Differential requirement for interferon-gamma to restrict the growth of or eliminate some recently identified species of nontuberculous mycobacteria in vivo

Mycobacterium interjectum Lung Infection

A 62-year-old male presented with productive cough, weight loss, and night sweats. CXR revealed a right upper lobe cavitary lesion. Evaluation was negative for Mycobacterium tuberculosis, and sputum revealed Mycobacterium avium intracellulare (MAI). Since his clinical course was atypical for MAI, further investigations were pursued which identified Mycobacterium interjectum in lung specimens, a very rarely described etiology of pulmonary disease. Appropriate therapy with rifampin, intravenous amikacin, trimethoprim/sulfamethoxazole (TMP/SMX), and ethambutol resulted in clinical and radiographic improvement. This is the third case described over a period of 20 years of destructive lung disease in an immunocompetent adult due to M. interjectum.

Disseminated Mycobacterium avium intracellulare infection in an "immunocompetent" host

We are reporting the case of a 37-year-old immunocompetent patient who presented with anterior chest wall swelling, jaw swelling and pain, back pain, night sweats, and unintentional weight loss. He underwent mediastinoscopy with lymph node biopsy, which revealed caseating and noncaseating granuloma and special stains positive for acid-fast bacteria. Cultures from two different sites surprisingly grew Mycobacterium avium intercellulare (MAI), and a diagnosis of disseminated MAI was made. He was switched from antituberculous treatment to MAI treatment.

Host immune response to rapidly growing mycobacteria, an emerging cause of chronic lung disease

Rapidly growing mycobacteria (RGM) are environmental organisms classified under the broader category of nontuberculous mycobacteria. The most common RGM to cause human diseases are Mycobacterium abscessus, Mycobacterium chelonae, Mycobacterium fortuitum, and Mycobacterium massiliense. Infections due to the RGM are an emerging health problem in the United States. Chronic pulmonary disease and skin/soft-tissue infections are the two most common disorders due to these organisms. Clinical outcomes in the treatment of M. abscessus infections are generally disappointing. Because less is known about the nature of the immune response to M. abscessus than for tuberculosis, we herein highlight the major clinical features associated with infections due to M. abscessus and other RGM, and review the known host immune response to RGM, drawing from experimental animal and clinical studies. Based on in vitro and in vivo murine models, Toll-like receptor 2, dectin-1, tumor necrosis factor (TNF)-α, IFN-γ, leptin, T cells, and possibly neutrophils are important components in the host defense against RGM infections. However, excessive induction of TNF-α by the R morphotype of M. abscessus may allow it to be more pathogenic than the S morphotype. Clinical observations and/or genetic studies in humans corroborate many of the findings in animals in that those with cell-mediated immunodeficiency, genetic defects in IFN-γ-IL-12 axis, and those individuals on TNF-α blockers are at increased risk for nontuberculous mycobacteria infections, including the RGM. However, much remains to be discovered on why seemingly healthy individuals, particularly slender postmenopausal women with thoracic cage anomalies, appear to be at increased risk.

Infections due to various atypical mycobacteria in a Norwegian multiplex family with dominant interferon-gamma receptor deficiency

BACKGROUND

Atypical mycobacteria can cause systemic infections in patients with certain types of immunodeficiency.

METHODS

Clinical samples were decontaminated and cultured to assess the presence of mycobacterial species. Gene sequencing was performed to reveal interferon-gamma receptor 1 (IFN-gamma R1) deficiency.

RESULTS

The index patient received a diagnosis of dominant IFN-gamma R1 deficiency during treatment for a serious infection due to atypical mycobacteria. She belongs to a Norwegian multiplex family comprising 3 generations and 5 patients with dominant IFN-gamma R1 deficiency. Four of these patients have been treated with tuberculostatics because of extensive infection due to atypical mycobacteria, such as Mycobacterium avium-intracellulare, Mycobacterium scrofulaceum, Mycobacterium bovis (bacille Calmette-Guérin), Mycobacterium bohemicum, and Mycobacterium gordonae. Two of the patients have also received subcutaneous injections of IFN-gamma. One family member with the deficiency has not received treatment and is still healthy at 13 years of age.

CONCLUSIONS

Serious infection due to atypical mycobacteria should initiate a search for primary immunodeficiencies, particularly IFN-gamma R1 deficiency. Treatment with IFN-gamma should be started when serious infection due to atypical mycobacteria is verified and dominant partial IFN-gamma R1 deficiency is suspected.

IFN-gamma mediates the rejection of haematopoietic stem cells in IFN-gammaR1-deficient hosts

BACKGROUND

Interferon-gamma receptor 1 (IFN-gammaR1) deficiency is a life-threatening inherited disorder, conferring predisposition to mycobacterial diseases. Haematopoietic stem cell transplantation (HSCT) is the only curative treatment available, but is hampered by a very high rate of graft rejection, even with intra-familial HLA-identical transplants. This high rejection rate is not seen in any other congenital disorders and remains unexplained. We studied the underlying mechanism in a mouse model of HSCT for IFN-gammaR1 deficiency.

METHODS AND FINDINGS

We demonstrated that HSCT with cells from a syngenic C57BL/6 Ifngr1+/+ donor engrafted well and restored anti-mycobacterial immunity in naive, non-infected C57BL/6 Ifngr1-/- recipients. However, Ifngr1-/- mice previously infected with Mycobacterium bovis bacillus Calmette-Guérin (BCG) rejected HSCT. Like infected IFN-gammaR1-deficient humans, infected Ifngr1-/- mice displayed very high serum IFN-gamma levels before HSCT. The administration of a recombinant IFN-gamma-expressing AAV vector to Ifngr1-/- naive recipients also resulted in HSCT graft rejection. Transplantation was successful in Ifngr1-/- x Ifng-/- double-mutant mice, even after BCG infection. Finally, efficient antibody-mediated IFN-gamma depletion in infected Ifngr1-/- mice in vivo allowed subsequent engraftment.

CONCLUSIONS

High serum IFN-gamma concentration is both necessary and sufficient for graft rejection in IFN-gammaR1-deficient mice, inhibiting the development of heterologous, IFN-gammaR1-expressing, haematopoietic cell lineages. These results confirm that IFN-gamma is an anti-haematopoietic cytokine in vivo. They also pave the way for HSCT management in IFN-gammaR1-deficient patients through IFN-gamma depletion from the blood. They further raise the possibility that depleting IFN-gamma may improve engraftment in other settings, such as HSCT from a haplo-identical or unrelated donor.

Importance of T cells, gamma interferon, and tumor necrosis factor in immune control of the rapid grower Mycobacterium abscessus in C57BL/6 mice

Mycobacterium abscessus is an emerging rapidly growing mycobacterium that causes tuberculous-like lesions in humans. We studied the immune control of this organism in C57BL/6 mice challenged intravenously with 10(7) CFU. Bacteria were eliminated from both the spleen and the liver within 90 days, and liver histology showed organized granulomatous lesions. A T- and B-cell requirement was investigated by challenging Rag2-/-, Cd3epsilon-/-, and muMT-/- mice. Rag2-/- and Cd3epsilon-/- mice were significantly impaired in the ability to clear M. abscessus from the liver and spleen, and muMT-/- mice were significantly impaired in the ability to clear M. abscessus from the liver, suggesting that infection control was primarily T cell dependent in the spleen and both T and B cell dependent in the liver. The liver granulomatous response was similar to that of wild-type controls in muMT-/- mice but completely absent in Cd3epsilon-/- and Rag2-/- mice. We studied the involvement of gamma interferon (IFN-gamma) and tumor necrosis factor (TNF) by challenging C57BL/6 mice deficient in the IFN-gamma receptor (Ifngr1-/-) and in TNF (Tnf-/-). Ifngr1-/- mice were significantly impaired in M. abscessus control both in the spleen and in the liver, and granulomas were profoundly altered. The effect was even more substantial in Tnf-/- mice; they failed to control M. abscessus infection in the liver and died within 20 to 25 days after infection with many hepatic inflammatory foci and major lesions of ischemic necrosis in the liver and kidney. These features were not observed with the closely related species M. chelonae. T-cell immunity, IFN-gamma, and TNF are central factors for the control of M. abscessus in C57BL/6 mice, as they are for the control of pathogenic slowly growing mycobacteria.

Mycobacterium lentiflavum, an emerging pathogen?

Three cases of infection due to Mycobacterium lentiflavum, a recently described species characterized by multiple resistance to anti-mycobacterial drugs, are reported here. While one case simply adds to the number of cervical lynphadenitis reported in literature, the others concern the first isolations from pleural effusions, in a young boy with leukaemia and in an elderly patient with lung disease, respectively.

Contribution of NK, NK T, gamma delta T, and alpha beta T cells to the gamma interferon response required for liver protection against Trypanosoma cruzi

In the present work, we show that intracellular Trypanosoma cruzi is rarely found in the livers of acutely infected mice, but inflammation is commonly observed. The presence of numerous intrahepatic amastigotes in infected gamma interferon (IFN-gamma)-deficient mice corroborates the notion that the liver is protected by an efficient local immunity. The contribution of different cell populations was suggested by data showing that CD4- and CD8-deficient mice were able to restrain liver parasite growth. Therefore, we have characterized the liver-infiltrating lymphocytes and determined the sources of IFN-gamma during acute T. cruzi infection. We observed that natural killer (NK) cells increased by day 7, while T and B cells increased by day 14. Among CD3+ cells, CD4+, CD8+, and CD4- CD8- cell populations were greatly expanded. A large fraction of CD3+ cells were positive for PanNK, a beta1 integrin expressed by NK and NK T cells. However, these lymphocytes were not classic NK T cells because they did not express NK1.1 and showed no preferential usage of Vbeta8. Otherwise, liver NK T (CD3+ NK1.1+) cells were not increased in acutely infected mice. The majority of PanNK+ CD4+ and PanNK+ CD8+ cells expressed T-cell receptor alphabeta (TCRalphabeta), whereas PanNK+ CD4- CD8- cells were positive for TCRgammadelta. In fact, gammadelta T cells showed the most remarkable increase (40- to 100-fold) among liver lymphocytes. Most importantly, intracellular analysis revealed high levels of IFN-gamma production at day 7 by NK cells and at day 14 by CD4+, CD8+, and CD4- CD8- TCRgammadelta+ cells. We concluded that NK cells are a precocious source of IFN-gamma in the livers of acutely infected mice, and, as the disease progresses, conventional CD4+ and CD8+ T cells and gammadelta T cells, but not classic NK-T cells, may provide the IFN-gamma required for liver protection against T. cruzi.

Pulmonary Mycobacterium intermedium disease in an elderly man with healed pulmonary tuberculosis

A 76-year-old man with a history of pulmonary tuberculosis was found to be sputum smear positive for acid-fast bacilli. The 16S rRNA sequence identified the culture isolate as Mycobacterium intermedium, the pathogenicity of which has not been confirmed. Chemotherapy with isoniazid, rifampin, and ethambutol resulted in clinical improvement.

Impact of genotypic studies on mycobacterial taxonomy: the new mycobacteria of the 1990s

The advancement of genetic techniques has greatly boosted taxonomic studies in recent years. Within the genus Mycobacterium, 42 new species have been detected since 1990, most of which were grown from clinical samples. Along with species for which relatively large numbers of strains have been reported, some of the new species of mycobacteria have been detected rarely or even only once. From the phenotypic point of view, among the new taxa, chromogens exceed nonchromogens while the numbers of slowly and rapidly growing species are equivalent. Whereas conventional identification tests were usually inconclusive, an important role was played by lipid analyses and in particular by high-performance liquid chromatography. Genotypic investigations based on sequencing of 16S rRNA gene have certainly made the most important contribution. The investigation of genetic relatedness led to the redistribution of the species previously included in the classically known categories of slow and rapid growers into new groupings. Within slow growers, the intermediate branch related to Mycobacterium simiae and the cluster of organisms related to Mycobacterium terrae have been differentiated; among rapid growers, the group of thermotolerant mycobacteria has emerged. The majority of species are resistant to isoniazid and, to a lesser extent, to rifampin. Many of the new species of mycobacteria are potentially pathogenic, and there are numerous reports of their involvement in diseases. Apart from disseminated and localized diseases in immunocompromised patients, the most frequent infections in immunocompetent people involve the lungs, skin, and, in children, cervical lymph nodes. The awareness of such new mycobacteria, far from being a merely speculative exercise, is therefore important for clinicians and microbiologists.

The basis of persistent bacterial infections

Selected bacterial pathogens, such as Helicobacter pylori and Mycobacterium tuberculosis, establish persistent infections in mammalian hosts despite activating inflammatory and antimicrobial responses. The strategies used to overcome host defense responses vary with the anatomical location of the infection but often rely on deliberate manipulations of the host cell responses. Phylogenetically unrelated bacteria can share similar strategies for the establishment of persistence and, in selected examples, one even can define homologous "persistence" genes. Such observations suggest that persistent infection is a specific phase in infection pathogenesis rather than a fortuitous imbalance in the host-pathogen interaction.

Non-tuberculous mycobacterial pulmonary infections

Pulmonary disease due to EM occurs worldwide, and its prevalence has increased as a consequence of the HIV pandemic. It is not often detected in the tropics owing to a lack of laboratory facilities, but when sought it has been found. In addition to HIV infection certain occupations such as mining render the work force more susceptible to disease and calls for a revision of working conditions. Resolution by therapy can be achieved in many cases. As the prevalence of TB diminishes worldwide--and hopefully it will in the wake of the resurgence of interest and the widespread application of the World Health Organization's Directly Observed Therapy Short Course (DOTS) strategy--disease due to EM will become relatively more important and will necessitate revised strategies in clinical, microbiological, and public health approaches to mycobacterial disease.

IFN-gamma and NO in mycobacterial disease: new jobs for old hands

Granulomatous disease following exposure to Mycobacterium tuberculosis, Mycobacterium leprae or Mycobacterium avium is correlated with strong inflammatory and protective responses. The mouse model of mycobacterial infection provides an excellent tool with which to examine the inter-relationship between protective cell-mediated immunity and tissue-damaging hypersensitivity. It is well established that T cells and interferon (IFN)-gamma are necessary components of anti-bacterial protection. We propose that IFN-gamma also modulates the local cellular response by downregulating lymphocyte activation and by driving T cells into apoptosis, and that the events that limit excessive inflammation are largely mediated by IFN-gamma-induced nitric oxide (NO). In several murine models of mycobacterial infection, the absence of IFN-gamma and/or NO results in dysregulated granuloma formation and increased lymphocytic responses, which, in the case of M. avium infection, even leads to reduced bacterial growth.

Infection and disease caused by environmental mycobacteria

Many species of mycobacteria that normally live as environmental saprophytes, the environmental mycobacteria (EM), are opportunist causes of disease in humans and animals. Many, but not all, cases are associated with some form of immune deficiency. An increasing number of species and clinical presentations are being described, and advances are being made in the understanding of the underlying predisposing factors. In recent years, four aspects of EM disease have become particularly relevant to human health: (1) the high prevalence of EM disease in patients with AIDS; (2) the emergence of Buruli ulcer, an ulcerative skin disease caused by Mycobacterium ulcerans, as the third most prevalent mycobacterial disease; (3) the effect of infection by EM on the immune responses to BCG vaccination and on the course and outcome of tuberculosis and leprosy; (4) the controversy over the involvement of mycobacteria, notably M. avium subspecies paratuberculosis, in human inflammatory bowel disease. These aspects change the status of EM from mere curiosities to important direct, indirect, and putative causes of serious and increasingly common human disease.