|Van Santen, Vicky|
Submitted to: Aquaculture Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/24/2009
Publication Date: 7/13/2009
Citation: Xu, D., Panangala, V.S., Van Santen, V.L., Dybvig, K., Abernathy, J.W., Klesius, P.H., Liu, Z., Russo, R. 2009. Molecular characteristics of an immobilization antigen gene of the fish-parasitic protozoan Ichthyophthirius multifiliis strain ARS-6. Aquaculture Research. 40(16): 1884-1892.
Interpretive Summary: The fish parasite, Ichthyophthirius multifiliis (Ich), infests many freshwater fish and lead to heavy loss in aquaculture. Fish surviving from I. multifiliis infestation are known to possess antibodies against Ich and antibodies from the immune fish are capable of immobilizing the parasite. In order to develop effective vaccine to prevent the parasite infestation, it is necessary to understand antigens on the parasite surface that are involved in the antibody-mediated immobilization (immobilization antigens or i-antigens) and genes encoded i-antigens. In this study, nucleotide sequence of an i-antigen gene of Ich strain ARS-6 was describe and the deduced amino acid sequence was compared with those of presently known amino acid sequences of Ich collected from other locations. The degree of deduced i-antigen amino acid sequence identity of strain ARS-6 with other Ich i-antigen sequences present in GenBank ranges from 99% to 36%. Immunoblot analysis of i-antigens following exposure of ARS-6 theronts to catfish anti-Ich immune serum did not show any appreciable alteration in i-antigen expression. The result is important in understanding the difference on Ich i-antigen sequences among different Ich strains. This information is essential to university, academic, and researchers for development of anti-parasitic vaccine, which would have worldwide impact in preventing the disease and minimizing fish losses due to Ich infestation.
Technical Abstract: Ichthyophthirius multifiliis, a ciliated protozoan parasite of fish, expresses surface antigens (i-antigens), which react with host antibodies that render them immobile. The nucleotide sequence of an i-antigen gene of Ichthyophthirius multifiliis strain ARS-6 was deduced. The predicted protein of 47,493 Da is comprised of 460 amino acids (aa’s) arranged into five imperfect repeats with periodic cysteine residues with the structure: CX(19)20CX2CX16-27CX2CX20(21)CX3 . The N-terminal aa’s typify a signal peptide motif while a stretch of C-terminal aa’s resemble a glycosyl-phosphatidyl-inositol (GPI)-anchor addition site. The degree of deduced i-antigen aa sequence identity of strain ARS-6 (GenBank accession # ACH87654) with other I. multifiliis i-antigen sequences present in GenBank ranges from 99% identity to 36% identity with 52 kDa i-antigens of I. multifiliis strain G5 (accession #s AAK94941 and AAK01661 respectively). Immunoblot analysis of i-antigens following exposure of I. multifiliis theronts to catfish anti-I. multifiliis immune serum did not show any appreciable alteration in i-antigen expression. The mechanism that regulates i-antigen expression in I. multifiliis remains a puzzling question.