2 and subjected to real-time PCR to determine the amounts of 244 DI RNA, genomic segment 1 RNA, and segment 7 RNA (Fig. 3). The levels of segments 1 and 7 RNA on day 2 after infection were similar in the lungs of mice given either inactivated DI virus + A/WSN or active DI virus + A/WSN. On day 4 there was 5-fold less segment 7 and 12-fold less segment 1 in the active DI virus + A/WSN than MG 132 in the control group but by day 6 both groups had similar amounts of segments 1 and 7. At this point the levels of segments 1 and 7 in the lungs of the inactivated DI virus + A/WSN group reached a plateau, while those in the active DI virus + A/WSN group reached a plateau

from day 8. On day 8 mice in the inactivated DI + A/WSN group were very sick indeed, and the amount of RNA in replicate lungs varied by over 100-fold making the mean unreliable. The majority of mice in this group died shortly thereafter. In both groups, levels of segment 7 RNA were consistently

5 to 10-fold greater than those of segment 1. The reasons for this are unclear but as the PCR primers are vRNA specific this appears to be a genuine difference. This is consistent with studies with studies of synchronized infection of cells in vitro in which segment 7 RNA was 9-fold greater than the combined RNAs1 to 3 [36] or 2-fold greater than RNA 1 early in infection [37]. There was an initial high level of approximately 108 copies of 244 DI RNA in the lungs of SCID mice inoculated with the active DI virus + A/WSN, through and about 100-fold lower in the group Vismodegib in vitro that received inactivated DI virus + A/WSN. The latter represents UV-fragmented 244 RNA and residual intact 244 RNA (Fig. 3c and d). After 2 days there was undetectable 244 DI RNA in the lungs of mice inoculated with inactivated DI virus + A/WSN (Fig. 3c and d), whereas the amount in the active

DI virus + A/WSN group was unchanged. 244 RNA in the active DI virus-protected group then maintained a modest but steady rise to nearly 109 copies per lung by day 8, and remained between 108 and 109 copies until day 16 when most of the mice were dead. The RNA was clearly being replicated as mice that received only active DI virus showed a steady decline in amounts of 244 RNA (Fig. 3d open squares). Thus substantial amounts of 244 RNA were present in mice inoculated with DI + A/WSN throughout both the initial period of good health (up to and including day 9) and through the period of delayed onset disease (days 10–16). In contrast 244 DI RNA in the lungs of mice inoculated with inactivated DI virus + A/WSN increased from day 2 to day 4 reflecting rapid replication of residual amounts of DI RNA that remained after the UV-irradiation (Fig. 3c). The 244 RNA increased to a maximum on day 6, but this was evidently too late to be of benefit as 75% of mice already showed signs of clinical disease on day 4.