaccination program has led to fewer healthcare providers being familiar with varicella presentation and an increased reliance on laboratory diagnosis to confirm suspected cases. The mild, atypical presentation of the disease in vaccinated persons (fewer skin lesions, mostly maculopapular) has made it more challenging for providers to recognize and also to collect samples to detect the virus. Nonetheless, PCR is highly sensitive and specific in confirming modified disease if adequate samples are provided. While a positive PCR result is confirmatory, interpreting a negative result can prove to be more challenging in determining whether suspected varicella is falsely negative or attributable to other causes. Enhanced education of healthcare providers is critical for adequate specimen collection from modified varicella cases. In addition, more sensitive commercial serologic assays are needed in the United States for varicella immunity testing in the vaccine era.

IgG Avidity Test as a Tool for Discrimination between Recent and Distant Toxoplasma gondii Infection—Current Status of Studies

Toxoplasma gondii, an obligate intracellular protozoan parasite, is the causative agent of one of the most prevalent zoonoses worldwide. T. gondii infection is extremely important from a medical point of view, especially for pregnant women, newborns with congenital infections, and immunocompromised individuals. Thus, an accurate and proper diagnosis of this infection is essential. Among the available diagnostic tests, serology is commonly used. However, traditional serological techniques have certain limitations in evaluating the duration of T. gondii infection, which is problematic, especially for pregnant women. Avidity of T. gondii-specific IgG antibodies seems to be a significant tool for discrimination between recent and distant infections. This article describes the problem of diagnosis of T. gondii infection, with regard to IgG avidity tests. The IgG avidity test is a useful serological indicator of toxoplasmosis, which in many cases can confirm or exclude the active form of the disease. IgG antibodies produced in the recent primary T. gondii infection are of low avidity while IgG antibodies with high avidity are detected in the chronic phase of infection. Furthermore, this paper presents important topics of current research that concern the usage of parasite recombinant antigens that may improve the performance of IgG avidity tests.

Implications derived from S-protein variants of SARS-CoV-2 from six continents

The spike (S) protein is a critical determinant of the infectivity and antigenicity of SARS-CoV-2. Several mutations in the S protein of SARS-CoV-2 have already been detected, and their effect in immune system evasion and enhanced transmission as a cause of increased morbidity and mortality are being investigated. From pathogenic and epidemiological perspectives, S proteins are of prime interest to researchers. This study focused on the unique variants of S proteins from six continents: Asia, Africa, Europe, Oceania, South America, and North America. In comparison to the other five continents, Africa had the highest percentage of unique S proteins (29.1%). The phylogenetic relationship implies that unique S proteins from North America are significantly different from those of the other five continents. They are most likely to spread to the other geographic locations through international travel or naturally by emerging mutations. It is suggested that restriction of international travel should be considered, and massive vaccination as an utmost measure to combat the spread of the COVID-19 pandemic. It is also further suggested that the efficacy of existing vaccines and future vaccine development must be reviewed with careful scrutiny, and if needed, further re-engineered based on requirements dictated by new emerging S protein variants.

Dynamics of IgG-avidity and antibody levels after Covid-19

BACKGROUND

A potentially important aspect of the humoral immune response to Covid-19 is avidity, the overall binding strength between antibody and antigen. As low avidity is associated with a risk of re- infection in several viral infections, avidity might be of value to predict risk for reinfection with covid-19.

OBJECTIVES

The purpose of this study was to describe the maturation of IgG avidity and the antibody-levels over time in patients with PCR-confirmed non-severe covid-19.

STUDY DESIGN

Prospective longitudinal cohort study including patients with RT-PCR confirmed covid-19. Blood samples were drawn 1, 3 and 6 months after infection. Antibody levels and IgG-avidity were analysed.

RESULTS

The majority had detectable s- and n-antibodies (88,1%, 89,1%, N = 75). The level of total n-antibodies significantly increased from 1 to 3 months (median value 28,3 vs 39,3 s/co, p<0.001) and significantly decreased from 3 to 6 months (median value 39,3 vs 17,1 s/co, p<0.001). A significant decrease in the IgG anti-spike levels (median value 37,6, 24,1 and 18,2 RU/ml, p<0.001) as well as a significant increase in the IgG-avidity index (median values 51,6, 66,0 and 71,0%, p<0.001) were seen from 1 to 3 to 6 months.

CONCLUSION

We found a significant ongoing increase in avidity maturation after Covid-19 whilst the levels of antibodies were declining, suggesting a possible aspect of long-term immunity.

Assessment of avidity related to IgG subclasses in SARS-CoV-2 Brazilian infected patients

SARS-CoV-2 is considered a global emergency, resulting in an exacerbated crisis in the health public in the world. Although there are advances in vaccine development, it is still limited for many countries. On the other hand, an immunological response that mediates protective immunity or indicates that predict disease outcome in SARS-CoV-2 infection remains undefined. This work aimed to assess the antibody levels, avidity, and subclasses of IgG to RBD protein, in symptomatic patients with severe and mild forms of COVID-19 in Brazil using an adapted in-house RBD-IgG ELISA. The RBD IgG-ELISA showed 100% of specificity and 94.3% of sensibility on detecting antibodies in the sera of hospitalized patients. Patients who presented severe COVID-19 had higher anti-RBD IgG levels compared to patients with mild disease. Additionally, most patients analyzed displayed low antibody avidity, with 64.4% of the samples of patients who recovered from the disease and 84.6% of those who died in this avidity range. Our data also reveals an increase of IgG1 and IgG3 levels since the 8th day after symptoms onset, while IgG4 levels maintained less detectable during the study period. Surprisingly, patients who died during 8-14 and 15-21 days also showed higher anti-RBD IgG4 levels in comparison with the recovered (P < 0.05), suggesting that some life-threatening patients can elicit IgG4 to RBD antibody response in the first weeks of symptoms onset. Our findings constitute the effort to clarify IgG antibodies' kinetics, avidity, and subclasses against SARS-CoV-2 RBD in symptomatic patients with COVID-19 in Brazil, highlighting the importance of IgG antibody avidity in association with IgG4 detection as tool laboratory in the follow-up of hospitalized patients with more significant potential for life-threatening.

The potential significance of high avidity immunoglobulin G (IgG) for protective immunity towards SARS-CoV-2

BACKGROUND

Avidity is defined as the strength of binding between immunoglobulin G (IgG) and its specific target epitope. IgG of high avidity is established during affinity maturation. Failure to achieve high avidity IgG may result in a lack of protective immunity towards infection and disease. It is known that the interaction between SARS-CoV-2 spike protein and its cellular receptor is driven by high affinity. Therefore, it is predictable that protective antibodies towards SARS-CoV-2 should show high affinity/avidity. AVIDITY AFTER SARS-COV-2 INFECTION: Recent findings by several groups demonstrate that the serological response towards infection with SARS-CoV-2 and seasonal coronaviruses is characterized by incomplete avidity maturation, followed by a decline of the serological response. This response might facilitate reinfection, prevent herd immunity and potentially allow repeated cycles of infection. CONSEQUENCES FOR VACCINATION TOWARDS SARS-COV-2: Therefore, the sole focus on antibody titers reached after vaccination towards SARS-CoV-2 might not be sufficient to evaluate the degree of achieved protection. Rather, it is suggested to include avidity determination to optimize vaccination protocols and achieve high avidity IgG directed towards SARS-CoV-2 through vaccination. Avidity determination might also be useful to control for truly protective immunity towards SARS-CoV-2 in individual cases.

The challenge of avidity determination in SARS-CoV-2 serology

The serological responses towards severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) nucleoprotein, receptor‐binding domain (RBD), and spike protein S1 are characterized by incomplete avidity maturation. Analysis with varying concentrations of urea allows to determine distinct differences in avidity maturation, though the total process remains at an unusually low level. Despite incomplete avidity maturation, this approach allows to define early and late stages of infection. It therefore can compensate for the recently described irregular kinetic patterns of immunoglobulin M and immunoglobulin G (IgG) directed towards SARS‐CoV‐2 antigens. The serological responses towards seasonal coronaviruses neither have a negative nor positive impact on SARS‐CoV‐2 serology in general. Avidity determination in combination with measurement of antibody titers and complexity of the immune response allows to clearly differentiate between IgG responses towards seasonal coronaviruses and SARS‐CoV‐2. Cross‐reactions seem to occur with very low probability. They can be recognized by their pattern of response and through differential treatment with urea. As high avidity has been shown to be essential in several virus systems for the protective effect of neutralizing antibodies, it should be clarified whether high avidity of IgG directed towards RBD indicates protective immunity. If this is the case, monitoring of avidity should be part of the optimization of vaccination programs.

Avidity maturation of immunoglobulin G (IgG) towards severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) antigens is distinct, but incomplete in most cases

Nevertheless, avidity determination allows to differentiate between acute and past SARS CoV‐infection

Avidity maturation is instrumental for differentiation between IgG responses towards SARS‐CoV‐2 and seasonal coronaviruses

It is suggested to clarify whether high avidity is required for and indicative of protective immunity.

The variability of the serological response to SARS-corona virus-2: Potential resolution of ambiguity through determination of avidity (functional affinity)

Data on the serological response toward severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) in 16 recent reports were analyzed and a high degree of variability was shown. Immunoglobulin M (IgM) responses were either found earlier than IgG, or together with IgG, later than IgG, or were missing. Therefore, clear distinctions between early, intermediate, and past infections are obviously not possible merely on the basis of IgM and IgG determinations. A review of publications on the serology of other virus groups shows that variable IgM responses can be found as well and therefore are not unique for SARS‐CoV‐2 infections. A model to explain this variability is proposed. The inclusion of avidity determination into regular diagnostic procedures has allowed to resolve such “atypical” serological constellations. The potential use of avidity determination for the diagnosis of COVID‐19, for risk assessment, epidemiological studies, analysis of cross reactions, as well as for the control of vaccination programs is suggested and discussed.

The serological response to SARS CoV‐2 infection is highly variable.

The mere detection of specific IgM and IgG does not allow to distinguish between acute and past infection.

The variable IgM and IgG responses after SARS CoV‐2 infection are analogous to serological findings in other virus systems.

Variable IgM and IgG responses can be rationally explained by models that describe immunoglobulin production by the immune system.

Avidity determination of SARS CoV‐2 IgG is suggested for resolution of diagnostic ambiguity.

Severe varicella-zoster virus pneumonia: a multicenter cohort study

BACKGROUND

Pneumonia is a dreaded complication of varicella-zoster virus (VZV) infection in adults; however, the data are limited. Our objective was to investigate the clinical features, management, and outcomes of critically ill patients with VZV-related community-acquired pneumonia (VZV-CAP).

METHODS

This was an observational study of patients with VZV-CAP admitted to 29 intensive care units (ICUs) from January 1996 to January 2015.

RESULTS

One hundred and two patients with VZV-CAP were included. Patients were young (age 39 years (interquartile range 32-51)) and 53 (52%) were immunocompromised. Time since respiratory symptom onset was 2 (1-3) days. There was a seasonal distribution of the disease, with more cases during spring and winter time. All but four patients presented with typical skin rash on ICU admission. Half the patients received mechanical ventilation within 1 (1-2) day following ICU admission (the ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO₂/FiO₂) = 150 (80-284), 80% with acute respiratory distress syndrome (ARDS)). Sequential Organ Failure Assessment (SOFA) score on day 1 (odds ratio (OR) 1.90 (1.33-2.70); p < 0.001), oxygen flow at ICU admission (OR 1.25 (1.08-1.45); p = 0.004), and early bacterial co-infection (OR 14.94 (2.00-111.8); p = 0.009) were independently associated with the need for mechanical ventilation. Duration of mechanical ventilation was 14 (7-21) days. ICU and hospital mortality rates were 17% and 24%, respectively. All patients were treated with aciclovir and 10 received adjunctive therapy with steroids. Compared to 60 matched steroid-free controls, patients treated with steroids had a longer mechanical ventilation duration, ICU length of stay, and a similar hospital mortality, but experienced more ICU-acquired infections.

CONCLUSIONS

Severe VZV-CAP is responsible for an acute pulmonary involvement associated with a significant morbidity and mortality. Steroid therapy did not influence mortality, but increased the risk of superinfection.

Microbiology laboratory and the management of mother-child varicella-zoster virus infection

Varicella-zoster virus, which is responsible for varicella (chickenpox) and herpes zoster (shingles), is ubiquitous and causes an acute infection among children, especially those aged less than six years. As 90% of adults have had varicella in childhood, it is unusual to encounter an infected pregnant woman but, if the disease does appear, it can lead to complications for both the mother and fetus or newborn. The major maternal complications include pneumonia, which can lead to death if not treated. If the virus passes to the fetus, congenital varicella syndrome, neonatal varicella (particularly serious if maternal rash appears in the days immediately before or after childbirth) or herpes zoster in the early years of life may occur depending on the time of infection. A Microbiology laboratory can help in the diagnosis and management of mother-child infection at four main times: (1) when a pregnant woman has been exposed to varicella or herpes zoster, a prompt search for specific antibodies can determine whether she is susceptible to, or protected against infection; (2) when a pregnant woman develops clinical symptoms consistent with varicella, the diagnosis is usually clinical, but a laboratory can be crucial if the symptoms are doubtful or otherwise unclear (atypical patterns in immunocompromised subjects, patients with post-vaccination varicella, or subjects who have received immunoglobulins), or if there is a need for a differential diagnosis between varicella and other types of dermatoses with vesicle formation; (3) when a prenatal diagnosis of uterine infection is required in order to detect cases of congenital varicella syndrome after the onset of varicella in the mother; and (4) when the baby is born and it is necessary to confirm a diagnosis of varicella (and its complications), make a differential diagnosis between varicella and other diseases with similar symptoms, or confirm a causal relationship between maternal varicella and malformations in a newborn.

Evaluation of potential immunogenicity differences between Pandemrix™ and Arepanrix™

In retrospective observational studies, an increased relative risk of incident narcolepsy was observed in some European countries among recipients of the AS03-adjuvanted, A(H1N1)pdm09, inactivated, detergent-split virion vaccine Pandemrix™ manufactured in Dresden, Germany (D-Pan H1N1). A similar increased risk was not observed in a retrospective population-based study in individuals in Quebec province, Canada, who received Aprepanrix™, a Quebec-manufactured AS03-adjuvanted A(H1N1)pdm09 inactivated, detergent-split virion vaccine (Q-Pan H1N1). Antibody responses in D-Pan versus Q-Pan vaccinees (adults/children) measured as hemagglutination inhibition (HI) titers 21 d post-vaccination were found to be equivalent (NCT01161160). The current post-hoc analysis was conducted to determine whether antibody avidity differed following immunization with the 2 vaccines. Using surface plasmon resonance, we evaluated the capacity of serum specimens (drawn from the comparative immunogenicity trial) from a subset of subjects aged 3-9 y who received either D-Pan or Q-Pan (N = 28/group), to bind to recombinant A(H1N1)pdm09 hemagglutinin. IgG antibodies were purified from Day 21 sera. Binding was assessed by end association level; dissociation by retention of antigen-antibody complexes at the end of the dissociation phase, and kd. Inter-run variability for the control monoclonal antibody, association levels and dissociation levels was low (CVs 1.3%, 7.8% and 1.4%, respectively); non-specific binding was negligible. High avidity and slow dissociation was observed for both groups (kd ≤ 10(-4)/s; geometric mean [IQR] association and dissociation levels for D-Pan/Q-Pan: 15.4 RU [13.4-17.7]/12.4 RU [10.8-14.3] and 94.5% [92.5-96.5]/95.5% [93.5-97.6], respectively). Association, but not dissociation levels correlated with HI titers. No significant differences in avidity parameters were observed between D-Pan and Q-Pan sera.

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

Alzheimer’s disease (AD) is a multifactorial disease with a still barely understood etiology. Herpes simplex virus 1 (HSV-1) has long been suspected to play a role in the pathogenesis of AD because of its neurotropism, high rate of infection in the general population, and life-long persistence in neuronal cells, particularly in the same brain regions that are usually altered in AD. The goal of this study was to evaluate HSV-1-specific humoral immune responses in patients with a diagnosis of either AD or amnestic mild cognitive impairment (aMCI), and to verify the possible relation between HSV-1-specific antibody (Ab) titers and cortical damage; results were compared to those obtained in a group of healthy controls (HC). HSV-1 serum IgG titers were measured in 225 subjects (83 AD, 68 aMCI, and 74 HC). HSV-specific Ab avidity and cortical gray matter volumes analyzed by magnetic resonance imaging (MRI) were evaluated as well in a subgroup of these individuals (44 AD, 23 aMCI, and 26 HC). Results showed that, whereas HSV-1 seroprevalence and IgG avidity were comparable in the three groups, increased Ab titers (p < 0.001) were detected in AD and aMCI compared to HC. Positive significant correlations were detected in AD patients alone between HSV-1 IgG titers and cortical volumes in orbitofrontal (region of interest, ROI1 R_Sp0.56; p = 0.0001) and bilateral temporal cortices (ROI2 R_Sp0.57; p < 0.0001; ROI3 R_Sp0.48; p = 0.001); no correlations could be detected between IgG avidity and MRI parameters. Results herein suggest that a strong HSV-1-specific humoral response could be protective toward AD-associated cortical damage.

Pathogenesis and current approaches to control of varicella-zoster virus infections

Varicella-zoster virus (VZV) was once thought to be a fairly innocuous pathogen. That view is no longer tenable. The morbidity and mortality due to the primary and secondary diseases that VZV causes, varicella and herpes zoster (HZ), are significant. Fortunately, modern advances, including an available vaccine to prevent varicella, a therapeutic vaccine to diminish the incidence and ameliorate sequelae of HZ, effective antiviral drugs, a better understanding of VZV pathogenesis, and advances in diagnostic virology have made it possible to control VZV in the United States. Occult forms of VZV-induced disease have been recognized, including zoster sine herpete and enteric zoster, which have expanded the field. Future progress should include development of more effective vaccines to prevent HZ and a more complete understanding of the consequences of VZV latency in the enteric nervous system.

Use of an anti-hepatitis C virus (HCV) IgG avidity assay to identify recent HCV infection

There is no reliable and simple diagnostic marker available to diagnose recent hepatitis C virus (HCV) infection. It has been shown that the avidity of specific IgG antibody is low in primary viral infection and increases with time. We report the development of an anti-HCV avidity assay derived from a commercially available test. A panel of 117 sera was first examined for IgG avidity. It was composed of samples from patients with recent (group 1, n = 14), chronic (group 2, n = 70), and resolved (group 3, n = 33) HCV infections. Avidity index (AI) values observed in recently infected patients were significantly lower (12.0% +/- 9.2% [mean +/- standard deviation]) than those found in chronic carriers (83.1% +/- 15.2%). Using a threshold of 43.0%, this assay distinguished between groups 1 and 2 with very high sensitivity (98%) and specificity (100%). For group 3, a broader distribution of the AI values was observed (54.8% +/- 27.3%), suggesting that this index would not be useful in HCV RNA-negative patients. Blind validation of the test was carried out with a panel of 36 serum samples from 17 HCV seroconverters. The assay described here is a useful tool to distinguish recent from chronic infection in HCV-viremic patients.

Herpes zoster in healthy infants and toddlers after perinatal exposure to varicella-zoster virus: a case series and review of the literature

Exposure to varicella-zoster virus in utero or during the first months of life is the main risk factor for the development of herpes zoster (HZ) in healthy children. We report a case series of 16 infants and toddlers who presented with HZ after early exposure to varicella-zoster virus. Two patients had recurrences. Despite the severity of the rash in some cases, the benign course and the long-term good prognosis of HZ in healthy children is noteworthy.

Bilateral middle cerebral artery infarctions following mild varicella infection: a case report

We report a two-year and one-month-old immunocompetent boy who developed aphasia and right hemiparesis eight months after mild varicella with only a few vesicles. Magnetic resonance images and angiography demonstrated mixed acute and old infarctions of the bilateral middle cerebral arteries. VZV-DNA was detected on polymerase chain reaction analysis of cerebral spinal fluid (CSF). He was treated with intravenous acyclovir and edaravone, and his speech and motor functions had almost recovered after two months. Cerebral lesions of the bilateral middle cerebral artery territories and virus DNA detection from CSF are rare in VZV-related vasculopathy and suggest incomplete immunoresponse to varicella in this patient.

Varicella

Varicella-zoster virus, a herpesvirus, causes varicella (chickenpox) and, after endogenous reactivation, herpes zoster (shingles). Varicella, which is recognised by a characteristic vesicular rash, arises mainly in young children, although older individuals can be affected. In immunocompetent patients, symptoms are usually mild to moderate, but an uncomplicated severe case can have more than 1000 lesions and severe constitutional symptoms. Serious complications--including central nervous system involvement, pneumonia, secondary bacterial infections, and death--are sometimes seen. Varicella can be prevented by vaccination. Vaccine is about 80-85% effective against all disease and highly (more than 95%) effective in prevention of severe disease. In the USA, a routine childhood immunisation programme has reduced disease incidence, complications, hospital admissions, and deaths in children and in the general population, indicating strong herd immunity. Similar immunisation programmes have been adopted by some other countries, including Uruguay, Germany, Taiwan, Canada, and Australia, and are expected to be implemented more widely in future.

Serum antibody responses in children with rotavirus diarrhea can serve as proxy for protection

We examined sera from 42 patients 1 to 30 months of age for rotavirus immunoglobulin M (IgM), IgA, IgG, and IgG subclasses and sought to determine if serum antibody could serve as a reliable marker for prediction of disease severity. Infants in the first few months of life usually had high maternal IgG titers and, when they were infected with rotavirus, had low IgM titers or no IgM in acute-phase sera and poor seroconversions 3 weeks later, suggesting that maternal antibodies had inhibited viral replication and antibody responses. All patients > or =6 months of age had IgM in acute-phase sera, indicating that IgM is a good marker for acute rotavirus infection. IgG was the best overall predictor of an infection, as the convalescent-phase sera of 81% of the patients had a fourfold rise in the IgG titer. IgA titers in convalescent-phase sera and conversion rates were higher among patients > or =12 months of age than among children younger than 12 months. IgG1 was the predominant subclass detected in the acute-phase sera of some children and in all 28 convalescent-phase serum samples examined. Patients with preexisting acute-phase IgG titers of > or =100 or > or =200 had diarrhea that was less severe or of a shorter duration. These results indicate that serum IgG is the most reliable marker for seroconversion and is a consistent proxy for protection against severe disease.

Usefulness of specific IgG avidity for diagnosis of hepatitis A infection

AIM

Diagnosis of acute hepatitis A virus (HAV) infection is classically based on the detection of HAV-IgM. Nevertheless, HAV-IgM can be positive for patients with polyclonal stimulation of their immune system (i.e. immune reactivation). To improve the diagnostic yield, an avidity test for HAV-IgG antibodies was developed and tested.

METHODS

Avidity tests were performed in 128 sera: 11 selected samples from patients with past infection, 15 acute hepatitis A, 10 vaccinated subjects and 4 patients with immune reactivation as well as 84 HAV-IgM positive unselected sera, provided by routine laboratories.

RESULTS

Patients with past infection had avidities over 70%, whereas avidities in patients with acute hepatitis A were below 50% during the first month following the onset of symptoms. As expected, patients with immune reactivation had avidities over 70% consistent with past infection. The results obtained for the 84 unselected sera allowed reconsidering the diagnosis of acute hepatitis A for nearly a third of patients.

CONCLUSION

This test could improve the diagnosis of acute hepatitis A infection, particularly in elderly patients.

Diagnostic relevance of immunoglobulin G avidity for hepatitis A virus

Diagnosis of acute hepatitis A virus (HAV) infection is based on the detection of HAV immunoglobulin M (IgM). However, IgM could be detected due to nonspecific polyclonal activation of the immune system. An avidity test for anti-HAV IgG was developed to distinguish acute infection, where low-avidity antibodies are detected, from immune reactivation. The assay was tested on 104 samples, including 11 sera from patients with past infection, 15 sera from patients with acute infection and 4 collected after recovery, 10 sera from vaccinated subjects, 4 sera from patients with suspected immune reactivation, and 60 unselected HAV-IgM positive sera, collected over 1 year in a routine laboratory. The avidity index (AI) was expressed as percentage. The results were provided as the mean +/- one standard deviation. Patients with a history of prior infection had AIs of >70% (mean, 86% +/- 10), whereas the mean AI was 36% +/- 16 during acute HAV infection (P < 0.001). Within the first month after the onset of hepatitis, avidity was either noncalculable due to a very low IgG titer or <50%. In patients with immune reactivation, avidity was >70% (88% +/- 10%), a finding consistent with a prior infection. Among the 60 unselected sera, 35 (58%) had a noncalculable or <50% avidity, and most of them had a detectable HAV RNA, confirming HAV infection. In contrast, 16 (27%) had an avidity of >70%, and none was reverse transcription-PCR positive, suggesting immune reactivation. These 16 patients were significantly older than the others (50 +/- 16 years versus 26 +/- 14 years). The new anti-HAV IgG avidity assay we developed could improve HAV infection diagnosis, particularly in elderly patients.

A serological testing algorithm for the diagnosis of primary CMV infection in pregnant women

OBJECTIVES

Serological diagnosis of CMV primary infection is usually based on the detection of specific IgM antibody. However, as the presence of IgM antibody is not always correlated with primary infection, measurement of IgG avidity must be performed. The aim of our study was to evaluate the best procedure for serological diagnosis of CMV primary infection. In other words, is it better to first search for IgM antibody, and, if positive, then measure IgG avidity, or first measure IgG avidity without the detection of IgM antibody?

MATERIALS

CMV-IgM detection and CMV-IgG avidity measurement were performed on 310 IgG positive sera from pregnant women.

RESULTS

CMV-IgM antibody was detected positive for 9 of 310 sera. Using CMV-IgG avidity index (AI), dating of infection was difficult in 81/310 cases (26%), while it failed in only 3/310 cases using CMV-IgM plus CMV-IgG AI.

CONCLUSION

The diagnosis of primary CMV infection can be based on the detection of CMV-IgM antibody first and then on the measurement of CMV-IgG AI.

Development and use of a type-specific antibody avidity test based on herpes simplex virus type 2 glycoprotein G

OBJECTIVES

It is difficult to discriminate between lesions resulting from recently acquired versus established genital herpes simplex virus type 2 (HSV-2) infection. Methods not based on history or serum IgM status are needed.

GOAL

Our goal was to use type-specific gG-2 antibody avidity determinations based on HerpeSelect HSV-2 enzyme-linked immunosorbent assay (ELISA) to identify new infections.

STUDY

Sera (N = 168) from 71 patients with first-episode genital herpes and 45 sera from 21 patients with recurrent episodes were tested.

RESULTS

Median avidity increased from 30.2 in sera drawn </=6 weeks to 54.9 >6 weeks after infection (P <0.001). Patients with recurrent episodes and established HSV-2 infections (median, 6.1 years' duration) had higher avidity antibodies (median, 92.7; range, 55.1-100) than patients after first episodes (median, 33.7; range, 6.4-73.9; P <0.001).

CONCLUSION

Avidity testing based on HerpeSelect ELISA could be a cost-effective method to identify patients with new HSV-2 infections.

A new method for determination of varicella-zoster virus immunoglobulin G avidity in serum and cerebrospinal fluid

Background

Avidity determination of antigen-specific immunoglobulin G (IgG) antibodies is an established serological method to differentiate acute from past infections. In order to compare the avidity of varicella-zoster virus (VZV) IgG in pairs of serum and cerebrospinal fluid (CSF) samples, we developed a new technique of avidity testing, the results of which are not influenced by the concentration of specific IgG.

Methods

The modifications introduced for the new VZV IgG avidity method included the use of urea hydrogen peroxide as denaturing reagent, the adaptation of the assay parameters in order to increase the sensitivity for the detection of low-level VZV IgG in CSF, and the use of a new calculation method for avidity results. The calculation method is based on the observation that the relationship between the absorbance values of the enzyme immunoassays with and without denaturing washing step is linear. From this relationship, a virtual absorbance ratio can be calculated. To evaluate the new method, a panel of serum samples from patients with acute and past VZV infection was tested as well as pairs of serum and CSF.

Results

For the serum panel, avidity determination with the modified assay gave results comparable to standard avidity methods. Based on the coefficient of variation, the new calculation method was superior to established methods of avidity calculation.

Conclusions

The new avidity method permits a meaningful comparison of VZV IgG avidity in serum and CSF and should be of general applicability for easy determination of avidity results, which are not affected by the concentration of specific IgG.

Immunoglobulin G antibody avidity assay for serodiagnosis of hepatitis C virus infection

It has been reported that the avidity of specific IgG antibody is lower in primary viral infection than in chronic viral infection. However, few studies have been reported on the IgG avidity in hepatitis C virus (HCV) infection. In the present study, 36 patients with antibody to HCV (anti-HCV) were examined for IgG avidity by an enzyme immunoassay with or without urea elution. The avidity index was significantly low in patients with primary HCV infection (7.7 +/- 6.8%, mean +/- SD), compared with patients with chronic HCV infection (77.0 +/- 21.8%) and individuals with past HCV infection (44.5 +/- 12.6%). Temporal changes of IgG avidity were examined in six patients with primary HCV infection. The avidity index was low in the acute phase of the infection and then increased with time. These results suggest that the avidity assay for IgG anti-HCV is a useful method for distinguishing primary HCV infection from chronic or past HCV infection.

Expression of neutralizing recombinant human antibodies against Varicella Zoster virus for use as a potential prophylactic

Chickenpox is a highly infectious disease that can be life-threatening to certain groups such as the newborn of nonimmune mothers and immunocompromised patients. At present, prophylactic treatment of individuals at risk involves the use of a polyclonal antibody preparation derived from the pooled sera of hyperimmune donors. While this product is effective, there are problems associated with maintaining supply, which depends on the availability of donors, and the variation of potency between batches. An effective human monoclonal preparation would be of value by providing a well-characterized and standardized preparation available on demand. In this study recombinant human anti-varicella zoster virus (VZV) monoclonals were generated from the mRNA of unstable anti-VZV secreting heterohybridoma cell lines, and characterized according to their molecular weight, isoelectric point, glycosylation, binding to C1q, and efficacy at neutralizing VZV in vitro. In one antibody (AEVZ 5.3) the VH region was grafted from the IgG1 parent antibody onto an IgG3 backbone to determine the effect of isotype on neutralization in vitro. Antibodies were expressed from NSO cells at concentrations of 3-24 microg/mL and contained the expected heavy and light chain fragments and N-linked glycan structures. Both AEVZ 5.1 and AVEZ 4 antibodies were IgG1 and recognized the viral coat protein glycoprotein E; both showed complement-independent and complement-enhanced neutralization. Changing the isotype of AEVZ 5.1 from IgG1 to IgG3 (AEVZ 5.3) further enhanced VZV neutralization in the presence of complement, but reduced its neutralization capacity in the absence of complement. Complement enhancement was consistent with our findings that the IgG3 form could bind more molecules of C1q. The results demonstrate the successful use of recombinant methods to generate stable, functional monoclonal antibodies. Modifications of the original antibodies were made with the aim of improving functionality. The resulting cell lines could be used for large-scale production of well-characterized antibodies for therapeutic use.

Predictive value of maternal-IgG avidity for congenital human cytomegalovirus infection

BACKGROUND

Human cytomegalovirus (HCMV) is now the most common cause of viral intrauterine infection. Fetal damage is mostly linked to maternal primary infection. It is therefore important to differentiate primary from recurrent or persistent HCMV infection in pregnant females. For this purpose, IgM tests are not reliable enough and the measurement of the IgG avidity appears to be presently the best method.

OBJECTIVE

To evaluate the performance of the measurement of HCMV-IgG avidity by a 8 M urea denaturation assay in predicting congenital infection in the offspring.

STUDY DESIGN

Seventy-eight women were included in this study on the basis of a HCMV IgM positive or equivocal result on a first serum during pregnancy, but without a documented seroconversion history. The IgG avidity was measured and correlated with the outcome of the pregnancy.

RESULTS

In eight cases of HCMV in utero infection the maternal HCMV-IgG avidity index was below 50%. One case of HCMV in utero infection was observed despite a high avidity index during the second trimester of the pregnancy. High or intermediate HCMV-IgG avidity indexes during the first trimester of pregnancy were not associated with a congenital infection.

CONCLUSIONS

Even in the presence of an IgM positive result, an HCMV IgG avidity index above 65% on a serum obtained during the first trimester of pregnancy could reasonably be considered as a good indicator of past HCMV infection. In these conditions invasive prenatal diagnosis is not necessary.

B-cell epitopes of varicella-zoster virus glycoprotein II

B-cell epitopes of varicella-zoster virus glycoprotein II were mapped by means of solid phase ELISA, synthetic oligopeptides (constructed according to the Davison-Scott sequencing of the varicella-zoster virus genome) and sera from varicellae and herpes zoster patients. The individual pattern of antibody peptide binding varied considerably but at least 9 more reactive sites seemed discernible. A 31-mer-peptide corresponding to a hydrophilic segment of the glycoprotein (aa 417-447) was constructed. This peptide reacted with 2 out of 4 varicellae and 5 out of 9 zoster sera, respectively.

Avidity of IgG antibodies distinguishes primary from non-primary cytomegalovirus infection in pregnant women

BACKGROUND

Human cytomegalovirus (HCMV) is the most common cause of viral intrauterine infection. Fetal damage is mostly linked to maternal primary infection. It is therefore important to differentiate primary from non-primary infection in pregnant females. IgM tests often used for this purpose are not reliable enough.

OBJECTIVE

To evaluate an HCMV-IgG urea-elution assay for its ability to distinguish primary from non-primary infection. In this assay, soaking the antigen-antibody complex with an urea containing solution frees antibodies with low avidity but has no influence on those with high avidity. An avidity index (AI) was calculated: AI = (OD with urea/OD without urea) x 100.

STUDY DESIGN

HCMV-IgG avidity was measured on a single serum of 79 patients with past infection (pregnant women, graft recipients and blood donors) and of 63 patients (78 sera) with documented seroconversion (pregnant women and graft recipients). Sixty-one pregnant women positive or equivocal for HCMV-IgM but without a documented seroconversion were included in this study.

RESULTS

Most (72/79) of the patients with past infection had an AI > 65% and all but one had an AI > 50%. In pregnant women, in the case of a primary infection within the past 3 months, AI are usually (51/53) < 50% and never > 65%. Among the IgM positive pregnant women who lack a seroconversion history, 38 had AI > 65% suggestive of an infection that had occurred at least 3 months earlier, 11 had an AI in a grey area between 50 and 65% and 12 had an AI < 50%, suggestive of a recent primary infection.

CONCLUSIONS

In pregnant women, measurement of the IgG avidity may help to date a HCMV infection, an AI > 65% highly suggests a past infection while an AI < 50% corresponds to a recent primary infection.

Measles virus-specific immunoglobulin G subclass response in serum and cerebrospinal fluid

BACKGROUND

While many previous studies have focused on the impairment in the cellular immunity during measles virus infection, to date, a limited amount of data is available concerning the virus-specific IgG subclass response during measles virus infection.

OBJECTIVE

The purpose of this study is to analyze the measles virus infection on the basis of virus-specific IgG subclass (G 1 and G 3).

STUDY DESIGN

Frozen-stored, serum and/or cerebospinal fluid samples from three groups of patients were tested retrospectively; Group 1 comprised 14 patients with measles primary infection, group 2, ten patients with reinfection/vaccine failure, and group 3, seven patients with subacute sclerosing panencephalitis. The method used was a modified ELISA method utilizing the Enzygnost IgG detection kit with mouse-monoclonal antibodies (clone HP6091 for IgG 1 and clone HP6050 for IgG 3). Avidity testing for each subclass IgG was also performed for selected samples by means of an 8 M urea-denaturation method.

RESULTS

In group 1, the IgG 3 could be detected in serum within 7 days from the onset of rash more frequently than IgG 1. In the cases of group 2, both subclasses were detected in very acute phase serum samples. In these cases, the IgG 1-specific avidity was always higher than that of IgG 3. In group 3, the subclass IgGs detected in the cerebrospinal fluid had a lower avidity than those in the serum.

CONCLUSIONS

Our results suggested that in measles virus infection, like other viral infections, the IgG 3 response normally occurs before the IgG 1 response, and plays a major role in the acute phase immunity during the primary infection, while the IgG 1 plays a major role in the maintenance of immunity. Continuously produced IgG 1 and IgG 3 in the central nervous system in cases of subacute sclerosing panencephalitis may be derived from cell populations different from those in the blood.

Evolution of envelope-specific antibody responses in monkeys experimentally infected or immunized with simian immunodeficiency virus and its association with the development of protective immunity

Previous studies of attenuated simian immunodeficiency virus (SIV) vaccines in rhesus macaques have demonstrated the development of broad protection against experimental challenge, indicating the potential for the production of highly effective immune responses to SIV antigens. However, the development of this protective immune status was found to be critically dependent on the length of time postvaccination with the attenuated virus strain, suggesting a necessary maturation of immune responses. In this study, the evolution of SIV envelope-specific antibodies in monkeys experimentally infected with various attenuated strains of SIV was characterized by using a comprehensive panel of serological assays to assess the progression of antibodies in longitudinal serum samples that indicate the development of protective immunity. In parallel studies, we also used the same panel of antibody assays to characterize the properties of SIV envelope-specific antibodies elicited by inactivated whole-virus and envelope subunit vaccines previously reported to be ineffective in producing protective immunity. The results of these studies demonstrate that the evolution of protective immunity in monkeys inoculated with attenuated strains of SIV is associated with a complex and lengthy maturation of antibody responses over the first 6 to 8 months postinoculation, as reflected in progressive changes in antibody conformational dependence and avidity properties. The establishment of long-term protective immunity at this time in general parallels the absence of further detectable changes in antibody responses and a maintenance of relatively constant antibody titer, avidity, conformational dependence, and the presence of neutralizing antibody for at least 2 years postinoculation. In contrast to the mature antibody responses elicited by the attenuated SIV vaccines, the whole-virus and envelope subunit vaccines in general elicited only immature antibody responses characterized by poor reactivity with native envelope proteins, low avidity, low conformational dependence, and the absence of neutralization activity against the challenge strain. Thus, these studies establish for the first time an association between the effectiveness of experimental vaccines and the capacity of the vaccine to produce a mature antibody response to SIV envelope proteins and further indicate that a combination of several antibody parameters (including titer, avidity, conformational dependence, and virus neutralization) are superior to any single antibody parameter as prognostic indicators to evaluate candidate AIDS vaccines.

Differentiation of primary from nonprimary genital herpes infections by a herpes simplex virus-specific immunoglobulin G avidity assay

An immunoglobulin G (IgG) antibody avidity assay which uses protein-denaturing agents and a modification of an enzyme-linked immunosorbent assay have been investigated for their usefulness in distinguishing primary genital herpes simplex virus (HSV) infections from nonprimary infections. Forty-nine serum specimens from patients with primary, recurrent, and nonprimary first-episode genital herpes were studied. The clearest separation was obtained with 6 M urea treatment, giving mean avidity indices of 0.398 for sera < or = 100 days after the infection and 0.879 for sera > 100 days after the infection (P < 0.001). No significant difference in avidity indices was observed between the recurrent and nonprimary first-episode infections. Determination of the avidity of HSV-specific IgG will improve the diagnostic potential of HSV serology.

Enzyme-linked immunosorbent assay-IgG antibody avidity test for single sample serologic evaluation of measles vaccines

A measles-specific enzyme-linked immunosorbent assay (ELISA)-IgG avidity test for serologic evaluation of the efficacy of measles vaccines with only one blood sample was evaluated after vaccination with three measles vaccine strains. Avidity indices were determined by the urea elution technique in samples presenting antibody titers > or = 100 mIU/ml. All 127 sera collected 2-8 weeks after primary vaccination with Biken-CAM70 measles vaccine had low avidity indices (LAI, when < or = 29%) with a time-dependent increase in avidity. In samples collected 6-10 weeks after vaccination with Edmonston-Zagreb, LAI were also observed in all 31 sera tested (mean = 15%) and in 233/242 (96.3%) filter paper samples from primary vaccination with Schwarz vaccine (mean = 14%). There was no difference in the mean avidity among the three groups of primary vaccinees, although the Schwarz group had higher antibody titers. In contrast, only 1/36 (2.8%) serum samples from children who were seropositive at the time of measles vaccination had LAI (mean = 56%), despite the fact that they were collected early (2-5 weeks after vaccination). Of 90 serum samples from children vaccinated in the past with two doses and of 42 cord blood serum samples, none had LAI. It is concluded that this test is a good tool for evaluating serologically the efficacy of a single dose schedule of measles vaccine. With only one postvaccination sample, the test can discriminate nonresponders (antibody titers below 100 mIU/ml), primary responders (antibody titers > or = 100 mIu/ml with LAI), and those previously immunized (antibody titers > or = 100 mIU/ml with high avidity indices). The seroconversion rate can be calculated after excluding the latter.

Humoral immunity in DiGeorge syndrome

OBJECTIVE

To assess humoral immunity after immunization and natural infection in patients with clinical manifestations of the DiGeorge anomalad.

DESIGN

Retrospective review of cases.

SETTING

Ambulatory immunology clinic of a tertiary care teaching hospital.

PATIENTS

The 13 patients had a symptom complex including congenital heart disease, characteristic facies of the DiGeorge anomalad, possible hypocalcemia, and thymic hypoplasia or aplasia. Molecular and cytogenic studies of 12 patients demonstrated that all had 22q11 microdeletions.

METHODS

Serial studies included lymphocyte population enumeration by flow cytometry, lymphocyte proliferation assays with the mitogens phytohemagglutinin and pokeweed mitogen and Staphylococcus aureus, and immunoglobulin quantitation. Specific antibody studies included virus neutralization assays for poliovirus antibodies, and enzyme-linked immunosorbent assay for diphtheria, tetanus, measles, rubella, varicella-zoster virus (VZV), and cytomegalovirus (CMV) antibodies. Avidity of rubella, VZV, and CMV antibodies was tested by enzyme-linked immunosorbent assay modified to include a mild protein denaturant in the first wash after incubation with sera.

RESULTS

All patients had a CD3+ cell count greater than 0.500 x 10(9)/L and a CD4+ cell count greater than 0.350 x 10(9)/L). One patient had low proliferation responses to S. aureus, and one to phytohemagglutinin and pokeweed mitogen. Immunoglobulin levels, compared with those in age-related control subjects, were normal except that two patients had transient, borderline low IgG levels and two had elevated IgA levels. Specific antibody tests showed (No. of patients with positive results/No. tested) the following: diphtheria (13/13); tetanus (13/13); poliomyelitis caused by polio virus type 1 (5/9), type 2 (9/9), and type 3 (8/9); measles (11/13); rubella (11/13); and infection with VZV (5/5) and CMV (7/13). There were no significant differences in antibody avidity results between patients and control subjects for rubella (mean avidity index, 83.5 +/- 8.79 vs 85 +/- 17.6), VZV (81.6 +/- 3.98 vs 65.1 +/- 12.38), or CMV (69.3 +/- 22.31 vs 73.3 +/- 12.46).

CONCLUSIONS

Patients with "partial" DiGeorge anomalad, defined by clinical and immunologic criteria, can be immunized and for the most part can generate good antibody responses.

Application of fluoroimmunoassay to the identification of low avidity specific IgG against pathogenic human viruses and Toxoplasma gondii

BACKGROUND

Serological diagnosis of primary viral infections is usually made by detection of specific IgM. In some cases, false positive results (mainly due to crossreactions between closely related viruses) can be obtained. Moreover, some primary infections occur without specific IgM response. Thus, alternative serological approaches are required for diagnosis. Detection of low avidity, specific IgG has been applied as a useful serological marker for diagnosing infections caused by several viruses and Toxoplasma gondii.

OBJECTIVE

The standardization and application of specific IgG avidity assays using a semiautomated solid phase immunoassay (fluoroimmunoassay (FIA)) on the basis of the urea elution principle, for the characterization of low avidity specific IgG against rubella virus, herpes simplex virus (HSV), varicella-zoster virus (VZV), cytomegalovirus (CMV) and T. gondii.

STUDY DESIGN

The method consists of two simultaneous determinations, one as recommended by the manufacturer and the other including a washing step with 8 M urea after the antigen-antibody reaction. A reduction in titer higher than, or equal to, 50% was considered indicative for presence of low avidity specific IgG.

RESULTS

When applied to the diagnosis of infections, this method showed sensitivity ranging from 81% to 100%, and absolute specificity. The detection of low avidity specific IgG allowed the differentiation between primary and recurrent infections caused by VZV. Furthermore, it helped in the identification of CMV as the etiological agent of congenital infection in the absence of specific IgM response, as well as in the elucidation of crossreactivity between antigenically related viruses, i.e., VZV and HSV, and Epstein-Barr virus and CMV.

CONCLUSION

FIA can be used for the characterization of the avidity of specific IgG antibody as a diagnostic test in clinical laboratories.