<unk>  refers to a set of cellular-based anti-viral defense mechanisms, notably genetically encoded proteins which specifically target eukaryotic retroviruses. Unlike adaptive and innate immunity effectors,<unk>  immune proteins are usually expressed at a constant level, allowing a viral infection to be halted quickly.<unk>  antiviral immunity refers to a form of innate immunity that directly restricts viral replication and assembly, thereby rendering a cell non-permissive to a specific class or species of viruses.<unk>  is conferred by restriction factors preexisting in certain cell types, although these factors can be further induced by virus infection.<unk>  viral restriction factors recognize specific viral components, but unlike other pattern recognition receptors that inhibit viral infection indirectly by inducing interferons and other antiviral molecules,<unk>  antiviral factors block viral replication immediately and directly.
Intrinsic immunity
Humoral immunity
Social immunity
Immune response
Histocompatibility
Contact immunity
Intravascular immunity
Immune tolerance