Strikingly, HIV-1 virions that display ICAM-1 in their outer membrane were found to be more infectious (2- to 9-fold) than virions without ICAM-1 [19,23], and activation of cellular LFA-1 enhanced infection with ICAM-bearing viruses by over forty-fold in both cell lines and PBMC [173,176]. This evidence concerns the gene ICAM1 and infection.