Immune function in young children with previous pulmonary or miliary/meningeal tuberculosis and impact of BCG vaccination

Tuberculosis susceptibility and protection in children

Children represent both a clinically important population susceptible to tuberculosis and a key group in whom to study intrinsic and vaccine-induced mechanisms of protection. After exposure to Mycobacterium tuberculosis, children aged under 5 years are at high risk of progressing first to tuberculosis infection, then to tuberculosis disease and possibly disseminated forms of tuberculosis, with accompanying high risks of morbidity and mortality. Children aged 5-10 years are somewhat protected, until risk increases again in adolescence. Furthermore, neonatal BCG programmes show the clearest proven benefit of vaccination against tuberculosis. Case-control comparisons from key cohorts, which recruited more than 15 000 children and adolescents in total, have identified that the ratio of monocytes to lymphocytes, activated CD4 T cell count, and a blood RNA signature could be correlates of risk for developing tuberculosis. Further studies of protected and susceptible populations are necessary to guide development of novel tuberculosis vaccines that could facilitate the achievement of WHO's goal to eliminate deaths from tuberculosis in childhood.

Altered cytokine profiles in children with indeterminate quantiferon results and common infections

OBJECTIVES

An increased rate of indeterminate quantiferon results (low IFN-γ release in the phytohemagglutinin-stimulated tube) has been reported in children with clinical signs compatible with tuberculosis but with the final diagnosis of infectious diseases different from tuberculosis. Here, we addressed the mechanisms involved and assessed potential alternative biomarkers to overcome indeterminate quantiferon results under these conditions.

METHODS

Cytokine concentrations were measured in residual plasma from quantiferon assays performed in immunocompetent children (cases, median age: 3 years 9 months) with indeterminate results and community acquired pneumonia (n = 7) or meningoencephalitis (n = 1). Controls were age-matched immunocompetent children with determinate quantiferon results (infected with mycobacterium tuberculosis, n = 7 or not, n = 8).

RESULTS

Lower IFN-γ expression in phytohemagglutinin-stimulated cultures from cases was accompanied by lower Th1 (IL-2, TNF-α, IP-10) and Th2 (IL-5, IL-13), but similar IL-10 secretion capacities as the controls.

CONCLUSIONS

A state of hyporesponsiveness that resembles the concept of immunoparalysis in severe infection was observed in children with milder infections. Though IP-10, IL-2, IL-5 and IL-13 were confirmed as promising alternative biomarkers for discriminating controls with and without tuberculosis in this study, defective induction of these biomarkers by phytohemagglutinin in cases precluded their usefulness in overcoming quantiferon indeterminate results in the above-mentioned clinical conditions.

Modeling tuberculous meningitis in zebrafish using Mycobacterium marinum

Tuberculous meningitis (TBM) is one of the most severe extrapulmonary manifestations of tuberculosis, with a high morbidity and mortality. Characteristic pathological features of TBM are Rich foci, i.e. brain- and spinal-cord-specific granulomas formed after hematogenous spread of pulmonary tuberculosis. Little is known about the early pathogenesis of TBM and the role of Rich foci. We have adapted the zebrafish model of Mycobacterium marinum infection (zebrafish-M. marinum model) to study TBM. First, we analyzed whether TBM occurs in adult zebrafish and showed that intraperitoneal infection resulted in granuloma formation in the meninges in 20% of the cases, with occasional brain parenchyma involvement. In zebrafish embryos, bacterial infiltration and clustering of infected phagocytes was observed after infection at three different inoculation sites: parenchyma, hindbrain ventricle and caudal vein. Infection via the bloodstream resulted in the formation of early granulomas in brain tissue in 70% of the cases. In these zebrafish embryos, infiltrates were located in the proximity of blood vessels. Interestingly, no differences were observed when embryos were infected before or after early formation of the blood-brain barrier (BBB), indicating that bacteria are able to cross this barrier with relatively high efficiency. In agreement with this observation, infected zebrafish larvae also showed infiltration of the brain tissue. Upon infection of embryos with an M. marinum ESX-1 mutant, only small clusters and scattered isolated phagocytes with high bacterial loads were present in the brain tissue. In conclusion, our adapted zebrafish-M. marinum infection model for studying granuloma formation in the brain will allow for the detailed analysis of both bacterial and host factors involved in TBM. It will help solve longstanding questions on the role of Rich foci and potentially contribute to the development of better diagnostic tools and therapeutics.

Increased severity of tuberculosis in Guinea pigs with type 2 diabetes: a model of diabetes-tuberculosis comorbidity

Impaired glucose tolerance and type 2 diabetes were induced in guinea pigs to model the emerging comorbidity of Mycobacterium tuberculosis infection in diabetic patients. Type 2 diabetes mellitus was induced by low-dose streptozotocin in guinea pigs rendered glucose intolerant by first feeding a high-fat, high-carbohydrate diet before M. tuberculosis exposure. M. tuberculosis infection of diabetic guinea pigs resulted in severe and rapidly progressive tuberculosis (TB) with a shortened survival interval, more severe pulmonary and extrapulmonary pathology, and a higher bacterial burden compared with glucose-intolerant and nondiabetic controls. Compared with nondiabetics, diabetic guinea pigs with TB had an exacerbated proinflammatory response with more severe granulocytic inflammation and higher gene expression for the cytokines/chemokines interferon-γ, IL-17A, IL-8, and IL-10 in the lung and for interferon-γ, tumor necrosis factor-α, IL-8, and monocyte chemoattractant protein-1 in the spleen. TB disease progression in guinea pigs with impaired glucose tolerance was similar to that of nondiabetic controls in the early stages of infection but was more severe by day 90. The guinea pig model of type 2 diabetes-TB comorbidity mimics important features of the naturally occurring disease in humans. This model will be beneficial in understanding the complex pathogenesis of TB in diabetic patients and to test new strategies to improve TB and diabetes control when the two diseases occur together.

Tuberculous meningitis

Tuberculous (TB) meningitis is common in resource-poor communities but also occurs in developed countries where the diagnosis is frequently delayed because of unfamiliarity with the disease. TB meningitis develops whenever a small intracranial tuberculoma (Rich focus) ruptures causing predominantly basal meningitis. This results in hydrocephalus, cranial nerve palsies, and ischemic brain injury secondary to tuberculous vasculitis. The primary source of TB is usually the lung. Early diagnosis is difficult because patients tend to present subacutely with nonspecific symptoms such as fever, cough, vomiting, listlessness, and failure to thrive. Lumbar puncture typically shows clear and colorless CSF with a low, predominantly lymphocytic, leukocytosis and raised protein and low glucose levels. Decision to treat is mostly clinical because of difficulty in demonstrating TB bacilli on routine smear and time needed for culture. A positive TB contact, Mantoux skin test, chest radiograph, CT/MRI brain scan, PCR for tuberculosis on CSF, and demonstration of TB bacilli from extraneural sources are invaluable in supporting a diagnosis of TB meningitis. Current World Health Organization guidelines recommend treatment with a four-drug regimen for 2 months, followed by a two-drug regimen for 10 months, the total duration of treatment being 12 months. Corticosteroids reduce mortality without changing neurological morbidity. Outcome relates closely to age and stage of disease.

BCG vaccination is associated with decreased severity of tuberculosis in Pakistan

Vaccination with Bacille Calmette-Guérin (BCG) is given at birth to protect against tuberculosis (TB) in Pakistan. The country ranks 6th amongst high-burden countries worldwide and has an incidence of 231/100,000 pyopulation. This was a cross-sectional multi-center hospital-based study. TB patients (n=218) with pulmonary (PTB, n=120) or extrapulmonary (ETB, 98) were recruited, and the presence of a BCG vaccination scar was documented. Cases were further classified into minimal, moderate and advanced PTB or less severe (L-ETB) or severe disseminated (D-ETB) disease. The association of age, gender and severity of TB infections with BCG vaccination of the individual TB cases was investigated. No difference was found of the BCG vaccination status of PTB and ETB cases, or in relation to age or gender. Patients under 29years of age comprised the largest group. There were more females with ETB than PTB. The largest group within ETB comprised those with tuberculous lymphadenitis (LNTB, 39%). A significantly greater number of LNTB cases had received BCG vaccinations than had those with pleural (unilateral) TB (p=0.004), and tuberculous meningitis (p=0.027) groups. Also, there were more immunized patients with pulmonary as compared with pleural disease (p=0.001). LNTB represents localized granulomatous disease and the observation of higher vaccination rates in this group suggests that BCG has protected against more severe forms of TB in this high-burden region.

Abnormal immune responses in persons with previous extrapulmonary tuberculosis in an in vitro model that simulates in vivo infection with Mycobacterium tuberculosis

Persons with previous extrapulmonary tuberculosis have reduced peripheral blood mononuclear cell cytokine production and CD4(+) lymphocytes compared to persons with previous pulmonary tuberculosis or latent tuberculosis infection, but specific defects related to Mycobacterium tuberculosis infection of macrophages have not been characterized. The objective of this study was to further characterize the in vitro immune responses to M. tuberculosis infection in HIV-seronegative persons with previous extrapulmonary tuberculosis. Peripheral blood mononuclear cells were isolated from HIV-seronegative persons with previous extrapulmonary tuberculosis (n = 11), previous pulmonary tuberculosis (n = 21), latent M. tuberculosis infection (n = 19), and uninfected tuberculosis contacts (n = 20). Experimental conditions included M. tuberculosis-infected macrophages cultured with and without monocyte-depleted peripheral blood mononuclear cells. Concentrations of interleukin 1β (IL-1β), IL-4, IL-6, CXCL8 (IL-8), IL-10, IL-12p70, IL-17, CCL2 (monocyte chemoattractant protein 1), tumor necrosis factor alpha (TNF-α), and gamma interferon (IFN-γ) were measured by multiplex cytokine array. When M. tuberculosis-infected macrophages were cocultured with monocyte-depleted peripheral blood mononuclear cells, IFN-γ (P = 0.01), TNF-α (P = 0.04), IL-10 (P < 0.001), and IL-6 (P = 0.03) exhibited similar continua of responses, with uninfected persons producing the lowest levels, followed by extrapulmonary tuberculosis cases, pulmonary tuberculosis controls, and persons with latent M. tuberculosis infection. A similar pattern was observed with CXCL8 (P = 0.04), IL-10 (P = 0.02), and CCL2 (P = 0.03) when monocyte-depleted peripheral blood mononuclear cells from the four groups were cultured alone. Persons with previous extrapulmonary tuberculosis had decreased production of several cytokines, both at rest and after stimulation with M. tuberculosis. Our results suggest that persons who develop extrapulmonary tuberculosis have a subtle global immune defect that affects their response to M. tuberculosis infection.

Tuberculous meningitis in Bacille Calmette-Guerin-vaccinated children: clinical spectrum and outcome

The Bacille Calmette-Guérin vaccination (BCG) contributed widely to reduce tuberculosis incidence in developing countries. The aim of this report was to assess the clinical "spectrum" and outcome of tuberculous meningitis in 16 Bacille Calmette-Guérin-vaccinated Tunisian children. They were 9 boys and 7 girls aged 2 to 168 months (median 72 months ± 65.88). Patients presented mainly with nonspecific symptoms. Neurologic severity was classified as grade I (n = 6) and grade II or III (n = 10). At short-term course, the majority of patients developed serious complications: hydrocephalus (n = 12), seizures (n = 8), tuberculoma (n = 6), and acute respiratory failure (n = 2). Three patients died. Among survivors, 4 patients showed a complete recovery while 9 developed permanent sequelae which were mild (n = 6) to severe (n = 3). Despite the Bacille Calmette-Guérin vaccination, tuberculous meningitis remains a life-threatening condition; vaccinated children have shown common presentation of tuberculous meningitis in terms of severity and poor outcome.

Electrochemiluminescence in bioanalysis

The discovery of electrochemiluminescence (ECL) and its development as a means of detection is truly a success story. Although studies describing ECL were published in the early 1960s, most studies using ECL as a means of detection were not widely published until the mid 1990s. Incorporating ECL into assays provides increased sensitivity, several logs of dynamic range and the ability to electronically control the reaction. These characteristics provide advantages over assays that rely on radioisotopic labels, fluorescence and enzymatic activity. There have been many areas of science that have benefited from the use of ECL, including environmental microbiology, virology, neurobiology, molecular biology and immunology. ECL has improved the understanding and treatment of infectious diseases, cancer, neurodegenerative diseases and even sleep apnea disorders. Drug development has also benefited from ECL via improved assessment of pharmacodynamics, pharmacokinetics and determining immune responses against protein-based therapeutics. This review provides an overview of ECL chemistry and principles with a more detailed emphasis on the applications of ECL-based assays in different areas of science and medicine. The primary purpose of this review is to provide an in-depth discussion of the impact that ECL-based analysis has had on microbiology, immunology, virology, neurodegenerative diseases, molecular biology and drug development. Examples of ECL-based bioanalysis in each of these fields are discussed in conjunction with an overview of ECL principles and instrumentation.

Interferon-gamma +874 T/A and interleukin-10 -1082 A/G single nucleotide polymorphism in Egyptian children with tuberculosis

The aim was to investigate the association of interferon-gamma (IFN-γ) +874 T/A and interleukin-10 (IL-10)-1082 A/G single nucleotide polymorphisms with tuberculous infection and post-BCG lymphadenitis in Egyptian children. IFN-γ +874 T/A and IL-10 -1082 A/G polymorphism detection by amplification refractory mutation system technique was carried out for 110 patients with TB, 40 patients with post-BCG lymphadenitis and 118 healthy controls. IFN-γ +874 A allele was higher in TB and post-BCG patients than those in healthy controls (Pc=0.006 and 0.002, respectively). IFN-γ +874 genotype AA was significantly higher in patients with TB than that in control (Pc=0.015), in extrapulmonary than patients with pulmonary TB (PTB) (Pc=0.009), and young children with TB below 5 years (Pc=0.024). No statistically significant differences were observed between patients with TB and controls for the frequency of IL-10(-1082) alleles or genotypes (P>0.05); however, a statistically significant difference in the frequency of IL-10 (-1082) GG genotype was found between patients with pulmonary and extrapulmonary TB (Pc=0.003). Low producer IFN-γ +874 A/A genotype is associated with post-BCG lymphadenitis and TB disease especially in younger children below 5 years. IL-10-1082 G/G genotype did not exhibit significant association except for increased GG frequency in PTB. Both cytokine polymorphisms have no relation to tuberculin reaction in patients with TB.

Tuberculous meningitis

Tuberculous meningitis is a severe form of extrapulmonary tuberculosis. The exact incidence and prevalence are not known. In countries with high burden of pulmonary tuberculosis, the incidence is expected to be proportionately high. Children are much more vulnerable. Human immunodeficiency virus-infected patients have a high incidence of tuberculous meningitis. The hallmark pathological processes are meningeal inflammation, basal exudates, vasculitis and hydrocephalus. Headache, vomiting, meningeal signs, focal deficits, vision loss, cranial nerve palsies and raised intracranial pressure are dominant clinical features. Diagnosis is based on the characteristic clinical picture, neuroimaging abnormalities and cerebrospinal fluid changes (increased protein, low glucose and mononuclear cell pleocytosis). Cerebrospinal fluid smear examination, mycobacterial culture or polymerase chain reaction is mandatory for bacteriological confirmation. The mortality and morbidity of tuberculous meningitis are exceptionally high. Prompt diagnosis and early treatment are crucial. Decision to start antituberculous treatment is often empirical. WHO guidelines recommend a 6 months course of antituberculous treatment; however, other guidelines recommend a prolonged treatment extended to 9 or 12 months. Corticosteroids reduce the number of deaths. Resistance to antituberculous drugs is associated with a high mortality. Patients with hydrocephalus may need ventriculo-peritoneal shunting. Bacillus Calmette-Guérin vaccination protects to some degree against tuberculous meningitis in children.

CCL2 responses to Mycobacterium tuberculosis are associated with disease severity in tuberculosis

Background

Leucocyte activating chemokines such as CCL2, CCL3, and CXCL8 together with proinflammatory IFNγ, TNFα and downmodulatory IL10 play a central role in the restriction of M. tuberculosis infections, but is unclear whether these markers are indicative of tuberculosis disease severity.

Methodology

We investigated live M. tuberculosis- and M. bovis BCG- induced peripheral blood mononuclear cell responses in patients with tuberculosis (TB) and healthy endemic controls (ECs, n = 36). TB patients comprised pulmonary (PTB, n = 34) and extrapulmonary groups, subdivided into those with less severe localized extrapulmonary TB (L-ETB, n = 16) or severe disseminated ETB (D-ETB, n = 16). Secretion of CCL2, IFNγ, IL10 and CCL3, and mRNA expression of CCL2, TNFα, CCL3 and CXCL8 were determined.

Results

M. tuberculosis- and BCG- induced CCL2 secretion was significantly increased in both PTB and D-ETB (p<0.05, p<0.01) as compared with L-ETB patients. CCL2 secretion in response to M. tuberculosis was significantly greater than to BCG in the PTB and D-ETB groups. M. tuberculosis-induced CCL2 mRNA transcription was greater in PTB than L-ETB (p = 0.023), while CCL2 was reduced in L-ETB as compared with D-ETB (p = 0.005) patients. M. tuberculosis –induced IFNγ was greater in L-ETB than PTB (p = 0.04), while BCG-induced IFNγ was greater in L-ETB as compared with D-ETB patients (p = 0.036). TNFα mRNA expression was raised in PTB as compared with L-ETB group in response to M. tuberculosis (p = 0.02) and BCG (p = 0.03). Mycobacterium-induced CCL3 and CXCL8 was comparable between TB groups.

Conclusions

The increased CCL2 and TNFα in PTB patients may support effective leucocyte recruitment and M. tuberculosis localization. CCL2 alone is associated with severity of TB, possibly due to increased systemic inflammation found in severe disseminated TB or due to increased monocyte infiltration to lung parenchyma in pulmonary disease.