Preferential depletion of gut CD4-expressing iNKT cells contributes to systemic immune activation in HIV-1 infection

Abstract

Chronic inappropriate immune activation is the central defect-driving loss of CD4(+) T helper cells and progression to AIDS in persons with HIV-1 infection, but the mechanisms remain controversial. We examined key regulatory invariant receptor natural killer T (iNKT) cells in the gut, the largest reservoir of lymphocytes and a key arena of HIV-1 pathogenesis. In healthy control persons, the anti-inflammatory CD4(+) iNKT-cell subset predominated over the pro-inflammatory CD4(-) iNKT-cell subset in the gut, but not in the blood, compartment. HIV-1 infection resulted in a preferential loss of this anti-inflammatory CD4(+) iNKT-cell subset within the gut. The degree of loss of the CD4(+) iNKT-cell subset in the gut, but not in the blood, correlated to the systemic immune activation and exhaustion that have been linked to disease progression. These results suggest a potentially important contribution of gut iNKT-cell imbalance in determining the systemic immune activation that is the hallmark of HIV-1 pathogenesis.

Figure 1

Frequencies, activation status, and functionality of bulk CD4⁺ and CD8 ⁺ T cells in the blood and gut mucosal compartments in healthy control individuals. (a–c) CD4⁺ and (d–f) CD8 ⁺ T cells are quantified and examined for expression of human leukocyte antigen (HLA)-DR and CCR5 in both the blood and gut compartments. (g–i) Cytokine production by CD4 ⁺ T cells from both the compartments after stimulation are plotted. Heavy lines represent the medians. IFN, interferon; IL, interleukin.

Figure 2

Frequencies of iNKT-cell (invariant natural killer T cell) subsets in the blood and gut mucosal compartments of healthy control individuals. (a–c) The concentrations of total, CD4⁺, and CD4⁻ iNKT cells as a percentage of all CD3⁺ T cells in blood and gut mucosal compartments are plotted. Percentages of each of these populations expressing (d–f) human leukocyte antigen (HLA)-DR and (g–i) CCR5 are plotted. Heavy lines indicate the medians.

Figure 3

Concentrations and activation of total CD4⁺ and CD8⁺ T cells in the blood and gut mucosal compartments in persons with and without HIV-1 infection. The concentrations and expression of CCR5 and human leukocyte antigen (HLA)-DR are plotted for (a–c) CD4 ⁺ and (d–f) CD8⁺ T cells in both the blood and gut mucosal compartments of persons with (gray boxes) and without (white boxes) HIV-1 infection are plotted.

Figure 4

Concentrations and activation of iNKT cells (invariant natural killer T cells) in the blood and gut mucosal compartments in persons with and without HIV-1 infection. (a) The concentrations of total iNKT cells in the blood and gut mucosal compartments are plotted, as well as (b) the ratios of the CD4⁺ to CD4⁻ iNKT cells in each of these compartments. Concentrations and expression of CCR5 and human leukocyte antigen (HLA)-DR are plotted for the (c–e) CD4⁺ and (f–h) CD4 ⁻ iNKT-cell subsets. Persons with (gray boxes) and without (white boxes) HIV-1 infection are compared.

Figure 5

Cytokine production profile of CD4⁺ T cells and iNKT-cell (invariant natural killer T cell) subsets in the blood and gut mucosal compartments in persons with and without HIV-1 infection. The concentrations of cells producing (a–c) interferon (IFN)-γ, (d–f) interleukin (IL)-4 and (g) IL-17 are indicated for total CD4⁺ T cells (a, d, g), CD4⁺ iNKT cells (b, e) and CD4 ⁻ iNKT cells (c, f) in the blood and gut mucosal compartments of persons with (gray boxes) and without (white boxes) HIV-1 infection.

Figure 6

Correlations between the balance of CD4⁺ and CD4⁻ iNKT cells (invariant natural killer T cells) to markers of immune activation and senescence in the blood and gut mucosal compartments of persons with HIV-1 infection. Plasma viremia of HIV-1-infected persons is plotted against the percentages of CD8⁺ T cells in the (a, b) gut mucosa and (d, e) blood expressing human leukocyte antigen (HLA)-DR (a, d) and programmed cell death-1 (PD-1) (b, e). Viremia is also plotted against the percentages of CD4 ⁺ iNKT cells in the (c) gut mucosa and (f) blood. The ratios of CD4 ⁺ to CD4⁻ iNKT cells in the (g–j) gut mucosal and (k–n) blood compartments are plotted against the percentages of CD8 ⁺ T cells expressing HLA-DR in the gut (g, k) and blood (i, m) or PD-1 in the gut (h, l) and blood (j, n). There were insufficient cells for PD-1 analysis of Subjects 40729, 49022, and 49023.