Comparative transcriptomic analysis of the thymus and other immune-related tissues using post-mortem samples from stranded cetaceans in South Korea.

Cetaceans are mammals that have adapted to aquatic environments, but their immunological characteristics are not well understood. In this study, we performed comparative transcriptomic analyses of major immune-related tissues (thymus, spleen, liver, and kidney) from post-mortem samples of stranded cetaceans in Korea, including the finless porpoise, fetal minke whale and Risso's dolphin. For cross-taxa comparisons, we retrieved publicly available transcriptomic datasets from terrestrial mammals (human and mouse), teleosts (zebrafish, common carp, and turbot), birds (chicken), reptiles (green sea turtle and loggerhead sea turtle), and cartilaginous fish (shark). We analyzed immune-related gene expression patterns using a unified KEGG-based annotation framework. Despite the post-mortem nature of the samples, tissue-specific transcriptional characteristics were maintained, with the thymus showing the widest variety of immune-related genes. Consequently, our comparative transcriptomic analyses focused on thymic tissues across the different animal taxa. We found that pathways related to antigen processing and presentation, as well as T cell receptor signaling, were relatively downregulated. In contrast, the complement/coagulation cascades and platelet activation pathways exhibited more prominent transcriptional representation. Within the complement system, components of the lectin and alternative pathways were more pronounced than those of the classical pathway, which may be associated with constant exposure to diverse waterborne microorganisms inherent to mammalian life in aquatic environments. These findings highlight immune-physiological features relevant to mammalian life in aquatic environments and lay the groundwork for future standardized comparative studies.