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Infect Immun, February 1998, p. 717-723, Vol. 66, No. 2
Institute of Immunology and Rheumatology,
University of Oslo, N-0172 Oslo, Norway1;
Department of Clinical Sciences, London School of Hygiene
and Tropical Medicine, London, United
Kingdom2; and
Chemical Institute,
Received 15 May 1997/Returned for modification 26 June
1997/Accepted 10 July 1997
ESAT-6 is an important T-cell antigen recognized by protective T
cells in animal models of infection with Mycobacterium
tuberculosis. In an enzyme-linked immunosorbent assay (ELISA)
with overlapping peptides spanning the sequence of ESAT-6, monoclonal
antibody HYB76-8 reacted with two peptides in the N-terminal region of the molecule. Assays with synthetic truncated peptides allowed a
precise mapping of the epitope to the residues EQQWNFAGIEAAA at
positions 3 to 15. Hydrophilicity plots revealed one hydrophilic area
at the N terminus and two additional areas further along the
polypeptide chain. Antipeptide antibodies were generated by immunization with synthetic 8-mer peptides corresponding to these two
regions coupled to keyhole limpet hemocyanin. Prolonged immunization with a 23-mer peptide (positions 40 to 62) resulted in the formation of
antibodies reacting with the peptide as well as native ESAT-6. A
double-antibody ELISA was then developed with monoclonal antibody HYB76-8 as a capture antibody, antigen for testing in the second layer,
and antipeptide antibody in the third layer. The assay was suitable for
quantification of ESAT-6 in M. tuberculosis antigen preparations, showing no reactivity with M. bovis BCG Tokyo
culture fluid, used as a negative control, or with MPT64 or antigen
85B, previously shown to cross-react with HYB76-8. This capture ELISA permitted the identification of ESAT-6 expression from vaccinia virus
constructs containing the esat-6 gene; this expression
could not be identified by standard immunoblotting.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
B-Cell Epitopes and Quantification of the ESAT-6
Protein of Mycobacterium tuberculosis
*
Corresponding author. Mailing address: Institute of
Immunology and Rheumatology, University of Oslo, Fr. Qvams gate 1, N-0172 Oslo, Norway. Phone: 47 22 03 31 70. Fax: 47 22 20 72 87. E-mail: morten.harboe{at}labmed.uio.no.
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