Uptake dynamics and intracellular distribution of fluorescein-labeled chitosan oligosaccharide in coelomocytes of Apostichopus japonicus.

Chitooligosaccharides (COS) has shown promising potential in enhancing the immunoprotective effects of Apostichopus japonicus. However, its intracellular distribution in within the coelomocytes of this species remains unclear. In this study, using fluorescein isothiocyanate (FITC) labeled COS technology combined with fluorescence microscopy and a microplate detection system, the uptake kinetics and subcellular distribution of FITC-COS in five types of coelomocytes (amoebocytes, fusiform cells, lymphocytes, hyaline cells and spherulocytes) were analyzed. The results indicate that the cellular uptake of FITC-COS was time- and dose-dependent, and exhibits distinct distribution patterns across various cell types: diffuse distribution in spherulocyte, polar distribution in fusiform cell, and early perinuclear punctate aggregation in lymphocytes. In all cell types, FITC-COS does not enter the nucleus. This study reveals the dynamic distribution patterns of COS in the immune cells of Apostichopus japonicus, providing cytological evidence for elucidating its immune-enhancing mechanisms and theoretical support for the development of COS as an aquatic immunostimulant. However, this study did not conduct co-localization experiments of COS with specific organelles, and its exact intracellular target remains to be further verified.