Istituto di Cardiologia, Universita' Cattolica del S. Cuore, Rome, Italy (G.L., L.M.B., A.G.R. G.C., G.A.L., G.Q., C.M., A.M.), and Immunological Medicine Unit, Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London, UK (J.R.G., M.B.P.). (At 1996-11-15)