A3α-peptidoglycan extracted fromBifidobacteriumsp. could enhance immunological ability ofApostichopus japonicus

Abstract

To assess the effects of A3α-peptidoglycan (A3α-PG) extracted from Bifidobacterium sp. on the immune response and disease resistance of sea cucumber, different concentrations (0, 0.5, 5 and 50 mg mL−1) of A3α-PG suspensions were used to perform hypodermic injection on Apostichopus japonicus, followed by a Vibrio splendidus challenge. Total coelomocyte count (TCC), phagocytosis activity and activities of four immunological enzymes in both cell-free coelomic fluid (extra-cellular, EC) and coelomocyte lysate supernatant (intracellular, IC), including acid phosphatase (ACP), alkaline phosphatase (ALP), superoxide dismutase (SOD) and peroxidase (POD), were measured at 2, 6, 14 and 24 h post injection (hpi). The TCC was not significantly affected (P > 0.05) by A3α-PG, ranging from 1.84 × 106 to 3.53 × 106 cells mL−1. The coelomocyte phagocytosis activity was significantly activated (P < 0.05) in all the A3α-PG treatments, whereas no significant difference was observed between them except 24 hpi (P > 0.05). The EC-ACP activity in the 5.0 mg mL−1 treatment increased significantly (P < 0.05) at all sampling times, while the IC-ACP activity in the 50 mg mL−1 treatment increased significantly (P < 0.05) at 2 hpi. Also, the 5.0 mg mL−1 treatment had significant (P < 0.05) increase in the EC-ALP activity within 14 hpi and the EC-POD activity at 2 hpi, respectively, while significantly (P < 0.05) enhanced IC-ALP and IC-POD activities were observed in the 50 mg mL−1 treatment within 6 hpi and at 2 hpi, respectively. Only the 5.0 mg mL−1 treatment showed significant (P < 0.05) increase in the EC-SOD activity at 2 hpi and IC-SOD activity within 14 hpi, respectively. The challenge test showed that the animals treated with 50 mg mL−1 of A3α-PG had notably lower cumulative mortality after 14 days following V. splendidus exposure. All together, these results suggest that A3α-PG could positively enhance immune response that effectively promotes the health status of A. japonicus against V. splendidus infection.