Simplexviruses successfully adapt to their host by fine-tuning immune responses

Abstract

Primate herpes simplex viruses are relatively harmless to their natural hosts, whereas cross-species transmission can result in severe disease. We performed a genome-wide scan for signals of adaptation of simplexviruses to hominins. We found evidence of positive selection in three glycoproteins, with selected sites located in antigenic determinants. Positively selected non-core proteins were involved in different immune-escape mechanisms. By expressing mutants of one of these proteins (ICP47), we show that the amino acid status at the positively selected sites is sufficient to induce HLA-G. HSV-1/HSV-2 ICP47 induced HLA-G when mutated to recapitulate residues in B virus, whereas the mutated version of B virus ICP47 failed to determine HLA-G expression. Thus, the evolution of ICP47 in HSV-1/HSV-2 determined the loss of an immunosuppressive effect, suggesting that simplexviruses tune immune responses to promote successful co-existence with their hosts. These results also help explain the high pathogenicity of B virus in humans.