Infection of LuSIV cells with the wild-type and DS1C/A mutant virus followed by IFNβ treatment at 4 h postinfection demonstrated that IFNβ downregulates LTR activity of both wild-type and DS1C/A genotype by 50% at 48 h postinfection (similar reduction was seen at 24 h postinfection with IFNβ treatment, data not shown). The gene discussed is IFNB1; the disease is infection.