MxA Gene Expression after Live Virus Vaccination: A Sensitive Marker for Endogenous Type I Interferon

MxA gene expression is known to be regulated tightly and exclusively by type I interferons (IFNs). The kinetics of MxA gene expression was analyzed in peripheral blood mononuclear cells from 11 healthy volunteers vaccinated with the 17-D strain of yellow fever virus. A reliable induction of MxA RNA and MxA protein was found in the absence of easily detectable serum IFN activity. Thus, steady-state MxA RNA levels were elevated 8- to 30-fold above prevaccination levels on day 5 after vaccination. The average increase of MxA protein was ∼50-fold. In contrast, no induction of MxA RNA or MxA protein was detectable in 3 similarly vaccinated controls who were immune because of previous vaccinations