Various studies have highlighted the ability of CpG oligodeoxynucleotides (ODN CpG) to strengthen immunity in mammals.
Previous studies have shown that oral administration of CpG ODNs reduces the mortality rate of shrimp exposed to white spot syndrome virus. However, it is not clear how CpG oligodeoxynucleotides affect the intestines of shrimp.
A team of researchers from the Ocean University of China, Hainan Yazhou Bay Seed Laboratory, and the Center for Marine Molecular Biotechnology synthesized and added 17 types of CpG oligodeoxynucleotides (A, B, C, P, N) to the feed of Litopenaeus vannamei shrimp. They evaluated the variation of the intestinal flora in shrimp through 16S rDNA sequencing.
CpG Oligodeoxynucleotides
The authors of the study state that CpG oligonucleotides (CpG-ODN) are short synthetic DNA with a CpG motif that mimics bacterial genomic DNA and are potent activators of both adaptive and innate immunity.
CpG-ODNs are generally classified into four classes: A, B, C, and P, based on their structural differences, and each class of CpG oligonucleotides exhibits different immunostimulatory and immunomodulatory effects.
There have been various experiments using CpG-ODNs to enhance the immunity of Japanese flounder (Paralichthys olivaceus) and rainbow trout (Oncorhynchus mykiss). However, it is not clear how CpG oligonucleotides affect the intestines of shrimp.
Immunoprotective effects of CpG-ODN
The immunoprotective effects of CpG oligonucleotides stimulate immune cells and trigger immune responses to infections in many vertebrate species, including humans, sheep, mice, birds, and teleost fish.
“In this study, different types of CpG ODNs produced divergent immunostimulatory effects due to their sequence divergence. Specifically, they increased the expression of genes related to innate immunity, improved antioxidant capacity in the hepatopancreas, and enhanced the structure of the intestinal flora,” they reported.
Furthermore, they highlighted the expression profiles of genes related to the immune system, including IL-1β, IL-8, IL-10, TNF-α, ALF, and TOR in L. vannamei shrimp fed with CpG 1826, CpG 1681, CpG 2006, CpG 8954, CpG M362, CpG 1585, and CpG 2143, showing significant upregulation.
“The high expression of TNF-α and ALF in this study was consistent with previous studies, suggesting that the immunity of shrimp was significantly increased as a result of oral administration of CpG ODNs,” the researchers said.
Antioxidant capacity of hepatopancreas
According to the study, the increase in antioxidant capacity in the hepatopancreas of L. vannamei illustrated that partial CpG ODNs could not only function at the genetic level but also affect protein expression.
It is known that the activity of antioxidant enzymes, including GST, CAT, GPX, and SOD, plays an important role in the innate immune system due to the absence of acquired immunity in L. vannamei.
“The group of effective CpG-ODNs in the study showed a close disposition of tubules, a complete structure of the basal membrane, and a regular lumen shape, which improved the antioxidant properties of the hepatopancreas, led to the repair of hepatopancreas damage, and maintained normal tissue and function,” they reported.
Conclusion
“The present study showed that various dietary CpG ODNs can improve intestinal health and immunity in shrimp without adverse effects, including CpG 2395, CpG 1585, CpG 1681, CpG 8954, CpG 2143, CpG 21424, CpG 21425, CpG 21426, CpG 2429, CpG 2216, and CpG M362,” the researchers conclude.
They further conclude that the improvement encompassed genes related to the immune system, antioxidant enzymes, and intestinal microbial diversity.
“The study results indicate the potential application of CpG ODNs in enhancing shrimp immunity and lay the foundation for further research on their molecular series,” they concluded.
The study was funded by the Key Research and Development Program of Shandong Province, the National Key Research and Development Program of China, the Project of Sanya Yazhou Bay Science and Technology City Management Foundation, the Hainan Provincial Joint Project of Sanya Yazhou Bay Science and Technology City, and the Startup Fund of Young Talents Project of Ocean University of China/Fundamental Research Funds for the Central Universities.
Reference (open access)
Hu, F., Wang, Y., Hu, J., Bao, Z., & Wang, M. (2023). Comparative study of the impact of dietary supplementation with different types of CpG oligodeoxynucleotides (CpG ODNs) on enhancing intestinal microbiota diversity, antioxidant capacity, and immune-related gene expression profiles in Pacific white shrimp (Litopenaeus vannamei). Frontiers in Immunology, 14.
