Immunological defense mechanisms in tuberculosis and MAC-infection

[Nontuberculous mycobacterial infections]

Nontuberculous mycobacterial (NTM) are found ubiquitously in the environment and are usually of low pathogenicity. Infection occurs via inhalation of aerosols, and some species may cause severe infections. The incidence of NTM infections is rising worldwide. The risk of developing NTM disease depends on the susceptibility of the host as well as the frequency and duration of exposure. In addition to congenital immune deficiencies and immunosuppressive therapy, structural lung and systemic diseases, including rheumatoid arthritis (RA), are associated with an increased risk for NTM infections. The immune response to NTM is complex and relies on the interplay between professional phagocytes and lymphoid cells. This interplay is concerted by three key cytokines: interleukin-12 (IL-12), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ). Targeted immunotherapies, e. g., treatment with TNF inhibitors, interfere with these essential pathways and increase the risk of NTM infection significantly. This review focuses on the relationship between the immune response to NTM and intrinsic and iatrogenic dispositions for NTM infection, with an emphasis on RA.

Levels of soluble delta-like ligand 1 in the serum and cerebrospinal fluid of tuberculous meningitis patients

In this study, the levels of soluble delta-like ligand 1 in cerebrospinal fluid and serum of 50 patients with tuberculous meningitis, 30 patients with viral meningitis, 20 patients with purulent meningitis and 40 subjects without central nervous system disease were determined using an enzyme-linked immunosorbent assay. The mean levels of soluble delta-like ligand 1 in both cerebrospinal fluid and serum from patients with tuberculous meningitis were significantly higher compared with those from patients with viral meningitis or purulent meningitis or from subjects without central nervous system disease. Meanwhile, the level of soluble delta-like ligand 1 gradually decreased as tuberculous meningitis patients recovered. If patients deteriorated after treatment, the level of soluble delta-like ligand 1 in cerebrospinal fluid gradually increased. There was no correlation between the level of soluble delta-like ligand 1 and the protein level/cell number in cerebrospinal fluid. Our findings indicate that the levels of soluble delta-like ligand 1 in cerebrospinal fluid and serum are reliable markers for the diagnosis of tuberculous meningitis and for monitoring treatment progress. At the same time, this index is not influenced by protein levels or cell numbers in cerebrospinal fluid.

Generalized verrucosis in a patient with GATA2 deficiency

Generalized verrucosis is a characteristic of several genetic and immunodeficiency disorders including epidermodysplasia verruciformis; warts, hypogammaglobulinaemia, infections and myelokathexis (WHIM) syndrome; warts, immunodeficiency, lymphoedema and anogenital dysplasia (WILD) syndrome; severe combined immune deficiency and HIV, among others. In recent years, it has been consistently recognized in patients with GATA2 deficiency, a novel immunodeficiency syndrome characterized by monocytopenia, B-cell and natural killer-cell lymphopenia, and a tendency to develop myeloid leukaemias and disseminated mycobacterial, human papillomavirus (HPV) and opportunistic fungal infections. Mutations in GATA2 cause haploinsufficiency and track in families as an autosomal dominant immunodeficiency. GATA2 is a transcription factor involved in early haematopoietic differentiation and lymphatic and vascular development. We describe a case of generalized verrucosis with HPV type 57 presenting in a young man with GATA2 deficiency. GATA2 deficiency is a novel dominant immunodeficiency that is often recognized later in life and should be considered in the differential diagnosis of patients with generalized verrucosis.

Disseminated nontuberculous mycobacterial infection in two children with different immune responses

A diffuse, infiltrating abdominal mass accompanied with fever and anemia in a child raises the possibility of a benign or malignant tumor, pseudotumor, or infection. Herein, we describe a 9-year-old girl and a 14-year-old boy with multiple large abdominal masses, fever, weight loss, and anemia. During the evaluation of the children, the girl was found to be immunocompetent, while the boy was found to be immunocompromised. Computerized tomography of the abdomen in both cases demonstrated multiple large intra-abdominal masses. Tumors in the girl were composed of wide-spread necrotizing granulomas and necrosis with dystrophic calcifications. In the boy, non-necrotic, homogenous histiocytic infiltrates with rare multinucleated giant cells and lymphocytes were observed histologically. Review of histologic sections identified gram-positive, nonbranching acid-fast bacillary organisms in both cases. Diagnoses of Mycobacterium fortuitum (MF) and Mycobacterium avium-intracellulare complex (MAC) were confirmed by tissue microbiologic cultures in the girl and boy, respectively. The girl with MF infection was appropriately treated and is currently doing well. The boy with MAC was found to have human immunodeficiency virus infection/acquired immune deficiency syndrome (AIDS) and is currently undergoing AIDS treatment. These cases highlight the striking contrast between responses to nontuberculous mycobacteria infection based on immune status.

Psoriasis, anti-tumor necrosis factor therapy, and tuberculosis: report of three challenging cases and literature review

INTRODUCTION

The era of biologic therapies has provided new options for the treatment of chronic plaque psoriasis. However, safety concerns have led to intensive screening and monitoring of patients receiving anti-tumor necrosis factor alpha (anti-TNF-alpha) agents.

METHODS

The authors describe the cases of three patients with moderate to severe psoriasis treated with anti-TNF agents, with challenging diagnostic and treatment aspects regarding tuberculosis (TB) infection, a serious adverse event associated with this type of treatment. The cases are discussed in the context of a comprehensive literature review describing the risk of TB associated with the use of TNF inhibitors. A critical review of the clinical trials that have tested the safety of these agents is also presented.

RESULTS

One patient, who tested negatively for latent TB infection (LTBI) during screening, developed active TB under adalimumab therapy. For two other patients the diagnosis and management of LTBI in relation to anti-TNF therapy represented a challenge. Although clinical trials involving the use of anti-TNF therapy for psoriasis haven't demonstrated a high TB incidence, active TB is continuously reported in association with this treatment.

CONCLUSIONS

Findings from clinical practice and the scientific literature indicate that anti-TNF therapies are associated with an increased risk of TB, and close monitoring of patients is needed.

Comparative analysis of immune responses to Mycobacterium abscessus infection and its antigens in two murine models

Mycobacterium abscessus has been identified as an emerging pulmonary pathogen in humans. Because little is known regarding immune responses elicited by M. abscessus or its antigens, immunological responses were studied in two murine models subjected to intravenous (high-dose or systemic infection) or pulmonary (low-dose or local infection) inoculation with M. abscessus ATCC 19977. An overall comparison between the two models showed similar patterns of bacterial survival and host immune responses. The colonization of M. abscessus was the highest at 5 days post-infection (dpi) and its elimination was positively correlated with cell-mediated immunity in both challenges. However, an inverse relationship was observed between progressive inflammation and mycobacterial colonization levels in mice infected with a high dose at 14 dpi. Regarding antigens, culture filtrate (CF) of M. abscessus strongly induced IFN-gamma secretion, whereas cellular extract (CE) antigen elicited strong antibody responses. The antibody response to M. abscessus antigens in mice subjected to low-dose infection increased when the cellular immune response decreased over 14 dpi. However, the antibody response for the high-dose infection increased promptly after the infection. In comparison of cytokine expression in lung homogenates after M. abscessus infection, Thl and Th2 cytokines increased simultaneously in the high-dose infection, whereas only cell-mediated immunity developed in the low-dose pulmonary infection. These findings not only enhance our understanding of the immune response to M. abscessus infection according to systemic or pulmonary infection, but may also aid in immunological diagnosis and vaccine development. M. abscessus, murine infection model, immune response, antigens, cytokines.

Mycobacterium avium complex peritonitis in the setting of cirrhosis: Case report and review of the literature

Mycobacterium avium complex is a rare cause of peritonitis. We report here the fourth case in the literature of MAC peritonitis associated with cirrhosis in the absence of AIDS, and discuss the possibility of different etiologies in persons with and without AIDS.

Mycobacterium paratuberculosisand the bovine immune system

Mycobacterium aviumsubspeciesparatuberculosis(M. paratuberculosis) is the causative agent of Johne’s disease, a deadly intestinal ailment of ruminants. Johne’s disease is of tremendous economic importance to the worldwide dairy industry, causing major losses due to reduced production and early culling of animals. A highly controversial but developing link between exposure toM. paratuberculosisand human Crohn’s disease in some individuals has led to the suggestion thatM. paratuberculosisis also a potential food safety concern. As with many other mycobacteria,M. paratuberculosisis exquisitely adapted to survival in the host, despite aggressive immune reactions to these organisms. One hallmark of mycobacteria, includingM. paratuberculosis, is their propensity to infect macrophages. Inside the macrophage,M. paratuberculosisinterferes with the maturation of the phagosome by an unknown mechanism, thereby evading the host’s normal first line of defense against bacterial pathogens. The host immune system begins a series of attacks againstM. paratuberculosis-infected macrophages, including the rapid deployment of activated γδ T cells, CD4+T cells and cytolytic CD8+T cells. These cells interact with the persistently infected macrophage and with each other through a complex network of cytokines and receptors. Despite these aggressive efforts to clear the infection,M. paratuberculosispersists and the constant struggle of the immune system leads to pronounced damage to the intestinal epithelial cells. Enhancing our ability to control this important and tenacious pathogen will require a deeper understanding of howM. paratuberculosisinterferes with macrophage action, the cell types involved in the immune response, the cytokines these cells use to communicate, and the host genetic factors that control the response to infection.

Disseminated Mycobacterium avium complex infection in an immunocompetent pregnant woman

BACKGROUND

Disseminated mycobacterium avium complex (MAC) occurs mainly in immunocompromised hosts, which is associated with abnormal cellular immunity.

CASE PRESENTATION

A 26-year-old pregnant woman presented with fever and general weakness. Miliary lung nodules were noted on chest X-ray. Under the impression of miliary tuberculosis, anti-tuberculosis medication was administered. However, the patient was not improved. Further work-up demonstrated MAC in the sputum and placenta. The patient was treated successfully with clarithromycin-based combination regimen.

CONCLUSION

This appears to be the first case of disseminated MAC in an otherwise healthy pregnant woman. Clinicians should be alert for the diagnosis of MAC infection in diverse clinical conditions.

Pulmonary infection of Mycobacterium avium-intracellulare complex with simultaneous organizing pneumonia

A 67-year-old woman presented high-grade fever and dyspnea. Sputum culture confirmed Mycobacterium avium-intracellulare complex (MAC). Transbronchial lung biopsies revealed organizing pneumonia (OP) that was rapidly improved with corticosteroid. Five months after onset, a nodule emerged in the right lung. Although MAC was confirmed, the lesion was deemed too small to merit anti-mycobacterial chemotherapy. Four months later, diffuse infiltrates developed on chest X-ray. Bronchoalveolar lavage study identified MAC and exhibited OP patterns. We commenced antimycobacterial chemotherapy. The infiltrates almost completely improved within a month without corticosteroid.

Increased susceptibility of Stat4-deficient and enhanced resistance in Stat6-deficient mice to infection with Trypanosoma cruzi

Although Th1-type responses tend to be associated with resistance to Trypanosoma cruzi infection, mixed Th1 and Th2 cytokine responses are generally observed in both resistant and susceptible mice. To help clarify the role of type 1 and type 2 cytokine responses in immunity to T. cruzi, mice with induced deficiencies in the Stat4 or Stat6 genes were infected with T. cruzi. As expected, Stat4-/- mice deficient in type 1 cytokine responses were highly susceptible to infection, exhibiting increased parasitemia levels relative to wild-type mice and 100% mortality. In contrast, parasitemia levels and survival in Stat6-deficient mice were not different from wild type. The type 1 and type 2 cytokine bias of Stat6- and Stat4-deficient mice, respectively, was confirmed by in situ immunocytochemical analysis of cytokine-producing cells in the tissues of infected mice and by subclass analysis of anti-T. cruzi serum Abs. Notably, both Stat4- and Stat6-deficient mice produced substantial amounts of anti-T. cruzi Abs. Tissues from chronically infected Stat6-deficient mice had little to no evidence of inflammation in the heart and skeletal muscle in contrast to wild-type mice, which exhibited substantial inflammation. In situ PCR analysis of these tissues provided evidence of the persistence of T. cruzi in wild-type mice, but no evidence of parasite persistence in Stat6-deficient mice. These data suggest that type 1 T cells are required for the development of immune control to T. cruzi, but that type 2 T cells contribute to parasite persistence and increased severity of disease.

Nontuberculous Mycobacterial Infections of the Lung

There is an increasing appreciation for the role of nontuberculous mycobacteria (NTM) as pathogens causing pulmonary disease, disseminated disease, or both in immunocompetent and immunocompromised individuals. Species previously considered nonpathogenic have been shown to cause pulmonary infection. The majority of immunocompetent patients with NTM pulmonary infection have underlying lung disease. New diagnostic techniques such as gene probes, gas-liquid and high-pressure chromatography, and polymerase chain reaction offer significant advantages in the rapid identification of NTM species. Some of these techniques allow identification of mycobacteria directly from clinical specimens. The fluoroquinolones, rifabutin, and newer macrolides offer advances in the treatment of infections that are caused by NTM and are resistant to the traditional antimycobacterial drugs.