AUTHOR=Mo Zequan , Wu Huicheng , Hu Yingtong , Lai Xueli , Guo Wenjie , Duan Yafei , Dan Xueming , Li Yanwei 

TITLE=Protection of Grouper Against Cryptocaryon irritans by Immunization With Tetrahymena thermophila and Protective Cross-Reactive Antigen Identification

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.891643

DOI=10.3389/fimmu.2022.891643

ISSN=1664-3224

ABSTRACT=<p>Vaccination is an effective method to prevent <italic>Cryptocaryon irritans</italic> infection. Although some vaccines have been developed, large-scale production of these vaccines is costly. Development of a heterogenous vaccine generated by low-cost antigens is an alternative method. In the present study, grouper immunized with <italic>Tetrahymena thermophila</italic>, a free-living ciliate that easily grows in inexpensive culture media at high density, showed protective immunity against <italic>C. irritans</italic> infection. Higher immobilization against <italic>C. irritans</italic> theronts was detected in <italic>T. thermophila</italic>–immunized grouper serum, which suggested the existence of a cross-reactive antibody in the serum. By immunoprecipitation and mass spectrometry analyses, tubulin was identified as a potential cross-reactive antigen between <italic>C. irritans</italic> and <italic>T. thermophila</italic>. Recombinant <italic>T. thermophila</italic> tubulin protein (rTt-tubulin) and its antibody were prepared, and immunofluorescence showed that both <italic>C. irritans</italic> and <italic>T. thermophila</italic> cilia were stained by the anti–rTt-tubulin antibody. Grouper immunized with rTt-tubulin showed a reduced infective rate after the <italic>C. irritans</italic> challenge. An enhanced level of <italic>C. irritans</italic>–binding immunoglobulin M (IgM) antibody was detected in serum from rTt-tubulin–immunized grouper. Moreover, specific antibodies were also found in the mucus and tissue culture medium from rTt-tubulin–immunized grouper. Overall, these findings suggested that vaccination with <italic>T. thermophila</italic> elicits cross-reactive protective immunity in grouper against <italic>C. irritans</italic>, and <italic>T. thermophila</italic> may be a potential heterologous antigen for vaccine development.</p>