Immunopathology contributes to high mortality in tuberculous meningitis (TBM) but little is known about the blood and cerebrospinal fluid (CSF) immune response. We prospectively characterised the immune response of 160 TBM suspects in an Indonesian cohort, including 67 HIV-negative probable or definite TBM cases. TBM patients presented with severe disease and 38% died in 6 months. Blood from TBM patients analysed by flow cytometry showed lower αβT and γδT cells, NK cells and MAIT cells compared to 26 pulmonary tuberculosis patients (2.4-4-fold, all p < 0.05) and 27 healthy controls (2.7-7.6-fold, p < 0.001), but higher neutrophils and classical monocytes (2.3-3.0-fold, p < 0.001). CSF leukocyte activation was higher than in blood (1.8-9-fold). CSF of TBM patients showed a predominance of αβT and NK cells, associated with better survival. Cytokine production after ex-vivo stimulation of whole blood showed a much broader range in TBM compared to both control groups (p < 0.001). Among TBM patients, high ex-vivo production of TNF-α, IL-6 and IL-10 correlated with fever, lymphocyte count and monocyte HLA-DR expression (all p < 0.05). TBM patients show a strong myeloid blood response, with a broad variation in immune function. This may influence the response to adjuvant treatment and should be considered in future trials of host-directed therapy.

Studies in IL-32 transgenic mice and in vitro suggest that IL-32 may have protective effects against Mycobacterium tuberculosis, but so far there are barely any studies in humans. We studied the role of IL-32 and its splice variants in tuberculosis (TB) in vivo and in vitro. Blood transcriptional analysis showed lower total IL-32 mRNA levels in pulmonary TB patients compared to patients with latent TB infection and healthy controls. Also, among Indonesian household contacts who were heavily exposed to an infectious TB patient, IL-32 mRNA levels were higher among those who remained uninfected compared to those who became infected with M. tuberculosis. In peripheral blood mononuclear cells from healthy donors, we found that IL-32 , the most potent isoform, was down-regulated upon M. tuberculosis stimulation. This decrease in IL-32 was mirrored by an increase of another splice variant, IL-32 . Also, a higher IL-32 /IL-32 ratio correlated with IFN-production, whereas a lower ratio correlated with production of IL-1Ra, IL-6, and IL-17.These data suggest that IL-32 contributes to protection against M. tuberculosis infection, and that this effect may depend on the relative abundance of different IL-32 isoforms. K E Y W O R D S tuberculosis, Mycobacterium tuberculosis, immune response, interleukin-32, cytokines 1 INTRODUCTION Tuberculosis (TB) is an airborne infectious disease caused by Mycobacterium tuberculosis. TB remains a major public health problem, and approximately one-fourth of the world population is latently infected with M. tuberculosis. 1 Host factors may determine whether M. tuberculosis exposure results in infection, and whether infection progresses to disease. A comprehensive understanding of the immune response against M. tuberculosis is crucial for the development of preventive strategies. Abbreviations: IGRA, IFN-gamma release assay; TB, tuberculosis.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Background: Cellular metabolism is critical for the host immune function against pathogens, and metabolomic analysis may help understand the characteristic immunopathology of tuberculosis. We performed targeted metabolomic analyses in a large cohort of patients with tuberculous meningitis (TBM), the most severe manifestation of tuberculosis, focusing on tryptophan metabolism.Methods: We studied 1069 Indonesian and Vietnamese adults with TBM (26.6% HIV-positive), 54 non-infectious controls, 50 with bacterial meningitis, and 60 with cryptococcal meningitis. Tryptophan and downstream metabolites were measured in cerebrospinal fluid (CSF) and plasma using targeted liquid chromatography mass-spectrometry. Individual metabolite levels were associated with survival, clinical parameters, CSF bacterial load and 92 CSF inflammatory proteins.Results: CSF tryptophan was associated with 60-day mortality from tuberculous meningitis (HR=1.16, 95%CI=1.10-1.24, for each doubling in CSF tryptophan) both in HIV-negative and HIV-positive patients. CSF tryptophan concentrations did not correlate with CSF bacterial load nor CSF inflammation but were negatively correlated with CSF interferon-gamma concentrations. Unlike tryptophan, CSF concentrations of an intercorrelating cluster of downstream kynurenine metabolites did not predict mortality. These CSF kynurenine metabolites did however correlate with CSF inflammation and markers of blood-CSF leakage, and plasma kynurenine predicted death (HR 1.54, 95%CI=1.22-1.93). These findings were mostly specific for TBM, although high CSF tryptophan was also associated with mortality from cryptococcal meningitis.Conclusion: TBM patients with a high baseline CSF tryptophan or high systemic (plasma) kynurenine are at increased risk of death. These findings may reveal new targets for host-directed therapy.Funding: This study was supported by National Institutes of Health (R01AI145781) and the Wellcome Trust (110179/Z/15/Z and 206724/Z/17/Z).