First, the lack of strong induction of CD4+ T-cell proliferation by IL-7, unlike IL-15, which was detectable only transiently and only after the first IL-7 injection; of note, this transient proliferative effect of IL-7 could have been responsible for the significant increase in SIV plasma viremia at the earliest time point tested (day 4 post-infection). This evidence concerns the gene IL7 and infection.