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The time resolved
fluorescence antibody assay may be useful as a screening assay for
the diagnosis of chlamydial infection.
Measurement of IgG
antibodies to Chlamydia trachomatis by commercial enzyme
immunoassays and immunofluorescense in sera from pregnant women and
patients with infertility, pelvic inflammatory disease, ectopic
pregnancy, and laboratory diagnosed Chlamydia psittaci/Chlamydia
pneumoniae infection.
Jones CS, Maple PAC, Andrews NJ, Paul
ID, Caul EO.
J Clin Pathol. 2003;56:225-230.
Summary:
Question
How well do the performances of commercial enzyme immunoassays compare to
that of the whole cell inclusion immunofluorescence test for the detection
of antibodies to C. trachomatis, and can one be adapted as a
screening assay for predicting upper genital tract infection using time
resolved fluorescence technology?
Design
The performance of seven commercial enzyme immunoassays (EIAs), utilizing
different C. trachomatis antigens, was compared to a whole cell
inclusion immunofluorescence assay (WIF) for the detection of C.
trachomatis IgG antibodies in a selected panel of serum samples. One
EIA was modified, using a time resolved fluorescence immunoassay (TRFI),
for use as a screening test to detect women with upper genital tract
disease.
Participants
A set of 436 sera was assembled for comparison testing including 90 from
women with ectopic pregnancies, 187 from patients with infertility, 33
from cases of PID shown by at least a fourfold increase in titer, 36 from
cases of C. psittaci or C. pneumoniae (diagnosed by WIF),
and 90 from antenatal women.
Description of Tests and Diagnostic
Standard
Seven EIA tests, performed according to the manufacturers' instructions,
were used to detect C. trachomatis IgG in the serum panel. Platelia
Chlamydia IgG (Sanofi Diagnostics Pasteur Ltd., Guilford, UK) is a genus
specific EIA; the other six assays are species specific. Chlamydia
trachomatis EIA (Genzyme Virotech, Russelsheim, Germany) uses a C.
trachomatis LGV type II strain, cultured in mouse L cells, and
inactivated using gamma irradiation, as the antigen. Chlamydia
trachomatis IgG/IgM EIA (Vircell SL, Microgen Bioproducts Ltd.,
Camberley, UK) uses extracted and purified native MOMP as the antigen,
while SeroCT-IgG (Savyon Diagnostics Ltd.), C. tracho EIA-IgG (PBS
Orgenics), Chlamydia trachomatis-IgG-pEIA (Medac Diagnostics, Wedel,
Germany), and Chlamydia trachomatis IgG EIA (Labsystems, Quest
Biomedical, Knowle, UK) use peptides from regions of the MOMP protein.
The reference assay for measuring C.
trachomatis specific antibodies was the WIF, a single antigen
immunofluorescence test in which cytochalasin B-treated McCoy cells
infected with an LGV type 2 strain of C. trachomatis are placed in
the test wells so that the whole chlamydial inclusion acts as the antigen.
The WIF test detects both genus-specific LPS and species-specific MOMP
antibodies. Enzootic abortion ewes C. psittaci and C. pneumoniae
TW 183 were used for C. psittaci and C. pneumoniae specific
antibody detection, respectively.
For the TFRI assay, sera were diluted
1:64 and added to wells of the Genzyme Virotech EIA plates. The plates
were incubated for 2 h at 37oC and washed. Europium-labeled
antihuman IgG conjugate (Wallac Oy), diluted 1:500, was added. The plates
were incubated, washed, and the fluorescence read. Forty-five sera with
WIF titers >512 (the cut-off used for predicting genital tract
infection) and 22 with titers <512 were tested.
Main Outcome Measures
The results of the EIA assays were compared to those of the WIF using
Spearman's coefficient of rank correlation (r) with 95% confidence
intervals (CI). The number of negative results for each EIA was determined
for the 36 sera diagnosed by WIF as C. pneumoniae or C. psittaci.
Main Results
The correlation between the commercial EIA and the WIF results for the 400
test sera, and the number of negative results by EIA for the 36 C.
psittaci/C pneumoniae positive sera are shown in the table. When the
Genzyme Virotech EIA, which correlated most closely with the WIF, was used
in the TRFI assay, all 45 samples positive by WIF had fluorescent signals
above 100,000 counts.
Authors' Conclusions
The Genzyme Virotech EIA modified using TRFI
appeared to be highly successful in differentiating between WIF positive
and negative sera. This assay can be used as a screening tool to detect
sera with high chlamydial antibody titers, which can be further tested for
C. trachomatis-specific MOMP antibody by a more specific assay such as the
Medac p-EIA.
Source of funding:
None given
For correspondence: P. A. C. Maple,
Public Health Laboratory, Myrtle Road, Bristol BS2 8EL, UK. E-mail
address: cmaple@phls.org.uk.
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