Question

Restriction factors acts as the first line of host defense against retroviral infection

Answer 1

Some restriction factors appear to specifically inhibit retrovirus replication, ... and we have come to appreciate that variation in host defenses is a critical determinant of host range.

Answer 2

Key retroviral restriction factors are shown in red, ... First, they are encoded by functionally autonomous, .... clearly evolved to act in particular primate host species.