Mycobacterium tuberculosis Rv1419 encodes a secreted 13 kDa lectin with immunological reactivity during human tuberculosis

Identification of New Mycobacterium bovis antigens and development of a multiplexed serological bead-immunoassay for the diagnosis of bovine tuberculosis in cattle

Serological assays for bovine tuberculosis diagnosis require the use of multiple Mycobacterium bovis specific antigens to ensure the detection of infected animals. In the present study, identification and selection process of antigens, based on data from published proteomic studies and involving the use of bioinformatics tools and an immuno-screening step, was firstly performed for identifying novel antigens that elicit an antibody response in M. bovis infection. Based on this approach, a panel of 10 M. bovis antigens [with known relevance (MPB70, MPB83, MPB70/83, and ESAT6/CFP10) and novel (Mb1961c, Mb1301c, Mb3871, Mb1403, Mb0592, and PE25/PPE41)] were constructed and thenused to develop a new multiplexed serological assay based on Luminex technology. The performance of the Luminex-bTB immunoassay was evaluated using sera from cattle with known tuberculosis status. Among the proteins whose ability to detect bovine tuberculosis was evaluated for the first time, PE25/PPE41 and Mb1403, but not Mb3871, showed good detection capacity. Following multiple antigen combination, the final Luminex-bTB immunoassay included seven antigens (MPB70, MPB83, MPB70/83, ESAT6/CFP10, PE25/PPE41, Mb1403, and Mb0592) and showed better global performance than the immunoassay using the four usual antigens (MPB70, MPB70/83, MPB83 and ESAT6/CFP10). The specificity and sensitivity values were, respectively, of 97.6% and 42.8% when the cut-off of two-positive antigens was used to classify samples as positive. With the use of the more-restrictive criterion of three-positive antigens, the specificity increased to 99.2% but the sensitivity decreased to 23.9%. The analysis of antigen profiles generated with the Luminex-bTB immunoassay showed that mainly serodominant proteins were recognized in samples from infected cattle. The detection of Mb1961c and Mb1301c appeared to be associated with presumed false-positive results. Moreover, sera from cattle originating from bTB-outbreaks but having inconclusive or negative skin test results were identified as positive by the Luminex-bTB immunoassay and showed an antigen pattern associated with M. bovis infection. The Luminex-bTB immunoassay including seven antigens may be useful as adjunct test for the detection of M. bovis-infected herds, and different cut-offs could be applied according to the bovine tuberculosis epidemiological context.

Pan-genome association study of Mycobacterium tuberculosis lineage-4 revealed specific genes related to the high and low prevalence of the disease in patients from the North-Eastern area of Medellín, Colombia

Mycobacterium tuberculosis (Mtb) lineage 4 is responsible for the highest burden of tuberculosis (TB) worldwide. This lineage has been the most prevalent lineage in Colombia, especially in the North-Eastern (NE) area of Medellin, where it has been shown to have a high prevalence of LAM9 SIT42 and Haarlem1 SIT62 sublineages. There is evidence that regardless of environmental factors and host genetics, differences among sublineages of Mtb strains play an important role in the course of infection and disease. Nevertheless, the genetic basis of the success of a sublineage in a specific geographic area remains uncertain. We used a pan-genome-wide association study (pan-GWAS) of 47 Mtb strains isolated from NE Medellin between 2005 and 2008 to identify the genes responsible for the phenotypic differences among high and low prevalence sublineages. Our results allowed the identification of 12 variants in 11 genes, of which 4 genes showed the strongest association to low prevalence (mmpL12, PPE29, Rv1419, and Rv1762c). The first three have been described as necessary for invasion and intracellular survival. Polymorphisms identified in low prevalence isolates may suggest related to a fitness cost of Mtb, which might reflect a decrease in their capacity to be transmitted or to cause an active infection. These results contribute to understanding the success of some sublineages of lineage-4 in a specific geographical area.

Mycobacterial Adhesion: From Hydrophobic to Receptor-Ligand Interactions

Adhesion is crucial for the infective lifestyles of bacterial pathogens. Adhesion to non-living surfaces, other microbial cells, and components of the biofilm extracellular matrix are crucial for biofilm formation and integrity, plus adherence to host factors constitutes a first step leading to an infection. Adhesion is, therefore, at the core of pathogens’ ability to contaminate, transmit, establish residency within a host, and cause an infection. Several mycobacterial species cause diseases in humans and animals with diverse clinical manifestations. Mycobacterium tuberculosis, which enters through the respiratory tract, first adheres to alveolar macrophages and epithelial cells leading up to transmigration across the alveolar epithelium and containment within granulomas. Later, when dissemination occurs, the bacilli need to adhere to extracellular matrix components to infect extrapulmonary sites. Mycobacteria causing zoonotic infections and emerging nontuberculous mycobacterial pathogens follow divergent routes of infection that probably require adapted adhesion mechanisms. New evidence also points to the occurrence of mycobacterial biofilms during infection, emphasizing a need to better understand the adhesive factors required for their formation. Herein, we review the literature on tuberculous and nontuberculous mycobacterial adhesion to living and non-living surfaces, to themselves, to host cells, and to components of the extracellular matrix.

Mycobacterium bovis BCG infection alters the macrophage N-glycome

Macrophage glycosylation is essential to initiate the host-immune defense but may also be targeted by pathogens to promote infection. Indeed, the alteration of the cell-surface glycosylation status may affect the binding of lectins involved in cell activation and adhesion. Herein, we demonstrate that infection by M. bovis BCG induces the remodeling of the N-glycomes of both human primary blood monocyte-derived macrophages (MDM) and macrophage-cell line THP1. MALDI-MS based N-glycomic analysis established that mycobacterial infection induced increased synthesis of biantennary and multifucosylated complex type N-glycans. In contrast, infection of macrophages by M. bovis BCG did not modify the glycosphingolipids composition of macrophages. Further nano-LC-MSⁿ glycotope-centric analysis of total N-glycans demonstrated that the increased fucosylation was due to an increased expression of the Le^x (Galβ1-4[Fucα1-3]GlcNAc) epitope, also known as stage-specific embryonic antigen-1. Modification of the surface expression of Le^x was further confirmed in both MDM and THP-1 cells by FACS analysis using an α1,3-linked fucose specific lectin. Activation with the mycobacterial lipopeptide Pam3Lp19, an agonist of toll-like receptor 2, did not modify the overall fucosylation pattern, which suggests that the infection process is required to modify surface glycosylation. These results pave the way toward the understanding of infection-triggered cell-surface remodeling of macrophages.

Lectins of Mycobacterium tuberculosis - rarely studied proteins

The importance of bacterial lectins for adhesion, pathogenicity, and biofilm formation is well established for many Gram-positive and Gram-negative bacteria. However, there is very little information available about lectins of the tuberculosis-causing bacterium, Mycobacterium tuberculosis (Mtb). In this paper we review previous studies on the carbohydrate-binding characteristics of mycobacteria and related Mtb proteins, discussing their potential relevance to Mtb infection and pathogenesis.

IL-6 release of Rv0183 antigen-stimulated whole blood is a potential biomarker for active tuberculosis patients

OBJECTIVE

New tests for diagnosing active tuberculosis (aTB) are urgently needed, and TB antigen-specific cell-mediated immunity can be expected to develop new testing methods of aTB.

MATERIALS AND METHODS

Rv0183 protein, the only monoglyceride lipase identified in mycobacteria, was used to stimulate freshly heparin-treated whole blood. The Rv0183-specific cytokines/chemokines response associated with aTB was screened firstly with 4 aTB patients and 4 LTBIs, and further evaluated in 192 suspected aTB patients and 372 healthy individuals.

RESULTS

Out of 71 cytokines/chemokines, the response of IL-6 against Rv0183 protein was found to be associated with aTB. The Rv0183-specific IL-6 response was significantly higher in aTB patients (n = 128) than in those with non-TB lung disease (n = 64) and in healthy individuals (n = 327) (p < 0.0001), and not affected by latent TB infection. In IGRA+ suspected active TB patients, the sensitivity, specificity, PPV and NPV of IL-6 response (with cutoff of 235.2 pg/ml) were 85.7%, 100%, 100% and 51.5% for diagnosing aTB, respectively. While in IGRA- ones, they were 87.5%, 80.5%, 60.9% and 95.0% with 174.2 pg/ml IL-6 response as cutoff, respectively.

CONCLUSIONS

These results clearly show that the Rv0183 antigen-specific IL-6 response has the potential to be used as an immune-diagnosis test for active TB in clinical practice.