IL10 and infection: In the challenge with CEV genogroup I (Co II), koi depicted significant lower level of IL-10 and higher levels of IL-6a on day 6th post-infection compared to day 0 p.i. On 11th dpi, koi showed significantly higher level of IL-1β, TNF-α2 and IL-6a genes, and significant down-regulation of IL-10 gene expression compared to day 0 (Fig. 1).