Abstract / Summary
As non-chordate deuterostomes, echinoderms constitute a key phylum for comparative immunology studies related to vertebrates. Among them, sea cucumbers (Holothuroidea) have attracted growing scientific interest, both for aquaculture applications and for their potential as sources of bioactive compounds. Over the past decades, research on the sea cucumber immune system—especially on immune-related genes—has expanded considerably. This progress has been largely driven by efforts to improve the health and disease resistance of the aquacultured species Apostichopus japonicus . In contrast, cellular immunology has received comparatively less attention, and modern molecular approaches have rarely been applied to investigate the functions of sea cucumber immune cells, known as coelomocytes. Although numerous coelomocyte types have been described over the last century, their classification still solely relies on morphological criteria, which likely masks an important functional diversity within these cell populations. This review compiles the current knowledge on both the molecular and cellular components of the sea cucumber immune system, thereby highlighting the existing gaps between these two levels of investigation. The principal immune mechanisms are presented together with their associated molecular and cellular actors. In addition, recent advances linking molecular and cellular immunity are discussed, and future directions are also proposed for the molecular characterisation of coelomocytes at single-cell-type resolution. Overall, this review provides a framework for bridging molecular and cellular immunology in sea cucumbers—two fields that remain largely disconnected—and offers an updated overview of immune components in these economically and ecologically important marine invertebrates.