Abstract: Objective: To investigate the effect of fucoidan from Laminaria japonica on immune regulation in immunodepressed mice by oral administration. Methods: In this study, different fucoidan fractions were obtained by acid hydrolysis, anion exchange chromatography on Q-Sepharose FF and free radical oxygen degradation and ultrafiltration technology from high molecular weight fucoidan extracted from Laminaria japonica. The fractions with higher sulfate ester and fucose content on immune regulation were selected by chemical analysis. KM mice were randomly divided into twelve groups: normal control group, model control group, positive group, low dosage (25 mg/(kg·d)), medium dosage (50 mg/(kg·d)) and high dosage (100 mg/(kg·d)) groups of F-2, Fa and Fb fractions, respectively. The immune regulation was investigated by using the model mice in normal and in immunodepression induced by hydrocortisone. Results: The effect on immune function of mice administered with different fucoidan fractions from Laminaria japonica did not reveal significant difference. All F-2, Fa and Fb could antagonize the decline of spleen/body weight induced by hydrocortisone, increase hemolysin content (HC50), and promote the ability of macrophages for celiac macrophage. Meanwhile, both F-2 and Fa could improve delayed hypersensitivity level, while Fb had no significant effect on delayed hypersensitivity level. Conclusion: Fucoidan fraction had an excellent effect on immune regulation in immunodepressed mice. However, these fractions did not reveal significant difference in the effect on immune function of mice.

Key words: fucoidan, immunodepressed mice, immune regulation