Deleting ORF71L of infectious spleen and kidney necrosis virus (ISKNV) resulted in virulence attenuation in Mandarin fish. Issue 123 (April 2022)

• Record Type: Journal Article
• Authors: Zhang, Hetong; Qi, Hemei; Weng, Shaoping; He, Jianguo; Dong, Chuanfu
• Is Part Of: Fish & shellfish immunology. Issue 123(2022)
• Page Start: 335
• Page End: 347
• Publication Date: 2022-04
• Subjects: ISKNV -- Megalocytivirus -- Virulence -- Recombination -- Mandarin fish; Fishes -- Immunology -- Periodicals; Shellfish -- Immunology -- Periodicals; Poissons -- Immunologie -- Périodiques; Crustacés -- Immunologie -- Périodiques; 571.9617
• DOI: 10.1016/j.fsi.2022.02.041
• Languages: English
• ISSNs: 1050-4648

Abstract

Abstract: Infectious spleen and kidney necrosis virus (ISKNV), the type species of the genus Megalocytivirus, infects a variety of teleost fish species and causes substantial losses in the aquaculture industry worldwide. ISKNV ORF71L is 1611 bp in length, encodes a 537-amino-acid peptide and was previously identified as a viral structural protein in the ISKNV virion. In this study, the ORF71L deletion mutant virus strain ISKNV-Δ71 was obtained through a homologous recombination approach. The multistep growth curves showed that ISKNV-Δ71 replication was faster than ISKNV-WT replication in mandarin fish fry cells (MFF-1 cells) before 48 h post-infection (hpi). The cumulative mortality of ISKNV-Δ71-infected mandarin fish ( Siniperca chuatsi ) was lower than that of fish infected with ISKNV-WT. The copy numbers of viral genome equivalents (GEs) in ISKNV-Δ71-infected mandarin fish spleens were also lower than those in ISKNV-WT-infected spleens. Deletion of ORF71L resulted in ISKNV virulence attenuation in mandarin fish. Furthermore, we found that the number of melanomacrophage centers (MMCs) in ISKNV-Δ71-infected mandarin fish spleens was higher than that in ISKNV-WT-infected mandarin fish spleens. Transcriptomic analysis showed that the cytokine–cytokine receptor interaction pathway had the most significant change between ISKNV-Δ71- and ISKNV-WT-infected MFF-1 cells. These results indicated ORF71L is a virulence-related gene of ISKNV. ORF71L could be considered as a potential target for the development of engineered attenuated live vaccines via multigene deletion or as a potential insertion site for exogenous protein expression. Highlights: ORF71L deletion mutant strain of ISKNV (ISKNV-Δ71) was obtained through a homologous recombination approach. ISKNV-Δ71 replication was faster than ISKNV-WT in MFF-1 cells. ISKNV ORF71L was a virulence-related gene. The expression of cxcl12a was upregulated in ISKNV-Δ71-infected liver and spleen compared with those by ISKNV-WT.