V and C proteins of measles virus function as virulence factors in vivo

The measles virus (MV) P gene encodes three proteins: the P protein and two nonstructural proteins, C and V. Because the functions of both the C and V protein are unknown, we used MV C (C-) and V (V-) deletion recombinants ge nerated by the MV reverse genetics system (F. Radecke, P. Spielhofer, H. Sc hnieder, K. Kaelin, M. Huber, C. Dotsch, G. Christiansen, and M. A. Billete r 1995. EMBO J. 14, 5773-5784). Compared to parental Vaccine strain, Edmons ton (Ed) MV, both had normal growth and cytopathic effects in Vero cells an d showed similar growth kinetics in human neuroblastoma SK-N-MC cells and i n primary mouse neurons expressing the MV receptor, CD46. However, in vivo, using YAC-CD46 transgenic mice as a model for MV induced CNS disease (M. B . A. Oldstone, H. Lewicki, D. Thomas, A. Tishon, S. Dales, J. Patterson, M. Manchester, D. Homann; D. Naniche, and A. Holt 1999; Cell 98, 629-640), C- and V- viruses differed markedly from wt Ed(V+C+) virus. Newborn mice inoc ulated-with as little as 10(3) PFU of Ed strain became ill and died after 1 0-15 days. In contrast, those inoculated with 10(3) or 10(4) PFU of MV C- o r MV V- showed significantly fewer and milder clinical symptoms and had a l ower mortality. A total of 10(5) PFU V- Virus were required to kill most YA C-CD46 mice, and less than half (44%) were killed with a corresponding dose of MV C-. Immunohistochemical staining for MV antigens showed similar exte nts of spread for MV C- and MV Ed but restricted spread for MV V- throughou t the brain. Viral load and transcription were markedly reduced for V-but n ot for C-. Multiple cytokines and chemokines were equivalently upregulated for all three viruses. Therefore, MV C and V proteins encode virulence func tions in vivo and likely operate via separate mechanisms. (C) 2000 Academic Press.