Serodiagnostic potential of Mycobacterium avium MAV2054 and MAV5183 proteins

Effect and Mechanism of Mycobacterium avium MAV-5183 on Apoptosis of Mouse Ana-1 Macrophages

To investigate the effects and mechanisms of Mycobacterium avium MAV-5183 protein on apoptosis in mouse Ana-1 macrophages. A pET-21a-MAV-5183 recombinant plasmid was constructed. The recombinant MAV-5183 protein was cloned, expressed, purified, and identified using an anti-His-tagged antibody. Rabbits were immunized to obtain antiserum, and its potency and immunoreactivity were assessed through WB. Mouse Ana-1 macrophages were incubated with varying concentrations of MAV-5183 protein. Flow cytometry, following ANNEXIN V-FITC/PI double staining, detected apoptosis. Western Blot analysis was conducted to identify apoptosis-related molecules Caspase-9/8/3 and vesicle-related molecules ASC, NLRP3, and Cleaved-casp1. ELISA measured TNF-α and IL-6 levels in the culture supernatant. LDH activity and ROS levels were analyzed separately. RT-qPCR measured mRNA levels of Caspase-9/8/3, ASC, NLRP3, Caspase-1, IL-1β, Bax, MAPK-p38, Bcl-2, TNF-α, and IL-6. MAV-5183 protein was successfully cloned, purified, and identified. In in vitro studies on Ana-1 macrophages, MAV-5183 protein increased the expression of Caspase-9/8/3, ASC, NLRP3 (P < 0.01), induced ROS secretion (P < 0.05), and promoted inflammatory cytokine secretion (TNF-α, IL-6, P < 0.0001); however, it did not significantly affect LDH (P > 0.05). MAV-5183 also induced apoptosis in Ana-1 macrophages (P < 0.05). RT-qPCR results indicated a significant increase in mRNA expression of Caspase-9/8/3, ASC, NLRP3, TNF-α, IL-6, MAPK-p38, and pro-apoptotic factor Bax (P < 0.01), with no significant effect on Bcl-2 and IL-1β mRNA (P > 0.05). The data indicate that MAV-5183 induces macrophage apoptosis through a caspase-dependent pathway and promotes inflammatory cytokine secretion via ROS.

Recombinant Rv1654 protein of Mycobacterium tuberculosis induces mitochondria-mediated apoptosis in macrophage

Mycobacterium tuberculosis contains diverse immunologically active components. This study investigated the biological function of a newly identified component, Rv1654, with the potential to induce apoptosis in macrophages. Recombinant Rv1654 induced macrophage apoptosis in a caspase-9/3-dependent manner through the production of reactive oxygen species (ROS) and interaction with Toll-like receptor 4. In addition, Rv1654 induced the production of tumor necrosis factor-α, interleukin-6, and monocyte chemoattractant protein-1 through the mitogen-activated protein kinase pathway. Furthermore, Rv1654-induced c-Jun N-terminal kinase (JNK) activation was inhibited by the ROS scavenger and Rv1654-induced apoptosis was inhibited by the JNK inhibitor. Moreover, it was found that treatment of macrophages with Rv1654 led to the loss of mitochondrial membrane potential, release of cytochrome c into the cytosol, and translocation of Bax into the mitochondria. Finally, Rv1654-mediated apoptosis was inhibited in macrophages transfected with Bax siRNA. These results suggest that Rv1654 induces macrophage apoptosis through a mitochondrial-dependent pathway and ROS-mediated JNK activation.

Genetic Involvement of Mycobacterium avium Complex in the Regulation and Manipulation of Innate Immune Functions of Host Cells

Mycobacterium avium complex (MAC), a collection of mycobacterial species representing nontuberculous mycobacteria, are characterized as ubiquitous and opportunistic pathogens. The incidence and prevalence of infectious diseases caused by MAC have been emerging globally due to complications in the treatment of MAC-pulmonary disease (PD) in humans and the lack of understating individual differences in genetic traits and pathogenesis of MAC species or subspecies. Despite genetically close one to another, mycobacteria species belonging to the MAC cause diseases to different host range along with a distinct spectrum of disease. In addition, unlike Mycobacterium tuberculosis, the underlying mechanisms for the pathogenesis of MAC infection from environmental sources of infection to their survival strategies within host cells have not been fully elucidated. In this review, we highlight unique genetic and genotypic differences in MAC species and the virulence factors conferring the ability to MAC for the tactics evading innate immune attacks of host cells based on the recent advances in genetic analysis by exemplifying M. avium subsp. hominissuis, a major representative pathogen causing MAC-PD in humans. Further understanding of the genetic link between host and MAC may contribute to enhance host anti-MAC immunity, but also provide novel therapeutic approaches targeting the pangenesis-associated genes of MAC.

AN INTERFERON GAMMA RELEASE ASSAY FOR THE DETECTION OF IMMUNE SENSITIZATION TO MYCOBACTERIUM BOVIS IN AFRICAN WILD DOGS (LYCAON PICTUS)

In South Africa, the largest proportion of the African wild dog (Lycaon pictus) population resides in regions where buffaloes have a high prevalence of Mycobacterium bovis, the causative agent of bovine tuberculosis (bTB). Recent reports of deaths of wild dogs associated with bTB have raised concerns regarding the threat this disease might pose for this species. In order to understand the potential impact of the disease in wild dogs, diagnostic tools are required to identify infected individuals. The interferon gamma (IFN-γ) release assay (IGRA) is commonly used for tuberculosis (TB) screening of humans, cattle, and other species, and the aim of this study was to develop an IGRA for wild dogs to detect immune sensitization. Blood was collected from immobilized wild dogs from the Ann van Dyk Cheetah Centre (AvDCC; n=9) and Kruger National Park (KNP; n=31). Heparinized whole blood was incubated overnight in QuantiFERON^®-TB Gold (QFT) blood collection tubes and with selected mitogens, after which the plasma fraction was harvested. Three canine IFN-γ enzymelinked immunosorbent assays (ELISAs) were compared for detection of wild dog IFN-γ in plasma and the R&D Quantikine canine IFN-γ ELISA was selected for measurement of M. bovis-specific IFN-γ release in plasma samples. An IGRA result was calculated as the concentration in plasma derived from the QFT TB Antigen tubes minus that in the QFT Nil tube. An IGRA cut-off value was calculated using the IGRA results of M. bovis-unexposed individuals from AvDCC. Using this cut-off value, 74% (23/31) of M. bovis-exposed KNP wild dogs were IGRA positive, indicating immune sensitization to TB antigens in these animals. Three M. bovis culture-positive wild dogs from KNP had IFN-γ concentrations between 758 and 1,445 pg/mL, supporting this interpretation. This warrants further investigation into the prevalence of M. bovis infection in the KNP population.

Mycobacterium avium MAV2052 protein induces apoptosis in murine macrophage cells through Toll-like receptor 4

Mycobacterium avium and its sonic extracts induce apoptosis in macrophages. However, little is known about the M. avium components regulating macrophage apoptosis. In this study, using multidimensional fractionation, we identified MAV2052 protein, which induced macrophage apoptosis in M. avium culture filtrates. The recombinant MAV2052 induced macrophage apoptosis in a caspase-dependent manner. The loss of mitochondrial transmembrane potential (ΔΨm), mitochondrial translocation of Bax, and release of cytochrome c from mitochondria were observed in macrophages treated with MAV2052. Further, reactive oxygen species (ROS) production was required for the apoptosis induced by MAV2052. In addition, ROS and mitogen-activated protein kinases were involved in MAV2052-mediated TNF-α and IL-6 production. ROS-mediated activation of apoptosis signal-regulating kinase 1 (ASK1)-JNK pathway was a major signaling pathway for MAV2052-induced apoptosis. Moreover, MAV2052 bound to Toll-like receptor (TLR) 4 molecule and MAV2052-induced ROS production, ΔΨm loss, and apoptosis were all significantly reduced in TLR4(-/-) macrophages. Altogether, our results suggest that MAV2052 induces apoptotic cell death through TLR4 dependent ROS production and JNK pathway in murine macrophages.

Mycobacterium avium MAV2054 protein induces macrophage apoptosis by targeting mitochondria and reduces intracellular bacterial growth

Mycobacterium avium complex induces macrophage apoptosis. However, the M. avium components that inhibit or trigger apoptosis and their regulating mechanisms remain unclear. We recently identified the immunodominant MAV2054 protein by fractionating M. avium culture filtrate protein by multistep chromatography; this protein showed strong immuno-reactivity in M. avium complex pulmonary disease and in patients with tuberculosis. Here, we investigated the biological effects of MAV2054 on murine macrophages. Recombinant MAV2054 induced caspase-dependent macrophage apoptosis. Enhanced reactive oxygen species production and JNK activation were essential for MAV2054-mediated apoptosis and MAV2054-induced interleukin-6, tumour necrosis factor, and monocyte chemoattractant protein-1 production. MAV2054 was targeted to the mitochondrial compartment of macrophages treated with MAV2054 and infected with M. avium. Dissipation of the mitochondrial transmembrane potential (ΔΨ_m) and depletion of cytochrome c also occurred in MAV2054-treated macrophages. Apoptotic response, reactive oxygen species production, and ΔΨ_m collapse were significantly increased in bone marrow-derived macrophages infected with Mycobacterium smegmatis expressing MAV2054, compared to that in M. smegmatis control. Furthermore, MAV2054 expression suppressed intracellular growth of M. smegmatis and increased the survival rate of M. smegmatis-infected mice. Thus, MAV2054 induces apoptosis via a mitochondrial pathway in macrophages, which may be an innate cellular response to limit intracellular M. avium multiplication.

An evaluation of the use of immunoglobulin A antibody response against mycobacterial antigens for the diagnosis of Mycobacterium bovis infection in cattle

Antibody responses are useful indicators of Mycobacterium bovis infection in cattle. Many studies have evaluated the ability of immunoglobulin G (IgG) to serodiagnose bovine tuberculosis (TB). In the current study, immunoglobulin A (IgA) and IgG responses against the MPB70 and MPB83 antigens of M. bovis, the 38 kDa phosphate-binding lipoprotein (PstS1) that is a well-known serodiagnostic M. tuberculosis antigen, and a newly identified protein, termed Rv1483c, were compared in M. bovis-infected and noninfected cattle as well as in field samples. The diagnostic utility of the IgA antibody to MPB70 and MPB83 for bovine TB was superior or comparable to that of the IgG antibody, and the sensitivity of serodiagnosis increased when the results of antigen binding by IgA and IgG were combined. The sensitivities of the IgG and IgA antibodies to the Rv1483c and PstS1 proteins were significantly lower than those to MPB70 and MPB83, and no diagnostic utility for Rv1483c was observed in field samples. Importantly, the IgA antibody reacted strongly to the MPB70 and MPB83 antigens and differentiated cattle with TB from healthy cattle in a multiantigen printed immunoassay. The results of this study support the feasibility of using IgA antibody against the MPB70 and MPB83 antigens to detect bovine TB. In addition, approaches using assays for both IgA and IgG antibodies may increase detection accuracy.

Envelope protein complexes of Mycobacterium avium subsp. paratuberculosis and their antigenicity

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of Johne's disease, a chronic enteric disease of ruminant animals. In the present study, blue native PAGE electrophoresis and 2D SDS-PAGE were used to separate MAP envelope protein complexes, followed by mass spectrometry (MS) to identify individual proteins within the complexes. Identity of individual proteins within complexes was further confirmed by MS upon excision of spots from 2D SDS-PAGE gels. Among the seven putative membrane complexes observed, major membrane protein (MAP2121c), a key MAP antigen involved in invasion of epithelial cells, was found to form a complex with cysteine desulfurase (MAP2120c). Other complexes found included those involved in energy metabolism (succinate dehydrogenase complex) as well as a complex formed by Cfp29, a characterized T cell antigen of Mycobacterium tuberculosis. To determine antigenicity of proteins, Western blot was performed on replicate 2D SDS-PAGE gels with sera from noninfected control cows (n=9) and naturally infected cows in the subclinical (n=10) and clinical (n=13) stages of infection. Clinical animals recognized MAP2121c in greater proportion than subclinical and control cows, whereas cysteine desulfurase recognition was not differentiated by infection status. To further characterize antigenicity, recombinant proteins were expressed for 10 of the proteins identified and evaluated in an interferon-gamma (IFN-γ) release assay as well as immunoblots. This study reveals the presence of protein complexes in the cell envelope of MAP, suggesting protein interactions in the envelope of this pathogen. Furthermore the identification of antigenic proteins with potential as diagnostic targets was characterized.

Highlight on advances in nontuberculous mycobacterial disease in North America

Nontuberculous mycobacteria (NTM) are ubiquitous in the environment and exist as an important cause of pulmonary infections in humans. Pulmonary involvement is the most common disease manifestation of NTM and the incidence of NTM is growing in North America. Susceptibility to NTM infection is incompletely understood; therefore preventative tools are not well defined. Treatment of pulmonary nontuberculous mycobacterial (NTM) infection is difficult and entails multiple antibiotics and an extended treatment course. Also, there is a considerable variation in treatment management that should be considered before initiating treatment. We highlight the new findings in the epidemiology diagnosis and treatment of mycobacterial infections. We debate new advances regarding NTM infection in cystic fibrosis patients and solid organ transplant recipients. Finally, we introduce a new epidemiologic model for NTM disease based on virulence-exposure-host factors.