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

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. Copyright: © 2013 Goovaerts et al.

The neuropeptide pituitary adenylate cyclase activating protein stimulates human monocytes by transactivation of the Trk/NGF pathway.

Transactivation is a process whereby stimulation of G-protein-coupled receptors (GPCR) activates signaling from receptors tyrosine kinase (RTK). In neuronal cells, the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) acting through the GPCR VPAC-1 exerts trophic effects by transactivating the RTK TrkA receptor for the nerve growth factor (NGF). Both PACAP and NGF have pro-inflammatory activities on monocytes. We have tested the possibility that in monocytes, PACAP, as reported in neuronal cells, uses NGF/TrkA signaling pathway. In these cells, PACAP increases TrkA tyrosine phosphorylations through a PI-3kinase dependent but phospholipase C independent pathway. K252a, an inhibitor of TrkA decreases PACAP-induced Akt and ERK phosphorylation and calcium mobilisation resulting in decreases in intracellular H2O2 production and membrane upregulation of CD11b expression, both functions being inhibited after anti-NGF or anti-TrkA antibody treatment. K252a also inhibits PACAP-associated NF-KB activity. Monocytes increase in NGF production is seen after micromolar PACAP exposure while nanomolar treatment which desensitizes cells to high dose of PACAP prevents PACAP-induced TrkA phosphorylation, H2O2 production and CD11b expression. Finally, NGF-dependent ERK activation and H2O2 production is pertussis toxin sensitive. Altogether these data indicate that in PACAP-activated monocytes some pro-inflammatory activities occur through transactivation mechanisms involving VPAC-1, NGF and TrkA-associated tyrosine kinase activity.