IFNB1 and cytomegalovirus infection: Moreover, the results indicated that in U251–UL23 cells, both HCMV ΔUL23 and HCMV Towne were insensitive to IFN-β treatment and exhibited high viral titters with IFN-β (Figure 1B), suggesting that ectopic UL23 expression represses IFN-β action upon HCMV infection.