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

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

PLOS NEGLECTED TROPICAL DISEASES

PUBLIC LIBRARY SCIENCE

Lugar: San Francisco; Año: 2016

1935-2735

AbstractThe larva of cestodes belonging to the Echinococcus granulosus sensu lato (s.l.)complex causes cystic echinococcosis (CE). It is a globally distributed zoonosis withsignificant economic and public health impact. The most immunogenic and specificEchinococcus-genus antigen for human CE diagnosis is antigen B (AgB), an abundantlipoprotein of the hydatid cyst fluid (HF). The AgB protein moiety (apolipoprotein) isencoded by five genes (AgB1-AgB5), which generate mature 8 kDa proteins (AgB8/1-AgB8/5). These genes seem to be differentially expressed among Echinococcusspecies. Since AgB immunogenicity lies on its protein moiety, differences in AgBexpression within E. granulosus s.l. complex might have diagnostic andepidemiological relevance for discriminating the contribution of distinct species tohuman CE. Interestingly, AgB2 was proposed as a pseudogene in E. canadensis,which is the second most common cause of human CE, but proteomic studies forverifying it have not been performed yet. Herein, we analysed the protein and lipidcomposition of AgB obtained from fertile HF of swine origin (E. canadensis G7genotype). AgB apolipoproteins were identified and quantified using massspectrometry tools. Results showed that AgB8/1 was the major protein component, representing 71% 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, aparallel analysis detected all AgB apolipoproteins in bovine fertile HF (G1/3/5genotypes). Overall, E. canadensis AgB comprised mostly AgB8/1 together with aheterogeneous mixture of lipids, and AgB8/2 was not detected despite using highsensitivity proteomic techniques. This endorses genomic data supporting that AgB2behaves as a pseudogene in G7 genotype. Since recombinant AgB8/2 has been foundto be diagnostically valuable for human CE, our findings indicate that its use as antigenin immunoassays could contribute to false negative results in areas where E.canadensis circulates. Furthermore, the presence of anti-AgB8/2 antibodies in serummay represent a useful parameter to rule out E. canadensis infection when human CEis diagnosed.