Regulation of rainbow trout (Oncorhynchus mykiss) interleukin-8 receptor (IL-8R) gene transcription in response to viral hemorrhagic septicemia virus (VHSV), DNA vaccination and chemokines

An interleukin-8 receptor (IL-8R)-like sequence has been previously reported in rainbow trout (Oncorhynchus mykiss); however, no further studies to confirm its biological activity or regulation of expression have been performed. In this report, we have studied the regulation of the transcription of this receptor in response to different stimuli both in vivo and in vitro. We found that in response to a viral hemorrhagic septicemia virus (VHSV) infection, the levels of expression of IL-8R are suppressed in the head kidney, spleen and muscle, in contrast to what occurs in response to Poly I:C. These results might indicate a suppressive effect of the virus and a mechanism that enables it to elude the immune response. This response is no longer observed in vitro in the rainbow trout macrophage cell line RTS11, which has been shown to be resistant to VHSV complete replication, and where the virus produced no effect on the levels of mRNA expression of IL-8R. In these cells, as observed in vivo, Poly I:C significantly induced the expression of IL-8R, increase that came along with an increase in the chemotactic activity towards IL-8. In response to DNA vaccination, we found that the levels of mRNA expression are significantly increased only in the muscle at very early times post-vaccination. As an additional step to clarify whether this receptor is in fact being used by IL-8, we intramuscularly injected plasmids coding for different rainbow trout chemokines (IL-8 and other CC chemokines such as CK5B, CK6 and CK7A). Only plasmids coding for IL-8 and CK-6 were capable of significantly increasing the levels of transcription of IL-8R in the muscle. This effect was confirmed by the up-regulation of IL-8R mRNA production in head kidney leucocytes in response to recombinant IL-8 and CK-6.