Characterisation of Antigen B protein species present in the hydatid cyst fluid of Echinococcus canadensis G7 genotype

LIMA A; MOURGLIA-ETTLIN G; BATTHYÁNY C; KITANO ES; CUCHER M; ROSENZVIT M C; FOLLE AM; GIL M; IWAI LK; FERREIRA AM

PLoS Neglected Tropical Diseases

Public Library of Science

Lugar: San Francisco; Año: 2017 vol. 11

1935-2727

AbstractThe larva of cestodes belonging to the Echinococcus granulosus sensu lato (s.l.) complexcauses cystic echinococcosis (CE). It is a globally distributed zoonosis with significanteconomic and public health impact. The most immunogenic and specific Echinococcusgenusantigen for human CE diagnosis is antigen B (AgB), an abundant lipoprotein of thehydatid cyst fluid (HF). The AgB protein moiety (apolipoprotein) is encoded by five genes(AgB1-AgB5), which generate mature 8 kDa proteins (AgB8/1-AgB8/5). These genesseem to be differentially expressed among Echinococcus species. Since AgB immunogenicitylies on its protein moiety, differences in AgB expression within E. granulosus s.l.complex might have diagnostic and epidemiological relevance for discriminating the contributionof distinct species to human CE. Interestingly, AgB2 was proposed as a pseudogenein E. canadensis, which is the second most common cause of human CE, butproteomic studies for verifying it have not been performed yet. Herein, we analysed theprotein and lipid composition of AgB obtained from fertile HF of swine origin (E. canadensisG7 genotype). AgB apolipoproteins were identified and quantified using massspectrometry tools. Results showed that AgB8/1 was the major protein component, representing71% of total AgB apolipoproteins, followed by AgB8/4 (15.5%), AgB8/3 (13.2%)and AgB8/5 (0.3%). AgB8/2 was not detected. As a methodological control, a parallelanalysis detected all AgB apolipoproteins in bovine fertile HF (G1/3/5 genotypes). Overall,E. canadensis AgB comprised mostly AgB8/1 together with a heterogeneous mixtureof lipids, and AgB8/2 was not detected despite using high sensitivity proteomic techniques.This endorses genomic data supporting that AgB2 behaves as a pseudogene inG7 genotype. Since recombinant AgB8/2 has been found to be diagnostically valuable forhuman CE, our findings indicate that its use as antigen in immunoassays could contributeto false negative results in areas where E. canadensis circulates. Furthermore, the presence of anti-AgB8/2 antibodies in serum may represent a useful parameter to rule outE. canadensis infection when human CE is diagnosed.