SIV viral load is dependent on Th17 cell development before infection. (A) Longitudinal plasma viral load levels, after color-coding the plotted points according to the baseline frequency of Th17 cells coexpressing IFN-γ (red for highest frequency of Th17 levels at baseline). (B) Correlation between the frequency of baseline IFN-γ+ Th17 cells and plasma viremia at week 2 postinfection. (C) Correlation between the frequency of IFN-γ+ Th17 cells and the frequency of CD8+ T cells expressing both CCR4 and CCR6 at baseline. (D) Baseline immune cell populations associated with dam versus nursery rearing plotted along the first two principal components after color-coding the plotted points according to the eventual average viral load (red for highest viral load). (E) Correlation between baseline first principal component axis (“development index”) and viral loads at weeks 2, 4, 8, 12, and 16 postinfection (each colored line represents a best fit for one postinfection time point, e.g., the purple fitted line represents the association between viral loads at 16 weeks postinfection development indices for each animal). (F) Correlation between baseline first principal component axis (“development index”) and viral loads at week 16. Th17, T helper 17.