The Distribution and Immune Profile of T Cell Subsets in HIV-Infected Children from Uganda

Abstract

Abstract T cell activation is an important mechanism in HIV-associated immune depletion. We have previously demonstrated an association between the hyperactivation of CD4(+) and CD8(+) T cells and low CD4 status in HIV-infected Ugandan children. In this study, we explore differences in activation between naive and memory T cells in HIV-infected Ugandan children. A significant correlation between CD4- and CD8-mediated immune activation and CD4 status was observed only in the memory T cells. Antiretroviral (ART) untreated and treated HIV-positive and HIV-negative children displayed similar profiles of activation and distribution within the CD4(+) naive T cells. In contrast, significantly higher immune activation of the memory CD4(+) T cell subset was seen in ART-untreated children when compared to ART-treated or HIV-negative children. ART-mediated viral suppression led to the correction of CD4(+) immune activation to levels seen in uninfected children but did not increase the size of the memory CD4(+) T cell population. High levels of CD8(+) immune activation were also found in both naive and memory cell subsets. Antiretroviral treatment led to the normalization of CD8(+) T cell activation but did not correct the distribution of naive CD8(+) T cells. We also assessed PD-1 expression on CD8(+) T cells as a measure of immune dysfunction. Upregulation of PD-1 was highest in untreated children but persisted in ART-treated children compared to uninfected children. The mechanisms of immunopathogenesis in pediatric HIV infection likely involve distinct contributions from individual naive and memory T cells subsets.

FIG. 1.

(A) Distribution of CD4⁺ T cell subsets as defined by total naive (striped pattern) or memory (clear pattern) cells in a group of antiretroviral-naive children (N = 40), ART experienced with undetectable viral load (N = 20), or healthy HIV-negative children (N = 25). Horizontal lines represent medians and interquartile ranges (25th and 75th percentiles). (B) Immune activation in CD4⁺ T cell memory subsets was defined as the percentage of CD4⁺ T cells with the CD45RA⁻CD27^+/− phenotypes with surface coexpression HLA-DR and CD38. Immune activation was significantly higher in untreated children compared to ART-suppressed or HIV-negative children (p < 0.001).

FIG. 2.

Correlation between the CD4% and memory T cell activation in children. The percentage of (A) CD4⁺ memory T cell activation or (B) CD8⁺ memory T cell activation is plotted against CD4%. A significant negative was observed in (A) (r = −0.43, p = 0.007) and in (B) (r = −0.034, p = 0.04).

FIG. 3.

(A) Distribution of CD8⁺ T cell subsets as defined by total naive (striped pattern) or memory (clear pattern) cells in a group of antiretroviral-naive children (N = 40), ART experienced with undetectable viral load (N = 20), or healthy HIV-negative children (N = 25). Horizontal lines represent medians and interquartile ranges (25th and 75th percentiles). Immune activation in CD8 T cell subsets was defined as the percentage of total naive (B) or memory (C) CD8⁺ T cells expressing HLA-DR and CD38. Significant differences were observed in immune activation of the memory CD8⁺ T cell subpopulation between HIV-positive and HIV-negative children (p < 0.001).

FIG. 4.

PD-1 expression on CD8⁺ T cells is higher in HIV-positive children. Dead cells were first gated out using a violet excited viability dye (LIVE/DEAD Fixable Dead Cell Stain; Invitrogen). Samples were subsequently gated on the CD3⁺/CD8⁺ lymphocyte population then the percent of PD-1-positive cells was determined. Gating was standardized and set using the fluorescence minus one (FMO) control for PD-1. (A) PD-1 expression on CD8⁺ T cells was highest in children not receiving ART (p < 0.0001). Viral suppression does not lead to normalization of PD-1 expression compared to samples from HIV-negative children (p = 0.004). (B) The presence of PD-1 expression negatively correlated with the frequency of naive CD8⁺ T cells (r = −0.53, p = 0.003) and (C) positively associated with naive CD8⁺ T cell activation (r = 0.42, p = 0.01).

FIG. 5.

(A) Distribution of CD4⁺ and CD8⁺ T cell subsets as defined by total naive or memory cells with horizontal lines representing medians and interquartile ranges (25th and 75th percentiles) in a group of untreated HIV-positive Ugandan adults (N = 27). The median distributions of memory phenotypes on CD4⁺ and CD8⁺ T cells were 76% and 55%, respectively. (B) Immune activation in CD4⁺ and CD8⁺ T cell subsets. Naive and memory T cell activation was defined as the percentage of CD45RA⁺CD27⁺ or CD45RA⁻CD27^+/− cells expressing HLA-DR and CD38, respectively. Median naive and memory CD4⁺ T cell activation was 22% and 2%, respectively. Median naive and memory CD8⁺ T cell activation was 53% and 21%, respectively.