Identification of the immunodominant regions of the Em18 antigen and improved serodiagnostic specificity for alveolar echinococcosis.
The aim of this work was to identify the immunodominant regions of the Em18 antigen to improve the specificity in diagnosis of alveolar echinococcosis (AE). Two recombinant antigens ReEm18-1 and ReEm18-2, which have the same sequence except that nine amino acid residues are absent in ReEm18-2, were tested by ELISA and Western Blot (WB) for their diagnostic efficiency. Serological evaluation of the two antigens demonstrated that the sensitivity of both antigens was 95.5% in ELISA and WB, and the specificity was 93.6% and 95.7% in ELISA, and 81.4% and 82.9% in WB, respectively. Five more expression clones (EmS1-EmS5), which contain different regions of the Em18 sequence, were constructed for defining the immunodominant regions of the antigen. Fourteen monoclonal antibodies (mAbs) against ReEm18-2 antigen and the sera from different groups of patients were used to identify the epitope regions of the five antigen fragments. Results showed that the epitopes recognized by the mAbs are located in the N-terminal third of the sequence, but the immunodominant area recognized by native serum antibodies may be located further downstream (C-terminal) in the sequence. The nonspecific cross-reactivity is due to epitopes present in the C-terminal third of the sequence. The antigen fragments that contain the first two-thirds of the sequence have the same sensitivity to AE sera as those of the ReEm18-1 and ReEm18-2 antigens, but removal of the C-terminal third of the sequence improved the specificity of the assay from 93.6% to 99.3% (ELISA) and 81.4% to 90.7% (WB). We conclude that the necessary part of the ReEm18 antigen sequence for AE diagnosis is the N-terminal half to two-thirds of the entire sequence.
Jiang
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National Institute of Parasitic Diseases, Chinese Centre for Disease Control and Prevention, Shanghai 200025, China.
Xu
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XN
Li
X
X
Xue
H-C
HC
Feng
Z
Z
D000818:Animals; D000909:Antibodies, Helminth / Q000097:blood* / Q000235:genetics / Q000276:immunology; D000911:Antibodies, Monoclonal / Q000276:immunology; D000947:Antigens, Helminth / Q000235:genetics / Q000276:immunology*; D015153:Blotting, Western; D002681:China; D003001:Cloning, Molecular; D003429:Cross Reactions; D004445:Echinococcosis, Pulmonary / Q000175:diagnosis* / Q000276:immunology / Q000469:parasitology; D048210:Echinococcus multilocularis / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D018604:Epitope Mapping; D006801:Humans; D016056:Immunodominant Epitopes / Q000235:genetics / Q000276:immunology*; D011994:Recombinant Proteins / Q000235:genetics / Q000276:immunology; D012680:Sensitivity and Specificity; D017384:Sequence Deletion; D012698:Serologic Tests
D000909:Antibodies, Helminth; D000911:Antibodies, Monoclonal; D000947:Antigens, Helminth; C117889:Em18 antigen; D016056:Immunodominant Epitopes; D011994:Recombinant Proteins