I injected 4X10E12 AAV-IL4 in mice via iv injection, 5 Days later, mice die. The control mice were fine up to 5X10E13. Is that because of side effection of IL4 overexpression?
There is a paper shows "Overexpression of interleukin-4 delays virus clearance in mice infected with respiratory syncytial virus." This may be the reason why your mice died. You may check this paper.
May be some liver inflammation (in line with the connection of IL4 with conA-induced hepatitis). I dont know whether the IV route is making it more damaging compared to other studies showing positive effects..
I can't imagine that the AAV even with large quantities of IL-4 would be inducing disease. I think the following paper, which suggests liver pathology is more likely to explain your problem.
"Lethal Hepatitis After Gene Transfer of IL-4 in the Liver Is Independent of Immune Responses and Dependent on Apoptosis of Hepatocytes: A Rodent Model of IL-4-Induced Hepatitis" by Guillot et al. in J. Immunol. 2001 Apr 15;166(8):5225-35.