Early Insights on How Fish Immune Systems Fight Viral Infections

Jenn Hoskins
25th July, 2024

Early Insights on How Fish Immune Systems Fight Viral Infections

Grass Carp (Ctenopharyngodon idella)

Photo adapted from: Aalbert Rebergen / CC BY (Source)

Key Findings

  • Researchers at Hunan Agricultural University studied the immune response of grass carp to Grass Carp Reovirus (GCRV) infection
  • The study found that the mRNA levels of BF/C2A and BF/C2B in grass carp increased with GCRV replication, indicating their role in the immune response
  • Excessive inflammation and high BF/C2 mRNA levels coincided with peak GCRV replication, suggesting that hyperactivation of the complement system can lead to severe inflammation and tissue injury
Grass carp reovirus (GCRV) infection poses a significant threat to aquaculture, causing high mortality rates in grass carp. Understanding the immune response mechanisms in grass carp is crucial for developing effective treatments and preventive measures. A recent study by researchers at Hunan Agricultural University sheds light on the role of BF/C2, a critical molecule in the coagulation complement cascade pathway, in the immune response of grass carp during GCRV infection[1]. The complement system, a pivotal component of the innate immune system, helps defend against microbial infections and clear immune complexes and injured cells[2]. In mammals, the complement system includes various pathways such as the classical, alternative, and lectin pathways. Previous research has shown that bony fish, like teleosts, possess almost all orthologues of mammalian complement components, except for some regulatory proteins and receptors[3]. Additionally, the complement system in fish is more diversified, with multiple isoforms of certain components, which may indicate functional divergence[3]. BF/C2 in grass carp is analogous to mammalian complement components and is involved in the classical, alternative, and lectin pathways. The study conducted in vivo experiments demonstrating that the mRNA expression levels of BF/C2 (A, B) in grass carp positively correlated with GCRV viral replication at various stages of infection. This correlation suggests that BF/C2 plays a significant role in the immune response to GCRV infection. The researchers observed that excessive inflammation, leading to death, coincided with peak levels of BF/C2 (A, B) mRNA expression and GCRV viral replication. This finding is consistent with previous studies indicating that hyperactivation of the complement system can drive severe inflammatory responses, potentially leading to tissue injury[2]. The susceptibility of the kidney to complement-mediated injury in mammals is well-documented, and similar mechanisms may be at play in grass carp, affecting multiple organs during GCRV infection[2]. To further investigate the role of BF/C2, the researchers conducted transcriptome sequencing analysis at critical time points (3 hours and 9 hours post-infection). They identified significant differences in the expression of BF/C2A and BF/C2B during different stages of CIK (carp kidney cell line) infection with GCRV compared to the control group. Specifically, the BF/C2A_3 and BF/C2A_9 groups exhibited 2729 and 2228 differentially expressed genes (DEGs), respectively, while the BF/C2B_3 and BF/C2B_9 groups showed 2303 and 1547 DEGs, respectively. KEGG functional enrichment analysis of these DEGs revealed shared pathways between BF/C2A and the control group, including the C-type lectin receptor signaling pathway, protein processing in the endoplasmic reticulum, Toll-like receptor signaling pathway, Salmonella infection, apoptosis, tight junction, and adipocytokine signaling pathway. These pathways are crucial for immune response and cellular processes, indicating that BF/C2A influences various aspects of the immune response to GCRV infection. Similarly, the BF/C2B groups at 3 and 9 hours shared pathways related to protein processing in the endoplasmic reticulum, glycolysis/gluconeogenesis, and biosynthesis of amino acids. These pathways are essential for cellular metabolism and protein synthesis, suggesting that BF/C2B also plays a vital role in the immune response and cellular functions during GCRV infection. The study validated the mRNA levels of these DEGs in cellular models, confirming consistency with the sequencing results. Additionally, the mRNA expression levels of candidate genes (such as mapk1, il1b, rela, nfkbiab, akt3a, hyou1, hsp90b1, dnajc3a) in the head kidney, kidney, liver, and spleen of grass carp immune tissue were significantly different from those of the control group following BF/C2 (A, B) protein injection in vivo. These genes play essential roles in the immune response, further confirming the involvement of BF/C2 in coping with GCRV infection. The findings of this study contribute to the growing body of knowledge on the complement system in fish, particularly teleosts, and its role in immune responses[3][4]. The identification of BF/C2 as a critical molecule in the coagulation complement cascade pathway provides valuable insights into the immune mechanisms of grass carp and highlights potential targets for therapeutic intervention in GCRV infection.

GeneticsBiochemAnimal Science

References

Main Study

1) Preliminary study of BF/C2 on immune mechanism of grass carp against GCRV infection

Published 24th July, 2024

https://doi.org/10.1186/s12864-024-10609-3

Related Studies

2) Overview of complement activation and regulation.

https://doi.org/10.1016/j.semnephrol.2013.08.001

3) The complement system in teleost fish: progress of post-homolog-hunting researches.

https://doi.org/10.1016/j.dci.2011.03.003

4) Complement system of bony and cartilaginous fish.

Journal: Fish & shellfish immunology, Issue: Vol 10, Issue 3, Apr 2000


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