MXA GENE-EXPRESSION AFTER LIVE VIRUS VACCINATION - A SENSITIVE MARKERFOR ENDOGENOUS TYPE-I INTERFERON

MxA gene expression is known to be regulated tightly and exclusively b y type I interferons (IFNs). The kinetics of MxA gene expression was a nalyzed in peripheral blood mononuclear cells from 11 healthy voluntee rs vaccinated with the 17-D strain of yellow fever virus. A reliable i nduction of MxA RNA and MxA protein was found in the absence of easily detectable serum IFN activity. Thus, steady-state Mx4 RNA levels were elevated 8- to 30-fold above prevaccination levels on day 5 after vac cination. The average increase of MxA protein was similar to 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 va ccinations. The IFN marker 2'-5'-oligoadenylate (2-5A) synthetase know n to react to both type I and type II IFNs showed a similar response b ut did not differentiate equally well between nonimmune and immune vac cinees. beta(2)-micraglobulin and neopterin reacted poorly, remaining at low levels within the normal range. These results demonstrate that MxA gene expression is a good marker for detecting minute quantities o f biologically active type I IFN during viral infections.