Transcriptome analysis reveals similarities and differences in immune responses in the head and trunk kidneys of yellow catfish (Pelteobagrus fulvidraco) stimulated with Aeromonas hydrophila

Teleosts have a unique immune system because their head kidney (HK) and trunk kidney (TK) are sites for hematopoiesis. However, the immune functions of the HK and TKs require further elucidation in yellow catfish (Pelteobagrus fulvidraco). In the present study, imprints of the HK and TK were examined using the Wright's-Giemsa staining method. Morphological characteristics of the blood cell lineages revealed that the HK and TK were hematopoietic organs. To explore its immune function, transcriptome sequencing was performed after infection with Aeromonas hydrophila. A total of 1139 genes showed significant alterations in their expression in the kidney; these genes included 737 upregulated and 402 downregulated genes. Furthermore, 1117 differentially expressed genes were observed in the HK, which included 784 upregulated and 333 downregulated genes. Both organs showed 357 upregulated genes and 85 downregulated genes. Some immune-related genes were only expressed in the TK, such as ATP-dependent RNA helicase DDX58, the gene encoding the immunoglobulin heavy chain and light chain. The immune responses in the HK and TK were differential and the TK played a critical role in the mechanism underlying the immune response. The purpose of the present study was to facilitate the elucidation of the immune defense mechanism of yellow catfish and other teleosts.