The Dynamic Immune Response of Yellow Catfish (Pelteobagrus fulvidraco) Infected With Edwardsiella ictaluri Presenting the Inflammation Process

Abstract

Edwardsiella ictaluri is a highly destructive pathogen in cultured yellow catfish, thus it was very necessary to study the immune response of yellow catfish against bacterial infection. In this study, RNA-Seq technology was used to study the immune response in two distinct tissues of yellow catfish at eight different time points (h) after E. ictaluri infection. The number of differentially expressed genes (DEGs) in the spleen and liver was low at 3 h and 6 h post-infection, respectively. Afterwards, the most number of DEGs in the spleen was detected at 72 h, while the number of DEGs in the liver maintained a high level from 24 h to 120 h. The GO and KEGG enrichment analyses of DEGs at different time points uncovered that cytokines were continuously transcribed at 6 h to 120 h; whereas the liver is the main organ that secretes the components of the complement system, and metabolic regulation was activated from 12 h to 120 h. Moreover, an overview of the inflammation response of yellow catfish was exhibited including pattern-recognition receptors, inflammatory cytokines, chemokines, complements, and inflammation-related signal pathways. The similar expression tendency of nine genes by qRT-PCR validated the accuracy of transcriptome analyses. The different transcriptomic profiles obtained from the spleen and liver will help to better understand the dynamic immune response of fish against bacterial infection, and will provide basic information for establishing effective measures to prevent and control diseases in fish.

Keywords: Edwardsiella ictaluri; bacteria; inflammation; transcriptome; yellow catfish.

Figure 1

The 15 most enriched GO terms in the spleen of yellow catfish at different time points following E. ictaluri challenge. I: biological process, II: cellular component, III: molecular function.

Figure 2

The 15 most enriched GO terms in the liver of yellow catfish at different time points following E. ictaluri challenge. I: biological process, II: cellular component, III: molecular function.

Figure 3

The DEGs of pattern-recognition receptor in yellow catfish after E. ictaluri infection. (A, B): The DEGs identified in the spleen and liver, respectively. The DEGs of pattern-recognition receptor were analyzed at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 120 h post-infection in the spleen and liver. The color gradient represents highly up-regulated (red) to highly down-regulated (white) genes. Significant differences at different time points post-infection compared to the control (0 h) are indicated by asterisks (*P < 0.05). (C): Structural features of pattern-recognition receptor DEGs in yellow catfish. The domain organizations were predicted by the SMART online server.

Figure 4

The DEGs of chemokine in yellow catfish after E. ictaluri infection. (A, B): The DEGs identified in the spleen and liver, respectively. The DEGs of chemokine were analyzed at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 120 h post-infection in the spleen and liver. The color gradient represents highly up-regulated (red) to highly down-regulated (white) genes. Significant differences at different time points post-infection compared to the control (0 h) are indicated by asterisks (*P < 0.05). (C, D): Multiple alignments of the deduced amino acid sequences of detected CXCLs and CCLs, respectively. The amino acid sequences of these genes were predicted using MEGA 6.06. ClustalW program in MEGA 6.06 and BoxShade were used for multiple sequence alignments. Similar amino acid residues are marked as grey shadow and identical residues as black shadow. Absent amino acids are indicated by dashes (-). (E): Structural features of chemokine receptor DEGs in yellow catfish. The domain organizations were predicted by the SMART online server.

Figure 5

The DEGs of inflammatory cytokine in yellow catfish after E. ictaluri infection. (A, B): The DEGs identified in the spleen and liver, respectively. The DEGs of inflammatory cytokine were analyzed at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h and 120 h post-infection in the spleen and liver. The color gradient represents highly up-regulated (red) to highly down-regulated (white) genes. Significant differences at different time points post-infection compared to the control (0 h) are indicated by asterisks (*P < 0.05). (C): Structural features of inflammatory cytokine DEGs in yellow catfish. The domain organizations were predicted by the SMART online server.

Figure 6

The DEGs of complement in yellow catfish after E. ictaluri infection. (A, B): The DEGs identified in the spleen and liver, respectively. The DEGs of complement were analyzed at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 120 h post-infection in the spleen and liver. The color gradient represents highly up-regulated (red) to highly down-regulated (white) genes. Significant differences at different time points post-infection compared to the control (0 h) are indicated by asterisks (*P < 0.05). (C): Structural features of complement DEGs in yellow catfish. The domain organizations were predicted by the SMART online server.

Figure 7

The DEGs of adaptor molecule in yellow catfish after E. ictaluri infection. (A, B): The DEGs identified in the spleen and liver, respectively. The DEGs of adaptor molecule were analyzed at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 120 h post-infection in the spleen and liver. The color gradient represents highly up-regulated (red) to highly down-regulated (white) genes. Significant differences at different time points post-infection compared to the control (0 h) are indicated by asterisks (*P < 0.05). (C): Structural features of adaptor molecule DEGs in yellow catfish. The domain organizations were predicted by the SMART online server.

Figure 8

Comparison of the expression profiles of eight DEGs determined by Illumina HiSeq™ 2000 sequencing platform and qRT-PCR at 3 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 120 h post-infection. Data shown are the mean of triplicates ± SD. (A): Spleen, (B): Liver.

Figure 9

A graphic overview of the inflammation response of yellow catfish.