Age-dependent humoral responses of children to mycobacterial antigens

B-Cells and Antibodies as Contributors to Effector Immune Responses in Tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb), is still a major threat to mankind, urgently requiring improved vaccination and therapeutic strategies to reduce TB-disease burden. Most present vaccination strategies mainly aim to induce cell-mediated immunity (CMI), yet a series of independent studies has shown that B-cells and antibodies (Abs) may contribute significantly to reduce the mycobacterial burden. Although early studies using B-cell knock out animals did not support a major role for B-cells, more recent studies have provided new evidence that B-cells and Abs can contribute significantly to host defense against Mtb. B-cells and Abs exist in many different functional subsets, each equipped with unique functional properties. In this review, we will summarize current evidence on the contribution of B-cells and Abs to immunity toward Mtb, their potential utility as biomarkers, and their functional contribution to Mtb control.

Mycobacterium Avium Prosthetic Hip Infection on Abatacept Presenting as Fever of Unknown Origin

Non-tuberculous mycobacteria (NTM) are well-described pulmonary pathogens in patients with underlying lung disease. Extra-pulmonary infections with NTM are rare. We describe a prosthetic hip infection with Mycobacterium avium complex. Increased immunosuppressing medications and number of total joint replacements are expected to increase the prevalence of NTM infections in the future.

Nontuberculous Mycobacteria in Two Drinking Water Distribution Systems and the Role of Residual Disinfection

Nontuberculous mycobacteria (NTM) are frequently found in chloraminated drinking water distribution systems (DWDSs) due to their chloramine tolerance. NTM were investigated in the water-main biofilms and drinking water of a chloraminated DWDS in the United States (initial chloramine residual = 3.8 ± 0.1 mg L^-1) and a DWDS in Norway with minimal residual disinfectant (0.08 ± 0.01 mg L^-1). Total mycobacteria and Mycobacterium avium complex (MAC) were quantified by qPCR targeting, respectively, atpE genes and the internal transcribed spacer region. Mycobacteria concentrations in drinking water did not differ between the two systems (P = 0.09; up to 6 × 10⁴ copies L^-1) but were higher in the biofilms from the chloraminated DWDS (P = 5 × 10^-9; up to 5 × 10⁶ copies cm^-2). MAC were not detected in either system. Sequencing of mycobacterial hsp65 genes indicated that the chloraminated DWDS lacked diversity and consisted almost exclusively of M. gordonae. In contrast, there were various novel mycobacteria in the no-residual DWDS. Finally, Mycobacterium- and Methylobacterium-like 16S rRNA genes were often detected simultaneously, though without correlation as previously observed. We conclude that, though residual chloramine may increase mycobacterial biomass in a DWDS, it may also decrease mycobacterial diversity.

Nontuberculous lymphadenitis in children: What management strategy?

OBJECTIVES

Nontuberculous mycobacterial (NTM) lymphadenitis is a rare disease of children under 5 years. Its treatment is not standardized, even a "wait-and-see" approach is shown to be effective in the literature. Here, we discuss the diagnostic and therapeutic strategies employed in our departments.

METHODS

Records of pediatric patients treated for NTM cervical lymphadenitis from 2010 to 2015 in our tertiary center were retrospectively reviewed. Patients underwent cervical echotomography and/or CT scan. Every patient but one had microbiological explorations (NTM polymerase chain reaction [PCR] and culture) on fine needle aspiration of pus and/or adenitis biopsy. Differential diagnoses (tuberculosis, cat scratch disease) were excluded with serologies, chest X-Ray, and PCR on adenitis samples. Patients were classified as "proven diagnosis" (NTM detected), "highly probable" (suggestive clinical and anatomopathological aspect) or "possible" infection (suggestive adenitis alone). Treatments, follow-up and adverse events were reviewed.

RESULTS

Thirty-one patients were treated for NTM, median age 2.40 years (Interquartile Range IQR = [1.85-3.16]). Twenty-nine patients (96.77%) had an isolated cervico-facial localization. Median follow-up was 8.00 months (IQR = [4.20-13.43]). We found 17 "proven diagnosis" (58.62%), 5 "highly probable" (17.24%) and 7 "possible" infections (24.14%). "Proven" infections were due to: Mycobacterium avium (n = 12, 66.67%) and M. intracellulare (n = 5, 27.78%). All 29 patients received antibiotics, which were effective for 10 (34.48%, group 1); 10 underwent surgical excision for a poor outcome with antibiotics (34.48%, group 2); spontaneous or surgical drainage occurred in 9 on antibiotics (31.03%, group 3). The median times to resolution for group 1, 2 and 3 were respectively 6.33 months, 6.22 months and 9.53 months. Antibiotics treatment was mostly clarithromycin (n = 27, 93.10%) and/or rifampicin (n = 19, 65.52%); 18 patients (62.07%) received both. Median antibiotics duration was 6.23 months (IQR = [5.17-7.46]), with good compliance (79.31%). The observed adverse effects were 3 (13.04%) isolated transient transaminase elevations, 1 case (4.35%) of minor creatinine elevation, and 1 case (4.35%) of transient diarrhea. Surgical drainage caused 1 transient marginal mandibular nerve palsy, resolutive after 1 month.

CONCLUSION

Antibiotics in NTM adenitis lead to resolution in 7 months, with good tolerance and compliance. The efficacy of "wait-and-see" attitude in the literature make excision surgery a second line treatment.

L. M. C. F, Ottenhoff THM. IgA and IgG against Mycobacterium tuberculosis Rv2031 discriminate between pulmonary tuberculosis patients, Mycobacterium tuberculosis-infected and non-infected individuals

As part of a major project to investigate protective and diagnostic immune markers against tuberculosis (TB), we measured antibody isotype responses to Mycobacterium tuberculosis (Mtb) antigens (LAM, Rv2031, and HBHA) in cohorts of 149 pulmonary tuberculosis patients (PTBP), 148 household contacts (HHCs), and 68 community controls (CCs) in an endemic setting. ELISA was used to measure levels of IgA, IgG, and IgM from sera of cohorts at baseline, and at 6 and 12 months from entry. The results show that there were significant differences in IgA, IgG, and IgM responses to the different antigens and in the three cohorts. At baseline, the level of IgM against RV2031 and LAM did not vary between cohorts, but the levels of IgA and IgG against Rv2031 were significantly higher in PTB patients than HHCs and CCs, followed by HHCs, and the lowest in CCs. In patients, there was a significant variation in antibody responses before and after chemotherapy. The levels of IgA and IgG against HBHA, and IgA against Rv2031 decreased significantly and remained low, while IgA and IgG against LAM increased significantly and remained high following chemotherapy. However, the levels of IgM against Rv2031 and LAM increased at 6 months but decreased again at 12 months. IgM against HBHA did not show any significant variation before and after chemotherapy. Similarly, there were also significant variations in antibody responses in HHCs over time. Our results show that there are significant variations in IgA, IgG and IgM responses to the different antigens and in the three cohorts, implying that not all antibody isotype responses are markers of clinical TB. In addition, the current and previous studies consistently show that IgA and IgG against Rv2031 discriminate between clinical disease, Mtb-infected and non-infected individuals.

Mycobacterium bovis BCG and New Vaccines for the Prevention of Tuberculosis

Tuberculosis infects millions of people worldwide and remains a leading global killer despite widespread neonatal administration of the tuberculosis vaccine, bacillus Calmette-Guérin (BCG). BCG has clear and sustained efficacy, but after 10 years, its efficacy appears to wane, at least in some populations. Fortunately, there are many new tuberculosis vaccines in development today, some in advanced stages of clinical trial testing. Here we review the epidemiological need for tuberculosis vaccination, including evolving standards for administration to at risk individuals in developing countries. We also examine proven sources of immune protection from tuberculosis, which to date have exclusively involved natural or vaccine exposure to whole cell mycobacteria. After summarizing evidence for the use and efficacy of BCG, we detail the most promising new candidate vaccines against tuberculosis. The global need for a new tuberculosis vaccine is acute and huge, but clinical trials to be completed in the coming few years are likely either to identify a new tuberculosis vaccine or to substantially reframe how we understand immune protection from this historical scourge.

Dose response models and a quantitative microbial risk assessment framework for the Mycobacterium avium complex that account for recent developments in molecular biology, taxonomy, and epidemiology

Mycobacterium avium complex (MAC) is a group of environmentally-transmitted pathogens of great public health importance. This group is known to be harbored, amplified, and selected for more human-virulent characteristics by amoeba species in aquatic biofilms. However, a quantitative microbial risk assessment (QMRA) has not been performed due to the lack of dose response models resulting from significant heterogeneity within even a single species or subspecies of MAC, as well as the range of human susceptibilities to mycobacterial disease. The primary human-relevant species and subspecies responsible for the majority of the human disease burden and present in drinking water, biofilms, and soil are M. avium subsp. hominissuis, M. intracellulare, and M. chimaera. A critical review of the published literature identified important health endpoints, exposure routes, and susceptible populations for MAC risk assessment. In addition, data sets for quantitative dose-response functions were extracted from published in vivo animal dosing experiments. As a result, seven new exponential dose response models for human-relevant species of MAC with endpoints of lung lesions, death, disseminated infection, liver infection, and lymph node lesions are proposed. Although current physical and biochemical tests used in clinical settings do not differentiate between M. avium and M. intracellulare, differentiating between environmental species and subspecies of the MAC can aid in the assessment of health risks and control of MAC sources. A framework is proposed for incorporating the proposed dose response models into susceptible population- and exposure route-specific QMRA models.

Isolation of Mycobacterium avium from Potable Water in Homes and Institutions of Patients with HIV Infection in Finland and the United States

Symptomatic disease by nontuberculous mycobacteria has been linked to potable water from institutional and domestic potable water systems. Potable water samples were collected from homes and institutions of patients with AIDS. Colonization of potable water with nontuberculous mycobacteria was demonstrated in 230 (15%) of 1489 samples collected from domestic and institutional water systems of patients with HIV infection in the United States and Finland. Mycobacterium avium was the most common species and colonization was favored at temperatures of 40–50°C in recirculating hot water systems. Such systems are a plausible source of human infection and disease.

Role of B cells and antibodies in acquired immunity against Mycobacterium tuberculosis

Accumulating evidence has documented a role for B cells and antibodies (Abs) in the immunity against Mycobacterium tuberculosis (Mtb). Passive transfer studies with monoclonal antibodies (mAbs) against mycobacterial antigens have shown protection against the tubercle bacillus. B cells and Abs are believed to contribute to an enhanced immune response against Mtb by modulating various immunological components in the infected host including the T-cell compartment. Nevertheless, the extent and contribution of B cells and Abs to protection against Mtb remains uncertain. In this article we summarize the most relevant findings supporting the role of B cells and Abs in the defense against Mtb and discuss the potential mechanisms of protection.

Effects of infection and disease with Mycobacterium tuberculosis on serum antibody to glucan and arabinomannan: two surface polysaccharides of this pathogen

BACKGROUND

The role of the surface capsular polysaccharides (CPs) of Mycobacterium tuberculosis (Mtb) in the pathogenesis of infection and disease, as well their potential for use as diagnostic reagents and vaccine antigens, are unknown.

METHODS

Serum antibody to two CPs of Mtb, arabinomannan (AM) and glucan (Glu), were studied in samples from 52 18-74 year-old HIV-seronegative, immunocompetent individuals in Houston Texas. The effects of Mtb exposure, infection and disease upon the levels of antibodies to these CPs were assessed. Subjects were grouped according to the standard international classification.

RESULTS

IgA anti-Glu levels were significantly higher in the active and treated TB compared to a group that was PPD-negative without TB exposure history (p<0.05). Antibodies against AM demonstrated a similar pattern, with the exception that IgG anti-AM was higher in groups who had active TB or previously documented active TB, and IgA anti-AM was higher in subjects with previously documented active TB compared to the level in an unexposed, PPD-negative group (p<0.05). Serum IgG anti-Glu levels were higher in subjects with active TB or previously documented active TB than in the unexposed PPD-negative group, but the differences were not significant.

CONCLUSIONS

These data suggest that the evaluation of antibody responses to the CP of Mtb may have utility for TB serodiagnosis, and that vaccines designed to induce humoral responses to TB CPs should be tested for their capacity to evoke anti-tuberculosis protective immunity.

Mycobacterium avium subsp. avium and subsp. hominissuis give different cytokine responses after in vitro stimulation of human blood mononuclear cells

Background

Mycobacterium avium is the principal etiologic agent of non-tuberculous lymphadenitis in children. It is also a known pathogen for birds and other animals. Genetic typing of M. avium isolates has led to a proposal to expand the set of subspecies to include M. avium subsp. hominissuis. Isolates associated with disease in humans belong to this subspecies.

Methodology/Principal Findings

Peripheral blood mononuclear cells from six healthy blood donors were stimulated in vitro with ten isolates of M. avium avium and 11 isolates of M. avium hominissuis followed by multiplex bead array quantification of cytokines in supernatants. M. avium hominissuis isolates induced significantly more IL-10 and significantly less IL-12p70, TNF, IFN-γ and IL-17 when compared to M. avium avium isolates. All strains induced high levels of IL-17, but had very low levels of IL-12p70.

Conclusion/Significance

The strong association between M. avium subsp. hominissuis and disease in humans and the clear differences in the human immune response to M. avium subsp. hominissuis compared to M. avium subsp. avium isolates, as demonstrated in this study, suggest that genetic differences between M. avium isolates play an important role in the pathogenicity in humans.

Nontuberculous mycobacteria infections in immunocompromised patients: single institution experience

Disseminated infection due to nontuberculous Mycobacterium (NTM) species is rare in pediatrics. Here we report 6 infections affecting 5 patients at a single institution in an immunocompromised population of pediatric oncology and stem cell transplant recipients. The patients presented within a 1-year period with catheter-associated bacteremia. New pulmonary nodules were noted in 4 of the 5 patients. All of the infections were due to rapidly growing NTM. Patients were successfully treated with removal of the infected catheter and combination antibiotic therapy. There are currently no consensus guidelines for treatment of NTM infections in this population, and a therapeutic approach is presented here.

BCG scar and tuberculin reactivity in children and adults

Bacille Calmette-Guérin (BCG) vaccination generally leads to scar formation and tuberculin skin test (TST) reactivity. This study aimed at analysing these 2 parameters and their correlation in a setting with a low prevalence of tuberculosis. Retrospectively, we analysed 314 children and 390 adults living in Sweden and known from records or individual recall to have undergone BCG vaccination. A BCG scar was present in 161 (51%) of the children and in 340 (87%) of the adults. Among children with a scar, 94 (58%) were TST-positive (>or=6 mm) compared to 23 (15%) of 154 children lacking a visible scar. Among adults with a scar, 258 (76%) were TST- positive compared to 23 (46%) of 50 with no scar. Out of 152 non-vaccinated adults, 142 (94.4%) were TST-negative. When 175 TST-negative health care students were BCG-vaccinated in a prospective part of the study, 174 (99%) were found to develop a scar. In essence, the study showed a positive correlation between scar presence and TST reactivity. Furthermore, BCG vaccination of adults in the present setting resulted in consistent scar formation, while scar prevalence in previously vaccinated children was low.

Specificity and diversity of antibodies to Mycobacterium tuberculosis arabinomannan

Arabinomannan (AM) is a polysaccharide antigen of the mycobacterial capsule. However, it is uncertain whether AM constitutes an immunologically distinct fraction of Mycobacterium tuberculosis. In this study, we analyzed the repertoire and specificity of antibodies to AM by using AM-binding murine monoclonal antibodies (MAbs) and human serum samples. Murine MAbs were found to be diverse in their specificity to AM and cross-reactivity with other arabinose-containing mycobacterial polysaccharides, with MAb 9d8 binding exclusively to AM. Human antibodies to AM were detected in serum samples from patients with pulmonary tuberculosis (TB), as well as in those from healthy, purified protein derivative-negative controls, with significantly higher titers among patients. The binding of human antibodies to AM was inhibited by MAb 9d8 in three patients with TB but not in controls. MAb 5c11, which recognizes other mycobacterial arabinose-containing carbohydrates in addition to AM, inhibited the binding of serum samples from 75% of patients and 76% of controls. Analysis of human antibodies with murine MAbs to human V(H) determinants demonstrated diversity among antibodies to AM with qualitative and quantitative differences compared with antibodies to lipoarabinomannan. In summary, our study suggests that antibodies to AM are diverse and heterogeneous with respect to antigen recognition and V(H) determinant expression, with human serum samples containing different subsets of antibodies to AM with the specificities of AM-binding murine MAbs. One MAb and a subset of human antibodies bind AM specifically, suggesting that this polysaccharide is antigenically distinct and is expressed in human infection.

New vaccines for the prevention of tuberculosis

Mycobacterium bovis, bacille Calmette-Guérin (BCG) is administered widely to newborns throughout the world and has been shown to be effective in preventing childhood tuberculosis but not reactivation pulmonary disease or human immunodeficiency virus-associated tuberculosis. Development of a more effective, better standardized, affordable vaccine with durable activity and fewer side effects is a major priority. Contemporary molecular techniques have identified promising immunodominant antigens and novel immunization strategies. Vaccine development has also been informed by an improved understanding of the role of nontuberculous mycobacteria in the efficacy of BCG and in the prevention of tuberculosis. Vaccines under investigation include attenuated or enhanced whole-cell live, whole-cell inactivated, subunit, DNA, and prime-boost vaccines. Several candidate vaccines have demonstrated activity in animal models that is equal to or superior to that of BCG, and human trials are under way. Because there is no identified surrogate marker for protection, identification of an improved vaccine will require long-term efficacy trials in humans.

Skin test reactivity and cellular immune responses to Mycobacterium avium sensitin in AIDS patients at risk for disseminated M. avium infection

Skin tests and lymphocyte proliferation assays (LPA) were performed with Mycobacterium avium sensitin on patients with AIDS. Among 139 subjects, 13% had positive skin test results and 32% had positive LPA results. The LPA may be a more sensitive indicator of prior M. avium infection in this population.