S100B and infection: For tetherin counteraction, maintenance of function reflects other reports of immunodeficiency viruses responding to the pressure exerted by tetherin, including the recent characterisation of a HIV-1 group N Vpu that has evolved to become an efficient tetherin antagonist [13], the demonstration of acquisition of tetherin antagonism in the Env proteins of nef-deleted simian immunodeficiency viruses [45], and the reacquisition of tetherin counteractivity in Nef following experimental infection of chimpanzees with HIV-1 [46].