TNF and infection: The results indicate a stimulatory effect of infection on IGF-I and TNF-α gene expression in the spleen: IGF-I was elevated 6.802-fold (p = 0.0001) at Day 3 after infection with 106 colony-forming unit (CFU) of Yersinia ruckeri [86,87] and TNF-α gene expression 60.497-fold (p = 0.001) as compared with the uninfected control [44].