When good turns bad: how viruses exploit innate immunity factors

• Viruses hijack selected restriction factors for efficient replication. • Factors promoting viral entry may in turn impair virion release and infectivity. • Endogenous and overexpressed factors may have opposing effects on virus infection. • RNA editing factors inhibit viral pathogens but also accelerate viral evolution. Humans evolved numerous cell-intrinsic restriction factors as a first line of defense against viral pathogens. Typically, they inhibit efficient viral replication and thus prevent viral zoonoses and pandemics. However, viruses show enormous adaptability and are well known for their ability to counteract antiviral mechanisms. Accumulating evidence shows that some viruses are even capable of exploiting antiviral factors for efficient infection. In addition, antiviral factors may exert enhancing effects under specific circumstances. While much progress has been made in understanding the antiviral mechanisms of restriction factors, their proviral effects are poorly defined. Here, we summarize current knowledge on how viral pathogens may exploit otherwise antiviral cellular factors for efficient infection and replication.