Immunoevasive strategies: Host and virus

Abstract

Despite their heterogeneity, viruses from different families, including RNA and DNA viruses, have evolved similar gene functions that target many common cellular targets for immunoevasion. In most cases the goal is not a complete escape from recognition of the immune system, since this would destroy the host and limit virus replication and spread, but rather a balance between clearance and persistence that allows coexistence of the virus and its immunocompetent host. Nevertheless, there are fundamental differences between large DNA viruses (e.g. herpesviruses, poxviruses and adenoviruses) and small RNA viruses (e.g. retroviruses, picornaviruses and myxoviruses) where immunoevasion is concerned. The latter have genomes of limited size, a trait possibly linked to the low fidelity of the viral RNA polymerase. These RNA viruses therefore mainly carry multifunctional genes that are essential for virus replication and their genome does not have a lot of exon space for accessory immunomodulatory genes. Rather, they rely on a high mutation rate to alter the antigenicity of the virus, thus escaping B- and T-cell recognition and antiviral antibodies (see example of Influenza virus type A below). Another general strategy of the fastreplicating small RNA viruses is to overwhelm the host with an enormous number of infectious particles (high virus load) following the motto "mass versus cleverness".