Co-injection of interleukin 8 with the glycoprotein gene from viral haemorrhagic septicemia virus (VHSV) modulates the cytokine response in rainbow trout (Oncorhynchus mykiss)

Since previous results showed that interleukin 8 (IL-8) was induced in rainbow trout (Oncorhynchus mykiss) in response to viral hemorrhagic septicemia virus (VHSV) infection, we have cloned IL-8 in an expression vector (pIL8+) and studied its possible adjuvant effect on the early response to a VHSV immunization model, focusing on the early response of several cytokines induced by a vector coding for the glycoprotein of VHSV (pMCV1.4-G) in the spleen and head kidney. First, we demonstrated that the pIL8+ successfully transcribed IL-8, by induction of IL-8 transcription in the muscle and blood, and by a massive infiltration of neutrophils at the muscle inoculation site. We have studied the effect of pIL8+ co-administration on the expression of two pro-inflammatory cytokines, such as IL-1β and tumour necrosis factor α (TNF-α); cytokines that have mainly an inhibitory role, IL-11 and transforming growth factor β (TGF-β); and a Th1 type cytokine, IL-18. We demonstrated that the co-administration of pIL8+ with pMCV1.4-G modulates the cytokine response that is induced, mainly by having its effect increasing pro-inflammatory cytokines (IL-1β and TNF-α1), with a greater impact on the spleen, and to a lesser extent in the head kidney. All these data suggest that IL-8 is able to modulate the early cytokine immune response that is produced in response to a DNA vaccine, and therefore, might be a potential immune adjuvant in fish viral vaccination. More work should be done to determine if this modulation has a beneficial effect on protection as seen in other mammal viral models.