Peripheral Blood Gamma Interferon Release Assays Predict Lung Responses andMycobacterium tuberculosisDisease Outcome in Mice

Abstract

Current diagnostic tests for tuberculosis (TB) are not able to distinguish active disease from latent Mycobacterium tuberculosis infection, nor are they able to quantify the risk of a latently infected person progressing to active TB. There is interest, however, in adapting antigen-specific gamma interferon (IFN-␥) release assays (IGRAs) to predict disease outcome. In this study, we used the differential susceptibilities of inbred mouse strains to M. tuberculosis infection to evaluate the prognostic capabilities of IGRAs. Using lung and blood cultures, we determined that CBA/J, DBA/2, and C3H/HeJ mice (models of heightened risk of progression to active TB) produced less antigen-specific IFN-␥ in response to M. tuberculosis culture filtrate proteins and early secreted antigenic target-6 than the relatively resistant C57BL/6 mouse strain. Additionally, reduced IFN-␥ secretion in supernatants reflected a reduced frequency of IFN-␥-responding cells in the lung and blood and not a specific defect in IFN-␥ secretion at the single-cell level. Importantly, detection of antigen-specific IFN-␥ from blood cultures accurately reflected lung responses, indicating that blood can be an appropriate test tissue in humans. Furthermore, reduced antigen-specific IFN-␥ production and low frequencies of IFN-␥-responding cells from peripheral blood predicted increased risk of TB disease progression across genetically diverse TB disease-susceptible mouse strains, suggesting that similar results may occur in humans. The development of efficacious predictive diagnostic tests for humans would lead to targeted therapy prior to progression to active TB, reducing transmission, incidence, and prevalence rates while maximizing the use of public health resources.Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), infects up to one-third of the world's population (60). The majority (90%) of infected adults control M. tuberculosis in a latent state that is clinically silent and is not considered contagious. In contrast, the remaining 10% of M. tuberculosis-infected individuals progress to contagious, active TB and may transmit bacilli to others, resulting in significant global morbidity and mortality each year (61). The mechanisms that contribute to M. tuberculosis susceptibility and TB disease progression in humans are multifactorial and reflect altered pulmonary immunity due to polygenic interactions, immune status, age, and environmental factors (6, 50). These interactions contribute to the common outcome of active TB, associated with increased growth of M. tuberculosis in the lung and detrimental pulmonary inflammation, for which similar disease characteristics have been described in animal models (4,12,54).Although the predisposing mechanisms underlying progression to active TB are not fully understood, we and others (1,36,41) propose that the transition from latency to active TB can be detected, quantified, and predicted by peripheral immune responses prior to disease onset. The identification of such biomarkers could then...

Diagnosing TB infection in children: analysis of discordances using in vitro tests and the tuberculin skin test

“…TB infection control in animals and humans is associated with the production of IFN-c by the CD4+ T-helper (Th)-cells [39]. It has been shown, in animal models, that a decreased production of IFN-c and a decrease in the number of IFN-c-producing cells are predictive of an increased risk of developing TB [40]. In contact patients, it has been observed that the progression to disease was associated with a decrease in IFN-c, and an increase in interleukin (IL)-10 and IL-4 levels [41,42].…”

Tuberculosis in CBA/J Mice

“…24,30,33 We use CBA/J mice to model pulmonary TB because these mice have no known immunological defects, are relatively susceptible to M.tb infection, and maintain long-term stable M.tb burdens. 2,3,36 Yet, the manifestation of TB disease in CBA/J mice has not been completely described. Here, we show microscopic features of TB disease in CBA/J mice and in M.tb-infected CBA/J mice that have no clinical signs.…”

“…In some experiments, mice were euthanized when 10% of their peak body weight was lost and there were no other clinical signs. The M.tb pulmonary burden was calculated by colonyforming units as previously described 3 or lungs were fixed in 10% neutral buffered formalin for hematoxylin and eosin (HE), Masson's trichrome, Von Kossa, or modified ZiehlNeelsen acid-fast staining. Slides were evaluated by a boardcertified veterinary pathologist (G. Beamer) and scanned at 40Â using an Aperio ScanScope (Aperio, Vista, CA).…”

“…Mice were infected with M.tb by aerosol exposure and weighed weekly throughout M.tb infection, as previously described. 3 Mice were euthanized when all of the following IACUC removal criteria were met: weight loss of 20%, unthrifty hair coat, social isolation, and tachypnea or dyspnea. In some experiments, mice were euthanized when 10% of their peak body weight was lost and there were no other clinical signs.…”

Biomarkers for risk of developing active tuberculosis in contacts of TB patients: a prospective cohort study

“…people with HIV infection). Screening for the individuals most at risk of developing active TB from the huge "at-risk" reservoir of LTBI cases is an important goal of TB control efforts worldwide [6]. The prevalence of LTBI in close TB contacts is reported to be high: being a household contact is a serious risk factor associated with progression to active TB [7,8].…”