Abstract
Channel catfish (Ictalurus punctatus) is an important agricultural fish that has been plagued by Streptococcus iniae (S. iniae) infections in recent years, some of them severe. C5a peptidase is an important virulent factor of S. iniae. In this study, the subunit vaccine containing the truncated part of C5a peptidase (pSCPI) was mixed with aluminum hydroxide gel (AH), propolis adjuvant (PA), and Freund’s Incomplete Adjuvant (FIA). The immunogenicity of the pSCPI was detected by Western-blot in vitro. The relative percent survival (RPS), lysozyme activity, antibody titers, and the expression of the related immune genes were monitored in vivo to evaluate the immune effects of the three different adjuvants. The results showed that pSCPI exerted moderate immune protection (RPS = 46.43%), whereas each of the three adjuvants improved the immune protection of pSCPI. The immunoprotection of pSCPI + AH, pSCPI + PA, and pSCPI + FIA was characterized by RPS values of 67.86%, 75.00% and, 85.71%, respectively. Further, each of the three different adjuvanted pSCPIs stimulated higher levels of lysozyme activity and antibody titers than the unadjuvanted pSCPI and/or PBS buffer. In addition, pSCPI + FIA and pSCPI + PA induced expression of the related immune genes under investigation, which was substantially higher than the levels stimulated by PBS. pSCPI + AH significantly stimulated the induction of MHC II β, CD4-L2, and IFN-γ, while it induced slightly higher production of TNF-α and even led to a decrease in the levels of IL-1β, MHC I α, and CD8 α. Therefore, we conclude that compared with the other two adjuvants, FIA combined with pSCPI is a more promising candidate adjuvant against S. iniae in channel catfish.
Highlights
Channel catfish (Ictalurus punctatus) is an important agricultural fish, especially in China where its yield was 150,000 tons in 2008 [1,2]
A specific band of approximately 87 KDa was determined in the rabbit anti-pSCPI experimental group, which was missing in the negative group (Figure 1, lanes 1 and 2)
The results showed that pSCPI possessed immunogenicity
Summary
Channel catfish (Ictalurus punctatus) is an important agricultural fish, especially in China where its yield was 150,000 tons in 2008 [1,2]. S. iniae, a β-hemolytic Streptococcus species, has been an important fish pathogen with a broad host range, such as the hybrid striped bass (Morone chrysops M saxatilis), tilapia (Oreochromis spp.), flounder (Paralichthys dentatus), rainbow trout (Oncorhynchus mykiss), channel catfish, and salmon (Salmo salar) [5,6,7,8]. This Gram-positive coccus causes disease in human [6,9]. Propolis is a natural product, exhibiting immunomodulatory, anti-inflammatory, antimicrobial, antitumor, antioxidant, antiviral, antiparasitic, and anti-diabetic activities [22], due to which it is regarded as a potential adjuvant in veterinary vaccines
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