Skin anergy and tuberculosis

A Perspective on the Success and Failure of BCG

TB continues to be one of the major public health threats. BCG is the only available vaccine against TB and confers significant protection against the childhood disease. However, the protective efficacy of BCG against adult pulmonary TB, which represents a larger burden of disease, is highly variable. It has been suggested that prior exposure to environmental mycobacteria (EMb) mitigates the anti-TB efficacy of BCG by blocking its duplication or masking its immunogenicity. However, its effectiveness against childhood TB and failure of repeated administration to provide additional benefit against pulmonary TB, suggest of some other mechanisms for the variable efficacy of BCG against the pulmonary disease. Importantly, TB is a heterogeneous disease occurring in different forms and having distinct mechanisms of pathogenesis. While inability of the immune system to contain the bacilli is responsible for TB pathogenesis in infants, an aggravated immune response to Mtb has been blamed for the development of adult pulmonary TB. Available data suggest that EMb play a key role in heightening the immune response against Mtb. In this article, differential efficacy of BCG against childhood and adult TB is explained by taking into account the heterogeneity of TB, mechanisms of TB pathogenesis, and the effect of EMb on anti-Mtb immunity. It is believed that a refined understanding of the success and failure of BCG will help in the development of effective anti-TB vaccines.

Mesangiocapillary glomerulonephritis complicating pulmonary tuberculosis

Glomerulonephritis in tuberculosis may be a direct manifestation of renal infection or a result of immune-complex deposition complicating extra-renal infection, such as in pulmonary tuberculosis. A 17-year-old adolescent boy from Somalia was found to have pulmonary tuberculosis during routine health screening performed on entering Malta, with computed tomography of the chest showing scarring and calcification of the left upper lobe, left lower lobe consolidation, and a small left-sided pleural effusion. Five days after starting anti-tuberculous therapy, he developed lower limb and sacral oedema: urinary albumin: creatinine ratio was > 400 µg albumin/mg creatinine, and 24-h urinary protein showed nephrotic-range proteinuria of 4.963 g/day. In view of worsening lower limb, sacral and periorbital oedema and ascites, he was started on oral prednisolone, omeprazole and penicillin V prophylaxis. As heavy proteinuria persisted, a renal biopsy was performed after 8 days of prednisolone treatment, which confirmed the presence of mesangiocapillary glomerulonephritis (MCGN), with electron microscopy showing effacement of the podocytes, with hypercellularity and subendothelial immune deposits, confirming an immune-mediated pathophysiology. Ziehl-Neelsen staining did not reveal acid-fast organisms. The patient received a total of 3 weeks of oral prednisolone with subsequent tailing doses, 2 months of pyrazinamide and ethambutol and 6 months of rifampicin and isoniazid with complete resolution of his clinical and radiological signs, though heavy proteinuria persisted, so he was commenced on oral enalapril. This case highlights the potential association of MCGN with tuberculosis in adolescence. Timely recognition and treatment can prevent progression to chronic kidney disease.

IFNγ-producing CD4+ T lymphocytes: the double-edged swords in tuberculosis

IFNγ-producing CD4+ T cells (IFNγ+CD4+ T cells) are the key orchestrators of protective immunity against Mycobacterium tuberculosis (Mtb). Primarily, these cells act by enabling Mtb-infected macrophages to enforce phagosome-lysosome fusion, produce reactive nitrogen intermediates (RNIs), and activate autophagy pathways. However, TB is a heterogeneous disease and a host of clinical and experimental findings has also implicated IFNγ+CD4+ T cells in TB pathogenesis. High frequency of IFNγ+CD4+ T cells is the most invariable feature of the active disease. Active TB patients mount a heightened IFNγ+CD4+ T cell response to mycobacterial antigens and demonstrate an IFNγ-inducible transcriptomic signature. IFNγ+CD4+ T cells have also been shown to mediate TB-associated immune reconstitution inflammatory syndrome (TB-IRIS) observed in a subset of antiretroviral therapy (ART)-treated HIV- and Mtb-coinfected people. The pathological face of IFNγ+CD4+ T cells during mycobacterial infection is further uncovered by studies in the animal model of TB-IRIS and in Mtb-infected PD-1-/- mice. This manuscript encompasses the evidence supporting the dual role of IFNγ+CD4+ T cells during Mtb infection and sheds light on immune mechanisms involved in protection versus pathogenesis.

Adult pulmonary tuberculosis as a pathological manifestation of hyperactive antimycobacterial immune response

The intricate relationship between tuberculosis (TB) and immune system remains poorly understood. It is generally believed that weakening of the immune response against Mycobacterium tuberculosis leads to reactivation of latent infection into the active pulmonary disease. However, heterogeneous nature of TB and failure of rationally designed vaccines in clinical trials raises serious questions against the simplistic view of TB as an outcome of weakened immunity. In the wake of accumulating human TB data, it is argued here that a hyperactive antimycobacterial immune response is to blame for the pathogenesis of pulmonary TB in immunocompetent adults. Direct and indirect evidence supporting this notion is presented in this article. Revisiting the role of immune system in TB pathogenesis will pave the way for effective anti-TB vaccines.

Association of quantitative interferon-γ responses with the progression of naturally acquired Mycobacterium bovis infection in wild European badgers (Meles meles)

Bovine tuberculosis is one of the biggest challenges facing cattle farming in Great Britain. European badgers (Meles meles) are a reservoir host for the causal agent, Mycobacterium bovis. There have been significant recent advances in diagnostic testing for tuberculosis in humans, cattle and badgers, with the development of species-specific assays for interferon-γ (IFN-γ), an important cytokine in tuberculous infections. Using data collected from longitudinal studies of naturally infected wild badgers, we report that the magnitude of the IFN-γ response to M. bovis antigens at the disclosing test event was positively correlated with subsequent progression of disease to a seropositive or excreting state. In addition, we show that the magnitude of the IFN-γ response, despite fluctuation, declined with time after the disclosing event for all badgers, but remained significantly higher in those animals with evidence of disease progression. We discuss how our findings may be related to the immunopathogenesis of natural M. bovis infection in badgers.

Discrepancy between the tuberculin skin test and the levels of serum interferon-gamma in the diagnosis of tubercular infection in contacts

OBJECTIVE

Our aim was to compare the tuberculin skin test (TST) results and the level of serum IFN-gamma in the diagnosis of TB infection among contact of smear positive tuberculosis.

DESIGN AND METHODS

Chest x ray, tuberculin skin test and serum level of interferon-gamma (IFN-gamma) by ELISA were performed to 30 sputum positive tuberculosis patients, their 118 household contacts and 31 healthy controls.

RESULTS

The serum level of IFN-gamma was significantly elevated in index cases than in contacts and control groups. There was no statically significant difference in serum level of IFN-gamma between vaccinated and unvaccinated contacts. There was no significant correlation between IFN-gamma level and tuberculin reaction or induration diameter in vaccinated contacts. There was significant correlation between IFN-gamma level and tuberculin reaction or induration diameter in BCG unvaccinated contacts.

CONCLUSION

The serum IFN-gamma is a better indicator of the risk of mycobacterial infection than TST in BCG-vaccinated contacts.

Outbreak of bovine tuberculosis featuring anergy to the skin test, udder lesions and milkborne disease in young calves

A severe outbreak of bovine tuberculosis in a 1300-head, multisite dairy herd in Great Britain had several unusual features, including anergy to the tuberculin skin test, milkborne disease in calves and a farm cat, and a risk of human infection. The outbreak was controlled by culling 221 cattle over 15 months, by using the gamma-interferon (gamma-IFN) test and by the examination of milk samples. The gamma-IFN test detected infected animals that were not detected by the skin test.

BCG scar and positive tuberculin reaction associated with reduced child mortality in West Africa. A non-specific beneficial effect of BCG?

Previous studies have suggested that the bacille Calmette-Guérin (BCG) vaccine may have a non-specific beneficial effect on childhood survival in areas with high mortality. We examined whether BCG-vaccinated children with a BCG scar or a positive tuberculin reaction had better survival than children without such reactions. As part of an ongoing two-dose measles vaccine trial for which children were recruited at 6 months of age, we examined 1813 children for BCG scar at 6 months of age and 813 BCG-vaccinated children were skin-tested for delayed hypersensitivity to tuberculin, tetanus and diphtheria. We found that BCG-vaccinated children with a BCG scar had significantly lower mortality compared with BCG scar-negative children, the mortality ratio in the first 12 months of follow-up being 0.41 (0.25-0.67). BCG-vaccinated children with a positive tuberculin test had a mortality ratio of 0.45 (0.24-0.85) compared with tuberculin negative children. These results were unchanged by control for potential confounders or using different cut-off points for a tuberculin-positive response. Exclusion of dead children who had HIV antibodies did not modify the estimate (mortality rate (MR)=0.46 (0.23-0.94)). After censoring for tuberculosis (TB) exposure at home, the mortality ratios for having a scar and being tuberculin-positive were 0.46 (0.27-0.79) or 0.42 (0.21-0.84), respectively. Children positive to tetanus or diphtheria in the skin test had the same mortality as children not responding to these vaccine-related antigens. Thus, BCG scar and a positive tuberculin reaction were associated with better survival in early childhood in an area with high mortality. Since nothing similar was found for responders to diphtheria-tetanus-pertussis (DTP) vaccine, and the effect could not be explained by protection against tuberculosis, the effect of BCG vaccination could be due to non-specific immune-stimulation protecting against other infections.

Measurement of ultraviolet radiation-induced suppression of recall contact and delayed-type hypersensitivity in humans

This article describes methodology used for assessment of ultraviolet radiation-induced suppression of recall responses in humans. Nickel allergy is common in the general population and patch testing of nickel-allergic volunteers provides a convenient model of contact hypersensitivity. Similarly, Mantoux-positive volunteers, recruited from within hospital staff, are used as a model for delayed-type hypersensitivity. Use of secondary rather than primary immune responses allows placement of multiple test sites on each volunteer. Further, each volunteer acts as his or her own unirradiated control. This enables UV immunosuppression to be studied with relatively few human volunteers, and makes determination of UV immunosuppression dose responses feasible in human subjects. The method can also be used for assessment of the level of immune protection afforded by agents such as sunscreens or biologically active substances.

Decline in total serum IgE after treatment for tuberculosis

BACKGROUND

Infection with Mycobacterium tuberculosis induces a type-1 immune response, whereas intestinal parasites elicit a type-2 response. Given that type-1 and type-2 responses inhibit each other, we investigated if M tuberculosis downregulates serum IgE, a marker of a type-2 response.

METHODS

A prospective study was done in the Western Cape Province of South Africa, where tuberculosis and intestinal-parasite infection are common. Total serum IgE was determined for 37 controls and for 33 adolescent patients at presentation with tuberculosis and after successful completion of treatment. IgE specific for ascaris and allergens were measured in a subset of these individuals. Mantoux skin tests were done on 35 controls and on 31 patients at diagnosis.

FINDINGS

Total IgE concentrations were high in controls (mean 313 kU/L) and in patients before treatment (mean 457 kU/L, p=0.085) and declined in all patients following successful treatment (mean 175 kU/L, p<0.0001). Posttreatment IgE concentrations did not differ from concentrations in controls. Ascaris-specific IgE was lower in controls (mean 1.73 kU/L) than in patients before treatment (4.62 kU/L, p=0.023) and was 2.39 kU/L in patients after treatment (p=0.0625). Tuberculin induration correlated inversely with IgE in patients but not in controls.

INTERPRETATION

Infection with M tuberculosis as such is not incompatible with a prominent IgE response. IgE concentrations decreased after successful treatment of tuberculosis, showing that IgE concentrations in human beings can be downregulated under these circumstances, presumably due to enhancement of a type-1 response.

Concomitant HIV and mycobacterial infection in Ireland, 1987-92

A six-year retrospective review of concomitant HIV and mycobacterial infection in the Republic of Ireland is presented. A total of 42 culture proven mycobacterial infections were seen in 40 different HIV-infected patients. There were 24 infections with Mycobacterium tuberculosis (M.tb) and 18 infections with mycobacteria other than tuberculosis (MOTT), a significantly higher rate of MOTT infections in Ireland compared to a study from 1962-1981. The detection rate for all mycobacterial infections had an annual upward trend with a 4-fold increase between 1987 and 1992. In homosexuals, MOTT infections occurred more frequently than M.tb, while the reverse was true for IVDUs. Twenty per cent of the infections were seen in patients recently incarcerated. Relapse of tuberculosis occurred in 42.9% (3/7) of non-compliant patients, 2 of whom developed rifampin-resistant strains of M.tb. No patient compliant to their regimen had a relapse in disease. The overall survival of patients after diagnosis of M.tb was significantly better than those with MOTT infections, with respective one-year survival rate of 79% and 36% (log rank test, P = 0.006).