Comparison of the Raji cell line fluorescent antibody to membrane antigen test and the enzyme-linked immunosorbent assay for determination of immunity to varicella-zoster virus

Evaluation of flow cytometry-based fluorescent antibody to membrane antigen test to measure the humoral immunity against the varicella-zoster virus

The fluorescent antibody to membrane antigen (FAMA) test is the gold standard for measuring the immunity induced by varicella vaccines with high sensitivity and specificity. However, certain aspects of the FAMA test, such as time consumption, non-automation, and subjective interpretation by observers using fluorescence microscopy, are obstacles to handling large amounts of samples. To overcome these hurdles, flow cytometry was adopted to analyze and compare the flow FAMA titer with the classic FAMA titer. In addition, to save time in FAMA antigen preparation and reduce lot-to-lot variation, the stability of the FAMA antigen stored in liquid nitrogen was investigated. The FAMA test was performed on sera from 229 children, and antibody titers were analyzed using fluorescence microscopy (classic FAMA) and flow cytometry (flow FAMA). For comparison, glycoprotein enzyme immunoassay (gpEIA) titer was also measured. A strong correlation was found between the flow and classic FAMA titers, and the flow FAMA and gpEIA titers, with Pearson's r of 0.9316 and 0.8588, respectively. Between the classic FAMA and gpEIA titers, the Pearson's r value was 0.8156. The positive percent agreement, negative percent agreement, and area under the curve of the flow FAMA against classic FAMA were 95.0 %, 86.8 %, and 0.909, respectively. And those of the flow FAMA against gpEIA were 80.0 %, 87.6 %, and 0.838, respectively. The FAMA antigen stored in liquid nitrogen was stable for up to 12 months. Based on the above data, flow FAMA has the potential to be used as an alternative to classic FAMA. Moreover, pre-made FAMA antigen may reduce the preparation time and lot-to-lot variation of FAMA test.

Current Methods for the Detection of Antibodies of Varicella-Zoster Virus: A Review

Infection with the varicella-zoster virus (VZV) causes chickenpox and shingles, which lead to significant morbidity and mortality globally. The detection of serum VZV-specific antibodies is important for the clinical diagnosis and sero-epidemiological research of VZV infection, and for assessing the effect of VZV vaccine immunization. Over recent decades, a variety of methods for VZV antibody detection have been developed. This review summarizes and compares the current methods for detecting VZV antibodies, and discussed future directions for this field.

Enhanced Potency and Persistence of Immunity to Varicella-Zoster Virus Glycoprotein E in Mice by Addition of a Novel BC02 Compound Adjuvant

Herpes zoster (HZ) is one of two distinct syndromes caused by Varicella-zoster virus (VZV). A primary infection with VZV causes varicella in susceptible young children. After resolution of the primary infection, VZV establishes a lifelong latency within the cranial or dorsal root ganglia. With increasing age, family history of shingles, immunosuppression or other risk factors, there is a decline in the virus-specific T-cell-mediated immune (CMI) response which allows reactivation of latent VZV in the root ganglia resulting in HZ. There are currently two vaccines that have been approved to prevent HZ and postherpetic neuralgia (PHN) but one is a live attenuated vaccine, the protective effect of which is considered to decrease significantly with the age of the recipient. However, a recombinant subunit vaccine may provide targeted VZV-specific cellular and humoral immunity, giving it a more potent and longer-lasting protective effect against HZ. The current study reports the development of a novel adjuvant, BC02 (BCG CpG DNA compound adjuvants system 02), composed of Al(OH)₃ inorganic salt adjuvant and BC01 (BCG CpG DNA compound adjuvants system 01), a Toll-like receptor 9 (TLR9) agonist. Immunogenicity and compatibility with recombinant VZV glycoprotein E (gE) in mice were studied. The BC02-adjuvanted gE experimental vaccine was highly effective in eliciting both humoral and cellular immune responses to the recombinant gE glycoprotein and VZV-Oka in a mouse model. The efficient production and long-term persistence of gE and VZV-Oka-specific IFN-γ, IL-2-specific T cells and memory B cells in the early (1W), middle (7W), middle-late (15W), and final (27W) immune stages were established. Results of fluorescent antibody to membrane antigen (FAMA) and serum antibody plaque reduction tests also showed that the BC02 adjuvanted-gE experimental vaccine induced mice to secrete neutralizing antibodies against clinically isolated VZV strains. In combination, the current data suggest that the BC02 compound adjuvant offers a strategy to induce an appropriately strong cellular and humoral immunity against the VZV gE protein subunit to improve vaccine efficacy.

Varicella susceptibility in a Canadian population

OBJECTIVE

To determine susceptibility to varicella zoster virus (VZV) infection among children, pregnant women and health care workers in Newfoundland.

DESIGN

Cohort and cross-sectional, province-wide, population-based seroprevalence study.

STUDY POPULATION AND METHODS

A cohort of 586 children aged one year, a cross-sectional group of 1135 school children aged five to 15 years, 3643 pregnant women aged 15 to 45 years, and 5386 persons in health care settings aged 15 to 55 years. Susceptibility to varicella was determined by enzyme immunoassay based on serum antibody to VZV.

RESULTS

Among the cohort of 586 children, 565 (96.4%) did not have detectable VZV antibody at one year of age. The proportion with VZV antibody increased thereafter to 12.8% and 33.9%, respectively, at age two and four years, indicating the extent of exposure to VZV at these ages. Among the 1135 school-age children, the proportion testing positive for VZV antibody increased from 44% at five years of age to 88.9% at 15 years of age, indicating the cumulative incidence of varicella in this age group. Among pregnant women, 92.1% tested positive for VZV antibody, and the corresponding figure for the health care group was 93.1%. In both groups, the proportion testing positive for VZV antibody increased with advancing age, from 89.6% for the 15- to 19-year age group to 96.5% for those over the age of 40 years.

CONCLUSIONS

The risk of VZV infection increases steadily from one year of age, reaching a peak during school years. The study data support the recent Canadian recommendation to vaccinate any person older than 12 months of age who is susceptible to VZV. Among the adult population, the proportion susceptible will be under 10% for the foreseeable future, and for those at risk, selective vaccination based on their immune status would be a cost effective approach.

Evaluation of the time resolved fluorescence immunoassay (TRFIA) for the detection of varicella zoster virus (VZV) antibodies following vaccination of healthcare workers

Determination of varicella zoster virus (VZV) immunity in healthcare workers without a history of chickenpox is important for identifying those in need of vOka vaccination. Post immunisation, healthcare workers in the UK who work with high risk patients are tested for seroconversion. To assess the performance of the time-resolved fluorescence immunoassay (TRFIA) for the detection of antibody in vaccinated as well as unvaccinated individuals, a cut-off was first calculated. VZV-IgG specific avidity and titres six weeks after the first dose of vaccine were used to identify subjects with pre-existing immunity among a cohort of 110 healthcare workers. Those with high avidity (≥ 60%) were considered to have previous immunity to VZV and those with low or equivocal avidity (<60%) were considered naive. The former had antibody levels ≥ 400 mIU/mL and latter had levels < 400 mIU/mL. Comparison of the baseline values of the naive and immune groups allowed the estimation of a TRFIA cut-off value of > 130 mIU/mL which best discriminated between the two groups and this was confirmed by ROC analysis. Using this value, the sensitivity and specificity of TRFIA cut-off were 90% (95% CI 79-96), and 78% (95% CI 61-90) respectively in this population. A subset of samples tested by the gold standard Fluorescence Antibody to Membrane Antigen (FAMA) test showed 84% (54/64) agreement with TRFIA.

How reliable is the history of chickenpox? Varicella serology among children up to 14 years of age

OBJECTIVES

The aim of this study was to assess the seroprevalence of antibodies to varicella-zoster virus (VZV) in children of northern Greece and to estimate the reliability of varicella history.

METHODS

A serosurvey of 632 children, aged 13 months to 14 years (median 5.2 years), was conducted between April 1999 and July 2001. Serum samples were tested by enzyme-linked immunosorbent assay (ELISA) for IgG antibodies to VZV (IgG Genzyme Virotech GmbH). A history of varicella in these children was obtained from the parents of all these patients. Also, a check of state health cards of the patients was done.

RESULTS

Two hundred and forty-eight (39%) of the children were seropositive for VZV. Two hundred and thirty (36%) of the 632 children claimed to have had previous varicella infection; 87.8% were seropositive, and 12.2% lacked antibodies to VZV. One hundred and seven of the 230 children with a history of varicella had the information about the disease confirmed, as it was reported on their state health card by a pediatrician; 10.2% were seronegative for VZV. Absence of history of varicella was reported in 402 (63.6%) of the 632 children; 88.6% of those were seronegative, and 11.4% were seropositive. The percentage of incorrect negative history ranged from 6% (13-60 months of age) to 48% (120-168 months of age).

CONCLUSIONS

A large proportion of the study group (61%), mainly below 7 years of age, is susceptible to varicella. The positive predictive value of a history of varicella is 87.8%, whereas the negative predictive value of a negative history is 11.4%, which means that there is an 88.6% probability of a negative history being correct. Varicella serology may be reasonable prior to vaccination in children >10 years old with a negative chickenpox history. However, if one excludes cost considerations, it is also reasonable to vaccinate all children, irrespective of serostatus.

Comparison of fluorescent-antibody-to-membrane-antigen test, indirect immunofluorescence assay, and a commercial enzyme-linked immunosorbent assay for determination of antibody to varicella-zoster virus

The demand for sensitive and specific assays to determine immune status to varicella can be expected to increase with the anticipated availability of a varicella-zoster virus vaccine for use in nonimmune adults, especially health care personnel, and in immunosuppressed children. Although the fluorescent-antibody-to-membrane-antigen (FAMA) test remains the reference standard to which other tests are compared, simpler alternative assays are needed. In this study, the FAMA was compared with a simple indirect immunofluorescence assay (IFA) and a commercially available enzyme-linked immunosorbent assay (ELISA) for the detection of antibody to varicella-zoster virus. One hundred and twelve serum samples were screened by the FAMA test and IFA at a 1:5 dilution, and 100% agreement was found. Of these samples, 101 were available for testing by ELISA, and identical results were obtained with 97 samples (96% agreement). When the samples were screened at a 1:2 dilution, 99 of 101 results agreed. In addition, 31 spinal fluid samples were tested by all three methods. When screening was at a 1:2 dilution, there was 96.8% agreement between the FAMA test and IFA. When the cutoff value established for sera was used for the spinal fluid samples, there was 90.3% agreement between the ELISA and the FAMA test. Thus, both IFA and ELISA can be considered sensitive and specific alternatives to the FAMA test, and in addition, both use commercially available reagents.

The potency determination of human varicella-zoster immunoglobulin by enzyme-linked immunosorbent assay, complement-fixation test and indirect fluorescent antibody tests

Traditionally, plasma for the production of the human varicella-zoster immunoglobulin (VZIG) has been selected on the basis of the complement-fixing antibody (CFA) titre. Since immune individuals may lack CFA to varicella-zoster virus (VZV), non-CFA may be of importance in protection. In a search for a simple and reliable method for potency determination, 24 VZIG preparations were quantified by enzyme-linked immunosorbent assay (ELISA), the complement-fixation test (CFT), the indirect fluorescent antibody test to acetone-fixed (IF) and viable (FAMA) VZV-infected cells, respectively. The antibody titres obtained by the various methods were compared. Arranged in order of decreasing agreement, the correlation coefficients (r) of the regression equations between the variables were 0.62 for CFT and FAMA, 0.50 for CFT and ELISA and 0.26 for CFT and IF in a log2 plot. There was complete agreement between the titres obtained by the commercially available Enzygnost Varicella/Zoster kits (Behring Institute, Marburg, F.R. Germany) and the ELISA microtitre plates produced at our institute (r = 1). The regression equation lines for ELISA/CFT and FAMA/CFT titres tended to be parallel to each other, while the line for IF/CFT titres had a less steep slope. Similar titration curves were obtained for VZIGs fractionated by two different methods. Furthermore, the titration curves of serum pools from varicella and zoster convalescents, respectively, had a similar shape below delta OD = 0.4. Generally, a steeper slope was observed above delta OD = 0.4. As antibody detectable by ELISA seems to correlate with protection and the method is sensitive, specific, reproduceable, simple to carry out and easily automated, it may be suitable for the potency determination of VZIGs.