TRANSCRIPTOMIC ANALYSIS OF XENOGENEIC IMMUNE REJECTION IN <italic>HYDRA</italic>

To investigate the molecular mechanisms of xenogeneic immune rejection in Hydra, we developed a novel grafting method using elongated conical toothbrush bristles as carriers to connect two polyp body segments. Successful chimeras were generated through homografts (between head-removed aposymbiotic and tail-removed symbiotic strain of Hydra sinensis) and xenografts (between head-removed Hydra vulgaris and tail-removed symbiotic strain of Hydra sinensis). Post-transplantation monitoring revealed significant immune rejection in xenograft chimeras: over 60% maintained structural integrity at 12h, ~40% at 24h, PHydra: Xenotransplantation activates innate immunity, ferroptosis, and apoptosis, with the latter two processes modulating the intensity of innate immune responses. Activated innate immunity triggers metabolic reprogramming in immune cells and initiates antigen processing and presentation, suggesting activation of a primordial acquired immune mechanism. However, no evidence supported direct involvement of an acquired immune system in xenogeneic rejection. Thus, xenogeneic immune rejection in Hydra primarily results from innate immune responses and metabolic reprogramming of immune cells. This study provides fundamental data for understanding cellular and molecular mechanisms of xenogeneic immune rejection in animals.