LPS-binding protein and IL-6 mark paradoxical tuberculosis immune reconstitution inflammatory syndrome in HIV patients

Abstract

Background: Tuberculosis-associated immune reconstitution inflammatory syndrome (TB-IRIS) remains a poorly understood complication in HIV-TB co-infected patients initiating antiretroviral therapy (ART). The role of the innate immune system in TB-IRIS is becoming increasingly apparent, however the potential involvement in TB-IRIS of a leaky gut and proteins that interfere with TLR stimulation by binding PAMPs has not been investigated before. Here we aimed to investigate the innate nature of the cytokine response in TB-IRIS and to identify novel potential biomarkers.

Methods: From a large prospective cohort of HIV-TB co-infected patients receiving TB treatment, we compared 40 patients who developed TB-IRIS during the first month of ART with 40 patients matched for age, sex and baseline CD4 count who did not. We analyzed plasma levels of lipopolysaccharide (LPS)-binding protein (LBP), LPS, sCD14, endotoxin-core antibody, intestinal fatty acid-binding protein (I-FABP) and 18 pro-and anti-inflammatory cytokines before and during ART.

Results: We observed lower baseline levels of IL-6 (p = 0.041), GCSF (p = 0.036) and LBP (p = 0.016) in TB-IRIS patients. At IRIS event, we detected higher levels of LBP, IL-1RA, IL-4, IL-6, IL-7, IL-8, G-CSF (p ≤ 0.032) and lower I-FABP levels (p = 0.013) compared to HIV-TB co-infected controls. Only IL-6 showed an independent effect in multivariate models containing significant cytokines from pre-ART (p = 0.039) and during TB-IRIS (p = 0.034).

Conclusion: We report pre-ART IL-6 and LBP levels as well as IL-6, LBP and I-FABP levels during IRIS-event as potential biomarkers in TB-IRIS. Our results show no evidence of the possible contribution of a leaky gut to TB-IRIS and indicate that IL-6 holds a distinct role in the disturbed innate cytokine profile before and during TB-IRIS. Future clinical studies should investigate the importance and clinical relevance of these markers for the diagnosis and treatment of TB-IRIS.

Figure 1. Markers of a leaky gut in TB-IRIS patients and controls during follow-up.

Horizontal lines represent median plasma levels for each patient group at each time point. A Wilcoxon signed-rank test was used to calculate p values. The level of significance was set to p < 0.05. Dotted lines indicate significant changes over time per patient-group and full lines indicate significant differences between matched patients. (A) EndoCab. Number of patients in each group during consecutive time points is 35, 35, 30 and 29 respectively. (B) I-FABP. Number of patients in each group during consecutive time points is 38, 38, 32 and 31 respectively. (C) LPS. Number of patients in each group during consecutive time points is 11 and 13 respectively. GMU, IgG median units; EU, endotoxin units.

Figure 2. LBP and sCD14 plasma levels in TB-IRIS patients and controls during follow-up.

Horizontal lines represent median levels of LBP (A) and sCD14 (B) for each patient group at each time point. A Wilcoxon signed-rank test was used to calculate p values. The level of significance was set to p < 0.05. Dotted lines indicate significant changes over time per patient-group and full lines indicate significant differences between matched patients. Number of patients in each group during consecutive time points is 38, 38, 32 and 31 respectively.