S100B and infection: To further address the functional relevance of these protein products to block the endogenous RLR/IPS-1 dependent pathway, we generated CEM cell lines that were infected with retroviruses to stabely express either Vpu or Nef. We examined the ability of Vpu and Nef to inhibit IFN production and the anti-viral state induced by infection with VSV using cells stably expressing Vpu or Nef.