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Clinical and Diagnostic Laboratory Immunology, February 2005, p. 359-360, Vol. 12, No. 2
1071-412X/05/$08.00+0 doi:10.1128/CDLI.12.2.359-360.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.
Performance of Two Commercial Enzyme-Linked Immunosorbent Assay Kits Using Recombinant Glycoprotein G2 Antigen for Detection of Herpes Simplex Virus Type 2 Specific Antibodies
Sharmila M. Reddy,1
P. Balakrishnan,1*
S. Uma,1
S. P. Thyagarajan,2 and
Suniti Solomon1
YRG CARE, Centre for AIDS Research and Education,1
University of Madras, Chennai, India2
Received 22 July 2004/
Returned for modification 15 September 2004/
Accepted 17 November 2004

ABSTRACT
For 93 stored serum samples tested by HerpeSelect2 and the Euroimmun
enzyme-linked immunosorbent assay for detection of herpes simplex
virus type 2-specific immunoglobulin G antibodies, the concordance
of positive and negative results was 100%. Moreover, all the
results that were equivocal by HerpeSelect2 (negative by Euroimmun)
were confirmed as being negative by a Western blot assay.

TEXT
Genital herpes, which is predominantly caused by infection with
herpes simplex virus type 2 (HSV-2), is one of the most common
sexually transmitted diseases. Studies suggest that HSV-2 plays
an important role in the transmission of human immunodeficiency
virus infection in persons with high-risk behavior (
1,
3-
5,
9,
14). In clinically recognized disease, virus isolation or
antigen detection from vesicular or ulcerative lesions is the
preferred diagnostic method, but isolation may be difficult
if lesions are crusted, healed, or absent (
9,
13). Moreover,
for community-based cross-sectional studies with asymptomatic
populations, serological diagnosis is most commonly preferred
(
2,
3,
7,
8,
10). In recent years, HSV glycoprotein G (gG) has
been identified as a viral protein that is type specific for
HSV-2. Detection of antibodies produced against this gG has
been proven useful for the diagnosis of primary genital herpes
and as a screening test for asymptomatic pregnant women (
8,
10,
13). Glycoprotein G-based enzyme-linked immunosorbent assays
(ELISAs) for HSV-1 and HSV-2 are highly divergent and typically
elicit very limited humoral cross-reactivity (
11,
12). Therefore,
the detection of gG2 antibodies is a reliable indicator of past
or present HSV-2 infection. The aim of the present study was
to investigate the performance of the Euroimmun kit in comparison
with that of the U.S. Food and Drug Administration-approved
HerpeSelect 2 kit.
A total of 93 serum samples stored at 70°C were randomly selected and tested by the HerpeSelect and Euroimmun (Lübeck, Germany) ELISA kits for HSV-2 immunoglobulin G (IgG) according to the manufacturer's instructions. The principles of HerpeSelect and Euroimmun are as follows: HerpeSelect provides a qualitative assay, and Euroimmun provides a semiquantitative or quantitative assay, for IgG class antibodies to HSV-2 in human serum. Both ELISA kits require that diluted serum samples and controls be incubated in the gG2 antigen-coated wells to allow the specific antibody present in the samples to react with the antigen. Peroxidase-conjugated anti-human IgG is added and reacts with specific IgG. An enzyme substrate and chromogen are added, and the color is allowed to develop. Color change is quantified by a spectrophotometric reading of optical density. HerpeSelect requires a 1:101 dilution of serum; high-positive, low-positive, and negative controls; and a calibrator. Euroimmun has ready-to-use (prediluted for 1:101) positive and negative controls, and calibrator 2. HerpeSelect requires a 1-h serum incubation and a 10-min substrate incubation, whereas Euroimmun requires a 30-min serum incubation and a 15-min substrate incubation. In HerpeSelect, an index value is obtained for each sample run, based on the absorbance of the patient sample divided by the mean absorbance of the cutoff calibrator; an index value of <0.9 is considered negative, a value of
0.9 but
1.1 is considered equivocal, and a value of >1.1 is considered positive. In the Euroimmun ELISA, an index value is obtained for each sample based on the absorbance of the patient sample divided by the absorbance of cutoff calibrator 2. A ratio of <1.0 is considered negative, and a ratio of
1.0 is considered positive. All the positive and negative results by the HerpeSelect ELISA were 100% in concordance with those of the Euroimmun ELISA. Of 93 randomly selected samples, 35 were positive and 35 were negative by both the kits. However, 23 samples that were equivocal by HerpeSelect were negative by the Euroimmun kit.
To confirm the results obtained by the two ELISA kits and the status of the equivocal samples, a Euroline Western blot (WB) assay was performed. The Euroline HSV-1/HSV-2 gG2 (IgG) WB kit (Euroimmun) is a commercially available kit that can differentiate between specific antibodies against HSV-1 and HSV-2. Sixteen samples positive by both ELISAs and 16 samples negative by both ELISAs were randomly chosen, as well as all 23 equivocal (by HerpeSelect) samples, and Western blotting was carried out according to the manufacturer's instructions. All 16 samples positive for HSV-2 and all 16 samples negative for HSV-2 were confirmed by the WB assay (Table 1). All 23 samples that were equivocal by HerpeSelect turned out to be negative for HSV-2 by the WB assay (Table 1), confirming the result obtained with the Euroimmun ELISA kit. Of these 23 equivocal samples, 20 were positive and 3 were negative for the presence of HSV-1 antibodies by the WB assay. Of 16 HSV-2-negative samples, 13 were positive for HSV-1 antibodies by the WB assay. Hence, the HerpeSelect ELISA has considerable cross-reactivity with the antigen of HSV-1.
Our study has shown that the Euroimmun ELISA for HSV-2 IgG is
100% sensitive and specific. A similar performance has been
observed in a recent study (
6). However, these two assays with
gG2 protein disagreed for 23 (25%) of the 93 serum samples analyzed.
This demonstrates the problem related to the use of a gG2 assay
as the sole criterion for HSV-2 diagnosis. Therefore, an assay
that measures immune responses to a single viral protein or
to an individual epitope may be problematic, and an assay based
on a viral antigen other than gG2, such as that described in
a recent study (
15), is needed. The present study was limited
by the use of the WB assay kit from Euroimmun. Also, further
studies with the Euroimmun ELISA are required to show the robustness
and reproducibility of the results before this kit is considered
for use in research and diagnosis of patients in developing
countries.

ACKNOWLEDGMENTS
We acknowledge CPC Pharmaceuticals Pvt. Ltd., Chennai, India,
for funding this study.

FOOTNOTES
* Corresponding author. Mailing address: YRG CARE, Centre for AIDS Research and Education, VHS, Taramani, Chennai 600 113, India. Phone: 91-44-22542929. Fax: 91-44-22542939. E-mail:
bala{at}yrgcare.org.


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Clinical and Diagnostic Laboratory Immunology, February 2005, p. 359-360, Vol. 12, No. 2
1071-412X/05/$08.00+0 doi:10.1128/CDLI.12.2.359-360.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.