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Clinical and Diagnostic Laboratory Immunology, January 1999, p. 24-29, Vol. 6, No. 1
Innogenetics NV,
Received 10 July 1998/Accepted 7 October 1998
Dense granule protein 7 (GRA7) of Toxoplasma gondii was
expressed in Escherichia coli as a fusion protein. The
leader peptide contained a 25-amino-acid mouse tumor necrosis factor
fragment and six histidyl residues. After purification by metal chelate affinity chromatography, the antigen was evaluated in an enzyme-linked immunosorbent assay for detection of immunoglobulin G (IgG). For two
sets of IgG-positive human serum samples, obtained from routine screening, an overall sensitivity of 81% was obtained. For
chronic-phase sera, the sensitivity of detection was 79%, but
chronic-phase sera with low titers were more difficult to detect (65%
sensitivity for sera with immunofluorescence titer of 1/64). When GRA7
was combined with Tg34AR (rhoptry protein 2 C-terminal fragment), the
sensitivity rose to 96%. For a set of acute-phase serum samples tested
on GRA7, the sensitivity of detection was 94%, and high-titer IgM-positive sera were detected at an especially high rate. In contrast, when Tg34AR was used, the sensitivity was only 85% for this
latter set of serum samples. Three truncated GRA7 fragments containing
the same leader peptide as that of recombinant GRA7 were produced. The
shortest fragment (97 N-terminal amino acids) was not reactive with
human sera or with a specific anti-GRA7 monoclonal antibody, while the
two larger fragments were reactive. The most important antigenic domain
of GRA7 for human sera was localized between residues 97 and 146. The
epitope for the specific monoclonal antibody could be further
narrowed down by the use of synthetic peptides, but this epitope is
not recognized by sera from T. gondii-infected humans.
These results indicate that GRA7 may be considered as an additional
tool for studying the immune response to T. gondii.
1071-412X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Evaluation of Recombinant Dense Granule Antigen 7 (GRA7) of Toxoplasma gondii for Detection of Immunoglobulin
G Antibodies and Analysis of a Major Antigenic Domain
*
Corresponding author. Mailing address: Innogenetics
N.V., Industriepark Zwijnaarde 7, B-9052 Gent, Belgium. Phone:
32-9-2410803. Fax: 32-9-2410907. E-mail:
dirkjac{at}innogenetics.be.
Clinical and Diagnostic Laboratory Immunology, January 1999, p. 24-29, Vol. 6, No. 1
1071-412X/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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