Table 1.

Virulence of hvPR8 viruses with NS1 deletions in mice

LD₅₀ values (shown as f.f.u.) were determined by infecting groups (n=4) of wild-type and mutant mice (C57BL/6 genetic background) with various doses (10¹–10⁶ f.f.u.) of the indicated viruses as described by Reed & Muench (1938). Animals were killed if severely ill or if weight loss approached 30 %. nd, Not done.

Virus strain	Mouse strains
	Mx1−/−	Mx1+/+	Mx1+/+IFNAR10/0	Mx1+/+IFNAR10/0IL28R0/0
hvPR8-wt	<10	50	nd	nd
hvPR8(1–126)	<10	5×104	3×103	50
hvPR8-delNS1	105	>2×105	>2×105	103