AUTHOR=Yao Jia-Yun , Zhang Cheng-Sai , Yuan Xue-Mei , Huang Lei , Hu Da-Yan , Yu Zhe , Yin Wen-Lin , Lin Ling-Yun , Pan Xiao-Yi , Yang Gui-lian , Wang Chun-Feng , Shen Jin-Yu , Zhang Hai-Qi 

TITLE=Oral Vaccination With Recombinant Pichia pastoris Expressing Iridovirus Major Capsid Protein Elicits Protective Immunity in Largemouth Bass (Micropterus salmoides)

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.852300

DOI=10.3389/fimmu.2022.852300

ISSN=1664-3224

ABSTRACT=<p>Largemouth bass iridovirus (LMBV) can cause high mortality and lead to heavy economic loss in the cultivation of largemouth bass, but there was no effective treatment. Here, the present study constructed a recombinant <italic>Pichia pastoris</italic> expressing LMBV major capsid protein (<italic>MCPD</italic>). The recombinant GS115-pW317-<italic>MCPD</italic> was then used to immunize largemouth bass <italic>via</italic> oral administration, and mucosal immune response mediated by immunoglobulins (Igs) was measured after oral immunization. Serum antibody levels were measured by ELISA, neutralizing antibody titers were determined by serum neutralization test (SNT), antigen presentation-related gene expressions were detected by RT-PCR, and the histopathological characteristics of immunized fish were assessed after challenging with 0.1 ml 10<sup>7.19</sup> TCID<sub>50</sub>/ml LMBV. The relative percentage survival (RPS) was also determined. Our results showed that the serum antibody titers of immunized fish were significantly higher than that of control groups (P &lt; 0.05). IgT and IgM expressions in gut were increased significantly after vaccination with GS115-pW317-<italic>MCPD</italic>; however, much stronger response in gut was observed as compared with gill. The expression levels of major histocompatibility complex (<italic>MHC</italic>) II, <italic>CD</italic>8, and T-cell receptor (<italic>TCR</italic>) were significantly elevated in GS115-pW317-<italic>MCPD</italic> group (P &lt; 0.05), while <italic>CD</italic>4 and <italic>MHC</italic> I transcription levels remained unchanged after oral immunization (<italic>P</italic> &gt; 0.05). The RPS of fish orally immunized with 1.0 × 10<sup>8</sup> CFU/g GS115-pW317-<italic>MCPD</italic> was reached up to 41.6% after challenge with 0.1 ml 10<sup>9.46</sup> TCID<sub>50</sub>/ml LMBV. Moreover, orally immunizing with GS115-pW317-<italic>MCPD</italic> can relieve the pathological damage caused by LMBV. Therefore, GS115-pW317-<italic>MCPD</italic> showed a promising potential against LMBV.</p>