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

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.