β-glucan alleviates the immunosuppressive effects of oxytetracycline on the non-specific immune responses and resistance against Vibrio alginolyticus infection in Epinephelus fuscoguttatus × Epinephelus lanceolatus hybrids

We evaluated the effectiveness of vitamin C and Aeromonas salmonicida vaccine in grouper (Epinephelus fuscoguttatus) for increasing immune responses and protection against A .salmonicida. The vitamin C used was polyethoxylated ascorbic and tocopherol. The vaccine was prepared from formalin-killed cells and concentrated extracellular products of a single isolate A. salmonicida. Bath immersion vitamin C and vaccine trials were conducted for 60 min. Fish used had a mean weight 25 g. Control groupers were injected with tryptic soy broth. The results showed that vitamin C enhanced phagocytic activity in head kidney leucocytes of grouper 7, 14, 28 and 36 days after treatments. A significant different of the antibody titre was found between control fish and the treated fish at 42 days after treatments. In addition, at day 42, Relative Percent Survival (RPS) for control group was 53.3 %, vitamin C-treated group was 80.0 % and vaccinated group was 90.0 %. The results of this study suggest that bath immersion of vitamin C provided an increasing of phagocytic activity (non-specific immune responses), titre antibody (specific immune responses) and protection against A. salmonicida infection in grouper. A. salmonicida vaccine also en-hanced titre antibody and protection against A. salmonicida infection in grouper.

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Expression analysis and tissue localization of IgZ in the grouper Epinephelus coioides after Vibrio alginolyticus infection and vaccination

10.21203/rs.3.rs-386343/v1 ◽

2021 ◽

Author(s):

Yao-Wu Fu ◽

Zhan-Juan Yao ◽

Miao Cui ◽

Qi-Zhong Zhang

Keyword(s):

Immune Responses ◽

Bacterial Pathogen ◽

Head Kidney ◽

Vibrio Alginolyticus ◽

Economic Losses ◽

Epinephelus Coioides ◽

Farmed Fish ◽

Transcriptional Changes

Abstract Background The orange-spotted grouper (Epinephelus coioides) is an important marine farmed fish in China. It is affected by the bacterial pathogen Vibrio alginolyticus, which causes high mortality and substantial economic losses. Results We studied the transcriptional changes of the IgZ gene in E. coioides following V. alginolyticus stimulation and investigated the distribution of IgZ in different tissues. The highest expression level of IgZ occurred in the head kidney. When fish were exposed to live and inactivated V. alginolyticus, the expression levels of IgZ in head kidney, spleen, intestine, gill, and blood cell were significantly upregulated. In an in situ hybridization study, IgZ mRNA-positive cells were detected in head kidney, spleen, and gill, but positive signals were not detected in liver and intestine. IgZ-labeled cells increased in the head kidney, spleen, and gill post-infection with V. alginolyticus for 21 days. Conclusions The present study provided additional evidence that IgZ was involved in mucosal immune responses against pathogens. These results help explain the role of IgZ in E. coioides defense against V. alginolyticus infection.

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