[1] Univ Cologne, Inst Genet, D-50931 Cologne, Germany
[2] Univ Cologne, Inst Anat 1, D-50931 Cologne, Germany
[3] Univ Zurich, Inst Expt Immunol, CH-8093 Zurich, Switzerland
[4] Osaka Univ, Sch Med, Dept Mol Immunol, Microbial Dis Res Inst, Suita, Osaka 565, Japan
[5] Osaka Univ, Sch Med, Dept Med 3, Suita, Osaka 565, Japan
[6] Tokyo Med & Dent Univ, Med Res Inst, Dept Mol Cell Biol, Tokyo 101, Japan