Immune Response and Protective Efficacy of β-Glucan and Alkoxyglycerol as Adjuvant in Streptococcus agalactiae Formalin-Inactivated Vaccine in Nile Tilapia (Oreochromis niloticus).

Abstract

Nile tilapia (Oreochromis niloticus) farms face streptococcus agalactiae infections causing mass mortality following economic losses. To date, no commercial fish vaccine is available in India to protect against streptococcosis due to a lack of proper adjuvants and vaccine targets. Multiple studies justify that immunomodulators like β-glucan and Alkoxy glycerol (AKG) have improved immunity in fish. β-glucan and AKG are natural homopolymers and lipids, respectively, which have proven immunostimulant capabilities in fish and can be effectively used as a prominent adjuvant to improve vaccine efficacy. The present study aims to demonstrate the improved adjuvant efficacy of the formalin-inactivated S. agalactiae vaccine. Nile tilapia fingerlings were immunised with formalin-inactivated S. agalactiae vaccines mixed with β-glucan and AKG. Each week postvaccination, the serum nonspecific responses were measured by lysozyme, myeloperoxidase, SOD and bactericidal activity. Following the challenge after 28 days postvaccination, the survival rate achieved was 32.14%, 57.14%, 53.57% and 71.43% in the respective experimental groups. The immune gene expressions of IgM, TCRβ and MHCII were evoked postvaccination. The specific serum IgM titre values were significantly upregulated in 14- and 28-day postvaccinated experimental groups. The study highlights the enhanced activity of β-glucan and AKG incorporated vaccine, which has the potency towards commercialisation for sustainable aquaculture.