(A) Frequencies of SIV RNA+ cells in lymph nodes. (B) Frequencies of SIV RNA+ cells in B cell follicles (F) compared to extrafollicular regions (EF) of lymph nodes. (C) Percentage of tissue that consisted of follicle did not differ among animals by disease stage. (D) Percentages of SIV RNA+ cells within B cell follicles. (E) Frequencies of SIV RNA+ cells within lymph nodes predicted plasma viral load. For every 1 log10 increase in SIV RNA+ cells, there was a 1.40 log10 (95% CI, 0.35, 2.45) increase in plasma viral load. (F) The F:EF ratio of SIV RNA+ cells in lymph nodes predicted plasma viral load. On average, viral load decreased by 4.0 log10 (95% CI, −5.33, −2.67) copies/mL for each 1 log10 increase in F:EF. This relationship did not significantly differ by disease stage (p=0.30). Furthermore, when the analysis was restricted to animals with chronic, asymptomatic infection, results were still statistically significant (p=0.0078), with viral load decreases by 3.04 log10 (95%CI −5.12, −0.96) copies/mL for each 1 log10 increase in F:EF. Dotted lines link data points from animals that were sampled in more than one disease stage. Horizontal lines indicate geometric mean (GM) values.