BM-based CD4⁺ T-cell proliferation contributes to preserve a normal CD4⁺ T-cell compartment in SMs after SIV infection. Levels of CD4⁺ T-cell proliferation in SIV-infected SMs that preserve, or not, the peripheral homeostasis of the CD4⁺ T-cell compartment. (A, left) Although the majority of SIV-infected SMs maintain a CD4⁺ T-cell count more than 500/mm³ (CD4 normal), a small percentage of these animals (∼10%) show a CD4⁺ T-cell count less than 500/mm³ (CD4 low, gray box). Two SMs were not included in the analysis because their levels of CD4⁺ T cells were too low to accurately determine the expression of Ki-67. (A, right) Percentage of CD4⁺Ki-67⁺ T cells in BM, PB, and LN of 10 SIV-infected SMs defined as “CD4 normal” (▲) and 10 SIV-infected SMs defined as “CD4 low” (). P values are shown when significant differences between groups are present. (B) In SIV-infected SMs, peripheral CD4⁺ T-cell count correlates directly with the percentage of proliferating CD4⁺ T cells in BM (left panel) and inversely with the percentage of proliferating CD4⁺ T cells in PB (right panel). P values of the correlation coefficient (Spearman rank correlation test) are shown.