Expression of pro-inflammatory cytokines in rainbow trout (Oncorhynchus mykiss) during an infection with Ichthyophthirius multifiliis

Inflammatory processes are known to take place in the skin of fish during an infection with the parasitic ciliate Ichthyophthirius multifiliis. The present study shows that the pro-inflammatory cytokines interleukin 1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α), the chemokine interleukin 8 (IL-8) and the type II IL-1 receptor (IL-1RII) are expressed in rainbow trout during an infection. In the skin an up to 17.8 times increase in the expression level of IL-1β relative to uninfected controls was seen 4 days after infection. Upregulated expression of IL-1β was likewise observed in the head kidney and spleen during the infection although to a lesser degree. TNF-α expression was seen in all examined tissues, with an increase in transcript level in the skin of up to 3.2 times the level in uninfected fish. A significant increase in the expression of IL-8 was evident in the skin and also to a lower extent in the head kidney and spleen. Expression of the down regulatory IL-1RII was seen in all three tissues. The potential involvement of the expression of these genes and their relevance in an infection with I. multifiliis are discussed.