Meanwhile, using recombinant VACV expressing mouse IL-10 (mIL-10) it has been shown that in immunocompetent mice mIL-10 expressed from the VACV genome affected natural killer (NK) and virus-specific CTL activity, whereas in severe combined immunodeficient (SCID) mice VACV-mIL-10 infection resulted in increased NK cell activity and higher degree of virus clearance compared to infection with control VACV (Kurilla et al., 1993). This evidence concerns the gene IL10 and infection.