Allograft inflammatory factor-1 (AIF-1) is an interferon (IFN)-γ-inducible Ca2+-binding cytokine that forms an important part of immune defence and the inflammation response. AIF-1 expressed by the gene AjAIF-1 has a crucial role in defending against pathogens from physical injury or infection. AIF-1 is part of the intracellular calcium-binding protein family and is widespread with homologs in vertebrates and invertebrates. The isolated and identified AIF-1 from A. japonicus is similar to those found in humans, sea urchins and abalone.This study by Ji et al., (2014) is the first to clone, characterise, and identify the distribution and temporal expression of AjAIF-1 after bacterial exposure and tissue damage in A. japonicus. Vibrio splendidus is known to cause skin ulceration syndrome in A. japonicus so was used to test and stimulate the immune response of the sea cucumber.
Healthy animals were collected from a sea cucumber farm in Dalian, China. The bacterial challenge experiments were conducted by injecting 100 μL (1 x 107 CFU ml-1) of V. splendidus in PBS into individual animals. Control groups were injected with just 100 μL of PBS. After infection, individuals were sampled at 2, 4, 8, 12, 24 and 48 hours. For the physical injury experiment, a dorsal papilla was cut in the middle of the sea cucumber, in the same location for each individual. The control group comprised of uninjured animals. Again, individuals were sampled at 2, 4, 8, 12, 24 and 48 hours post injury. The AjAIF-1 gene was cloned from cDNA and analysed with quantitative real time PCR (qRT-PCR) to ascertain the level of mRNA expression of AjAIF-1 in the various tissues of the sea cucumbers and determine immune responses.
This study found that AjAIF-1
was expressed in a range of tissues, including the body wall and muscle,
respiratory tree, tube feet, intestine and coelomocytes. Highest expression was
in the respiratory tree, followed by the tube feet. Despite being an internal
organ, the respiratory tree is in constant contact with the water and with
potential pathogenic microorganisms. The authors did not comment on why AjAIF-1 was expressed highly in the tube
feet. Perhaps tube feet may be prone to damage and bacterial infection
generally but especially so during handling at sea cucumber farms.
AjAIF-1
transcripts were upregulated markedly in coelomocytes following exposure to V. splendidus. Coelomocytes are a
crucial part of the echinoderm immune system and have a role in both
eliminating pathogens and producing humoral protective factors. High expression
of AjAIF-1 therefore makes reasonable
sense. This showed that AjAIF-1 not
only responds to an invading pathogen but is an important part of the inflammatory
response. Expression levels of AjAIF-1 transcripts
peaked 4 hours after bacterial exposure, particularly in coelomocytes after
papilla injury. This early inflammatory response indicates that it assists in wound
healing.
Interestingly, 24 and 48 hours after infection, AjAIF-1 levels of expression were lower
than the control group. This has important implications for the treatment of
sea cucumbers after injury or bacterial infection as the host defence response
appears to be lower than pre-infection levels. This study is invaluable for
understanding not only the role of AjAIF-1
upregulation in holothurian immune systems but also the greater need for protecting
A. japonicus from disease and injury
in aquaculture. It may also offer insights into the immunity of other
invertebrates, particularly those that are farmed commercially.
Reference: Ji, N., Chang, Y., Zhao, C., Pang, Z. and He,
Z. (2014) Cloning and gene expression of allograft inflammatory factor-1
(AIF-1) provide new insights into injury and bacteria response of the sea
cucumber Apostichopus japonicus (Selenka,
1867), Fish & Shellfish Immunology,
38, 400-405.
Hi Anita,
ReplyDeleteDid the authors say the site of injection of the Vibrio? Would the immune response vary do you think, depending on where the pathogen first infects the sea cucumber? Similarly in us when the body first locates the pathogen and then works to eliminate it, could there be a reduced immune/inflammation response say if the injection site were further away from the coelomocyte region (if there is a region!)?
Thank you! :)
Bekki
Hi Bekki
ReplyDeleteThanks, these are some good questions. The Vibrio was injected into the coelomic cavity in the sea cucumbers as the coelomocytes are the main component of an echinoderm immune system.
Immune responses after tissue injury or bacterial infection were similar and expression of AjAIF-1 peaked at 4 hours in all tested tissues, regardless of how the pathogen entered the animal. Notably, however, AjAIF-1 expression was higher after bacterial challenge than injury, indicating that it was significantly upregulated in coelomocyctes when challenged with Vibrio splendidus. Areas such as the intestine and longitudinal muscle wall had lower expression of the gene than the coelomocytes, which could suggest that these are potentially areas of reduced inflammation response in Apostichopus japonicus. This of course has implications for the handling of the animals in aquaculture in terms of their ability to fight infection.
Hope this answers your queries :)
Hi Anita,
ReplyDeleteWas there any mention of studies on AjAIF-1 levels on wild populations at all? I assume with any intense farming method, stress and methods to fight off ailments are going to be higher.
It is interesting that that after 24 & 48 hours of infection, AjAIF-1 levels of expression were lower than the control group. Just to clarify this in my own head; when you say that the host defence response appears to be lower than pre-infection levels, are you suggesting that the mechanism in which they are fighting the stress is spent?
Thanks,
Dean
Hi Dean
ReplyDeleteThe authors didn’t mention any studies on AIF-1 levels on wild populations of sea cucumbers and it would be interesting to do a comparison between wild and farmed cucumbers. I believe there would be an increased risk of infection from damage during intense farming methods, which was what prompted the authors to investigate AjAIF-1 gene expression in farmed sea cucumbers. The reason that expression of AjAIF-1 was lower after infection than pre-infection levels wasn’t speculated in the paper. This effect was not seen after injury, where AjAIF-1 expression returned to normal after 12 hours and 4 hours seems to be an important window for immune system response against pathogens. This pattern was also seen in abalone and pearl oyster, as mentioned by De Zoysa et al., (2010) and Li et al., (2013). It appears that host defence fades after initial infection and seems to take a while to recover. Further investigation into why this might be would certainly be useful for the aquaculture industry.
I have included the references below to the papers that I mentioned in case this is of interest. Hope this helps :)
De Zoysa, M, Nikapitiya, C., Kim, Y., Oh, C., Kang, D.H., Whang, I. (2010) Allograft inflammatory factor-1 in disk abalone (Haliotis discus discus): molecular cloning transcriptional regulation against immune challenge and tissue injury, Fish Shellfish Immunology, 29, 319-326.
Li, J., Chen, J.H., Zhang, Y., Yu, Z.N. (2013) Expression of allograft inflammatory factor-1 (AIF-1) in response to bacterial challenge and tissue injury in the pearl oyster, Pinctada martensii, Fish Shellfish Immunology, 34, 365-371.