Figure 1

A set of imperfect multiple barriers provides gatekeeps against HIV-1 better than a single "perfect" barrier (adapted from [194]). (a) A "perfect" barrier protects against X4 HIV-1 (left panel). If this barrier is breached (right panel), there is no protection against X4 HIV-1 infection. (b) A series of ‘imperfect’ barriers (left panel), each of which protects against X4 virus infection only five times more efficiently than against R5 HIV-1. Nevertheless the chance for X4 HIV-1 to penetrate these barriers is 3125 times lower than for R5. If one of the barriers is breached, (right panel) the system retains relatively high selectivity: The chance for X4 HIV-1 to penetrate the barriers is still 625 times lower than for R5 HIV-1.