Figure summarizes the differences between pathogenic HIV/SIV infections SIV and natural host monkey species; specifically with regard to the acute-to-chronic transition phase following an SIV or HIV infection. Within the graphs the blue line represents typical viral load levels, the green line and shaded green area represent typical CD4 levels, the red line represents general systemic immune activation which can be measured in a number of ways including the activation state of the immune cells and levels of interferon stimulated genes (ISGs). Vertical dotted lines indicate the time of acute-to-chronic transition which generally occurs between approximately 21 and 40 days. Some specific differences in the acute-to-chronic phase between pathogenic and natural host infections are listed within the dashed boxes below the graphs.