Tuberculosis distorts the inhibitory impact of interleukin-10 in HIV infection

Abstract

Objectives: This study aimed to assess how Mycobacterium tuberculosis (MTB) coinfection alters the impact of interleukin-10 in chronic HIV infection.

Design: We assessed plasma cytokine levels (interleukin-10, interferon-γ, tumor necrosis factor-α, interleukin-2, interleukin-6 and interleukin-13) in 82 individuals presenting with HIV monoinfection, HIV-LTBI (latent MTB infection) coinfection or HIV-TB (active tuberculosis) coinfection. We also assessed the influence of MTB on the functional impact of interleukin-10 receptor alpha (interleukin-10Rα) blockade on HIV and MTB-specific CD4(+) T cells.

Methods: Plasma cytokine levels were measured by high sensitivity Luminex. We used an ex-vivo interleukin-10Rα blockade assay to assess if functional enhancement of HIV and MTB-specific CD4(+) T cells was possible following a 48-h stimulation with HIV gag or pooled ESAT-6 (6 kDa early secretory antigenic target) and CFP-10 (10-kDa culture filtrate protein) peptides. Cell supernatant was collected 48 h after stimulation and the cytokine profile was measured by Luminex.

Results: Plasma interleukin-10 levels were elevated in HIV-TB as compared with HIV monoinfection (P < 0.05) and HIV-LTBI (P < 0.05). Plasma interleukin-10 levels correlated to HIV viral load in HIV monoinfection (P = 0.016) and HIV-LTBI (P = 0.042), but not HIV-TB. Ex-vivo blockade of interleukin-10Rα significantly enhanced MTB and HIV-specific CD4(+) T-cell function in HIV-LTBI individuals but not in HIV-TB individuals.

Conclusion: Tuberculosis disrupts the correlation between interleukin-10 and markers of HIV disease progression. In addition, HIV-TB is associated with a more inflammatory cytokine milieu compared with HIV monoinfection. Interestingly, interleukin-10Rα blockade can enhance both HIV and MTB-specific T-cell function in HIV-LTBI, but not in HIV-TB coinfection.

Fig. 1. Interleukin-10 levels are distorted in HIV coinfection with tuberculosis

IL-10 plasma levels significantly differed across all patient groups (P=0.0130) (a). Multiple comparison analysis revealed that IL-10 plasma levels were significantly higher in HIV-positive individuals co-infected with tuberculosis (TB) (HIV+/TB) individuals as compared with HIV mono-infected individuals (P<0.05) and HIV-positive individuals co-infected with latent M. tuberculosis infection (HIV-LTBI)(P<0.05). The ratio of IFN-γ/IL-10 was assessed (b). There was a significant difference in the IFN-γ/IL-10 ratios across patient groups (P=0.0382). Specifically, a greater IFN-γ/IL-10 ratio was observed in HIV-TB as compared with HIV mono-infection (P<0.05). The ratio of IL-10 was also correlated to markers of HIV disease progression. We created a cytokine secretion profile by calculating the percentage contribution of each measured cytokine to the overall pool. Both the cytokine profiles from HIV-LTBI (P<0.05) and HIV-TB (P<0.01) differed significantly from HIV mono-infection(c). In HIV mono-infection, IL-10 dominated the cytokine secretion profile. HIV-LTBI coinfection was associated with a lower contribution of IL-10 (38%) and a higher contribution of IL-13 (19%) and IFN-γ (12%). HIV-TB coinfection was characterized by a strikingly high contribution of IFN-γ (27%), almost equal to that of IL-10 (31%). A strong inverse correlation between CD4⁺ T-cell count and IL-10 plasma levels was observed in HIV-LTBI (P=0.0002, r=−0.68) with a correlation between log viral load and IL-10 (P=0.01, r=0.46) (d). These correlations were not present in HIV-TB (e). Conversely, TNF-α did not correlate to HIV viral load in HIV-LTBI (P=0.27) (d) but did correlate to HIV viral load in the HIV-TB group (P<0.001) (e). IFN, interferon; IL, interleukin; TNF, tumor necrosis factor.

Fig. 2. Interleukin-10 receptor alpha blockade enhances HIV and M. tuberculosis-specific CD4⁺ T-cell function in HIV coinfection with latent M. tuberculosis but not tuberculosis

(a) Blockade of IL-10Rα in HIV coinfection with latent M. tuberculosis infection (LTBI), enhanced HIV-specific CD4⁺ T-cell secretion of (i) IFN-γ (P=0.01) and (ii) TNF-α (P=0.02) but not IL-2 (iii) (P=0.93). In contrast, blockade of the IL-10 pathway in HIV-TB coinfection did not restore HIV-specific CD4⁺ T-cell function (b). Enhancement of MTB-specific function was also assessed. (c) Blockade of IL-10Rα in HIV-LTBI coinfection enhanced MTB-specific CD4⁺ T-cell secretion of (i) IFN-γ (P=0.007), (ii) TNF-α (P=0.007) and (iii) IL-2 (P=0.01). In contrast, blockade of the IL-10 pathway in HIV-TB coinfection did not restore MTB-specific CD4⁺ T-cell responses (d). IFN, interferon; IL, interleukin; MTB, Mycobacterium tuberculosis; TNF, tumor necrosis factor.