Comparative immunodiagnostic performance of AgB1-derived synthetic peptides in human cystic echinococcosis

Immunoassays are complementary diagnostic tools in human cystic echinococcosis (CE) despite sensitivity/specificity limitations, and synthetic peptides have been suggested to potentially overcome disadvantages reported for traditional antigens. Herein, a systematic study comparing the immunodiagnostic performance of AgB1 versus synthetic peptides derived from its sequence was carried out. Thus, a eukaryotic-expressed recombinant AgB1 was assessed, together with a reported synthetic peptide (p176, N-terminal portion of AgB1) and two new peptides within p176 (namely pB1a and pB1b) corresponding to predicted linear B-cell epitopes. Immunodiagnostic performances were evaluated by ELISA using a large collection of human sera from CE patients, healthy donors, and individuals with other parasitoses; assessing the sensitivity, specificity, indeterminacy, cross-reactivity, and diagnostic efficiency of the assay according to each antigen. Results suggest that peptides retaining most of the original protein sequence and 3D-structure display better overall diagnostic efficiencies (IgG_t values for rAgB1, p176, pB1a, and pB1b were 66.1%, 60.4%, 54.7%, and 49.0%, respectively), with a small N-terminal portion of AgB1 being immunodominant. Additionally, detection of specific IgG₄ antibodies significantly reduced cross-reactivity, while improving sensitivity (IgG_t-IgG₄ values for rAgB1, p176, and pB1a were
37.5%–42.7%, 24.0%–29.2%, and 11.5%–24.0%, respectively). Valuable information was obtained for rationally design novel peptide-based assays for CE immunodiagnosis.