Comprehensive transcriptome profiling and functional analysis of the meagre (Argyrosomus regius) immune system

Meagre (Argyrosomus regius) belongs to the family Sciaenidae and is a promising candidate for Mediterranean aquaculture diversifcation. As a relatively recent species in aquaculture, the physiological consequences of the immune system activation in meagre are understudied. Spleen, as a primary lymphoid organ has an essential role in meagre immune and inflammatory responses. In this study, we have evaluated the in vivo effects of lipopolysaccharide (LPS) on the spleen transcriptome of meagre by RNA-seq analysis at 4 and 24 h after injection. The assembled transcripts were assigned to immunological processes. At 24 h, the number and type of differential immune-related genes regulated by LPS was higher than at 4 h. However, at 4 h the upregulation of immune-related genes was greater. Several genes related to the innate immune response were upregulated including tolllike receptor 5, and multiple interferons and interferon-related proteins. In the present work, it was shown that several chemokines and chemokine ligands (e.g. cxcl10, ccl21) as well as cytokines (e.g. il1b, il12, il27) were overexpressed as a result of LPS injection, supporting their role as mediators of the innate and adaptive immune response. KEGG analysis found that LPS-stimulated immune responses mainly involve cytokine and protein-protein interactions involved in pathogen response. Specifcally, genes involved in the MHCI and MHCII pathways were induced as early as 4 h post LPS injection. These results will help to understand the pathogenesis and host defense system in meagre. Individual juvenile fish (22 g) of meagre (Argyrosomus regius) were divided into two groups and injected intraperitoneally with 10 μg/g fsh of lipopolysaccharides (LPS) extracted from Photobacterium damselae subsp. piscicida Lg41/01 or phosphate buffer saline (PBS). The spleen was removed from 12 fish pooled into 3 groups of 4 fish for each sampling point (4 and 24 h), both from PBS treated fish (control samples) and LPS treated fsh (experimental samples) at 4 h and 24 h after treatment [n = 3 (pools, 4 fish/pool)/treatment/sampling point)]