Circulating (1→3)-β-D-glucan Is Associated With Immune Activation During Human Immunodeficiency Virus Infection

Abstract

Background: Microbial translocation from the gut to systemic circulation contributes to immune activation during human immunodeficiency virus (HIV) infection and is usually assessed by measuring plasma levels of bacterial lipopolysaccharide (LPS). Fungal colonization in the gut increases during HIV-infection and people living with HIV (PLWH) have increased plasma levels of fungal polysaccharide (1→3)-β-D-Glucan (βDG). We assessed the contribution of circulating DG to systemic immune activation in PLWH.

Methods: Cross-sectional and longitudinal assessments of plasma βDG levels were conducted along with markers of HIV disease progression, epithelial gut damage, bacterial translocation, proinflammatory cytokines, and βDG-specific receptor expression on monocytes and natural killer (NK) cells.

Results: Plasma βDG levels were elevated during early and chronic HIV infection and persisted despite long-term antiretroviral therapy (ART). βDG increased over 24 months without ART but remained unchanged after 24 months of treatment. βDG correlated negatively with CD4 T-cell count and positively with time to ART initiation, viral load, intestinal fatty acid-binding protein, LPS, and soluble LPS receptor soluble CD14 (sCD14). Elevated βDG correlated positively with indoleamine-2,3-dioxygenase-1 enzyme activity, regulatory T-cell frequency, activated CD38+Human Leukocyte Antigen - DR isotype (HLA-DR)+ CD4 and CD8 T cells and negatively with Dectin-1 and NKp30 expression on monocytes and NK cells, respectively.

Conclusions: PLWH have elevated plasma βDG in correlation with markers of disease progression, gut damage, bacterial translocation, and inflammation. Early ART initiation prevents further βDG increase. This fungal antigen contributes to immune activation and represents a potential therapeutic target to prevent non-acquired immunodeficiency syndrome events.

Keywords: (1→3)-β-D-glucan; HIV; antiretroviral therapy; immune activation; microbial translocation.

Figure 1.

Study design and classification of study participants. The study population included 146 PLWH and 42 UCs. PLWH were then further classified into various subgroups depending on the duration of infection and whether they had initiated treatment. Abbreviations: ART−, antiretroviral therapy naive; ART+, on antiretroviral therapy; CHI, chronic HIV infection; EHI, early HIV infection; HIV, human immunodeficiency virus; PLWH, people living with HIV; UC, uninfected control.

Figure 2.

Cross-sectional and longitudinal plasma levels of βDG during different stages of HIV infection. A, βDG concentrations increased from EHI to CHI and remained unchanged with ART (EHI ART−, n = 42; EHI ART+, n = 11; CHI ART−, n = 22; CHI ART+, n = 71; UCs, n = 42). B, Longitudinal analysis showed an increase in βDG levels over 24 months in the absence of ART (n = 14). C, Longitudinal analysis showed that 24 months of ART, initiated during EHI, prevented an increase in βDG plasma levels (n = 21). P values show Kruskal-Wallis tests with Dunn’s post hoc test between different groups. Abbreviations: ART, antiretroviral therapy; ART−, antiretroviral therapy naive; ART+, on antiretroviral therapy; CHI, chronic HIV infection; EHI, early HIV infection; HIV, human immunodeficiency virus; UC, uninfected controls; βDG, (1→3)-β-D-glucan. *P < .05; **P < .01; ***P < .001; ****P < .0001.

Figure 3.

Comparison of βDG with markers of bacterial translocation, gut damage, and HIV disease progression. A, βDG levels correlated with plasma LPS in EHI and CHI participants (ART+ and ART−) (n = 146). B, βDG concentrations correlated with plasma sCD14 in EHI participants (ART+ and ART−) (n = 67). C, βDG concentrations in plasma were associated with plasma I-FABP in CHI participants (n = 93). D, βDG concentrations were correlated with plasma viral load in untreated participants (n = 78). E, βDG concentrations were correlated with CD4 T-cell count in EHI and CHI participants (ART+ and ART−) (n = 146). F, βDG concentrations were correlated with CD4-to-CD8 ratio in EHI and CHI participants (ART+ and ART−) (n = 146). P values show nonparametric Spearman correlations. EHI ART− = blue; EHI ART+ = red; CHI ART− = green; CHI ART+ = purple. Abbreviations: ART, antiretroviral therapy; ART−, antiretroviral therapy naive; ART+, on antiretroviral therapy; CHI, chronic HIV infection; EHI, early HIV infection; HIV, human immunodeficiency virus; I-FABP, intestinal fatty acid–binding protein; LPS, lipopolysaccharide; sCD14, soluble LPS receptor; VL, viral load; βDG, (1→3)-β-D-glucan.

Figure 4.

βDG correlated with markers of immune activation ex vivo. βDG levels correlated with plasma IL-6 (n = 146) (A) and IL-8 (n = 146) (B) in PLWH. βDG levels correlated with frequency of CD4+CD38+HLA-DR+ T cells (n = 26) (C) and CD8+CD38+HLA-DR+ T cells (n = 26) (D) in PLWH. E, βDG levels correlated with kynurenine (Kyn)-to-tryptophan (Trp) ratio (n = 67). F, βDG levels correlated with frequency of CD25^highCD127^lowFoxP3^high Tregs (n = 67). P values show nonparametric Spearman correlations. EHI ART− = blue; EHI ART+ = red; CHI ART− = green; CHI ART+ = purple. Abbreviations: ART−, antiretroviral therapy naive; ART+, on antiretroviral therapy; CHI, chronic HIV infection; EHI, early HIV infection; HIV, human immunodeficiency virus; IL, interleukin; PLWH, people living with HIV; Treg, regulatory T cell; βDG, (1→3)-β-D-glucan.

Figure 5.

Analysis of βDG receptors on monocytes and NK cells ex vivo. A, Dectin-1 MFI on monocytes of participants in different stages of HIV infection (EHI ART−, n = 7; EHI ART+, n = 7; CHI ART−, n = 6; CHI ART+, n = 6; UCs, n = 7). B, βDG levels were inversely correlated with Dectin-1 MFI on monocytes during HIV infection (n = 26). C, NKp30 MFI on CD56^dim NK cells of participants in different stages of HIV infection (EHI ART−, n = 7; EHI ART+, n = 7; CHI ART−, n = 6; CHI ART+, n = 6; UCs, n = 7). D, βDG levels inversely correlated with NKp30 MFI on CD56^dim NK cells in HIV-infected participants (n = 26). P values show nonparametric Kruskal-Wallis test between different groups. EHI ART− = blue; EHI ART+ = red; CHI ART− = green; CHI ART+ = purple; UC = Brown. *P < 0.05, **P < 0.01. Abbreviations: ART−, antiretroviral therapy naive; ART+, on antiretroviral therapy; CHI, chronic HIV infection; EHI, early HIV infection; HIV, human immunodeficiency virus; MFI, mean fluorescence intensity; NK, natural killer; UC, uninfected controls; βDG, (1→3)-β-D-glucan.