[1] KAROLINSKA INST,HUDDINGE UNIV HOSP,DEPT NEUROL,S-14186 HUDDINGE,SWEDEN
[2] KAROLINSKA INST,HUDDINGE UNIV HOSP,CLIN RES CTR,DIV MED CELL & NEUROBIOL,S-14186 HUDDINGE,SWEDEN
[3] UMEA UNIV,DEPT MED BIOCHEM & BIOPHYS,S-90187 UMEA,SWEDEN
[4] GOTHENBURG UNIV,DEPT VIROL,S-41124 GOTHENBURG,SWEDEN