Interferon-alphabeta mediates partial control of early pulmonary Mycobacterium bovis bacillus Calmette-Guérin infection

Demonstrating the utility of the ex vivo murine mycobacterial growth inhibition assay (MGIA) for high-throughput screening of tuberculosis vaccine candidates against multiple Mycobacterium tuberculosis complex strains

Human tuberculosis (TB) is caused by various members of the Mycobacterium tuberculosis (Mtb) complex. Differences in host response to infection have been reported, illustrative of a need to evaluate efficacy of novel vaccine candidates against multiple strains in preclinical studies. We previously showed that the murine lung and spleen direct mycobacterial growth inhibition assay (MGIA) can be used to assess control of ex vivo mycobacterial growth by host cells. The number of mice required for the assay is significantly lower than in vivo studies, facilitating testing of multiple strains and/or the incorporation of other cellular analyses. Here, we provide proof-of-concept that the murine MGIA can be applied to evaluate vaccine-induced protection against multiple Mtb clinical isolates. Using an ancient and modern strain of the Mtb complex, we demonstrate that ex vivo bacillus Calmette-Guérin (BCG)-mediated mycobacterial growth inhibition recapitulates protection observed in the lung and spleen following in vivo infection of mice. Further, we provide the first report of cellular and transcriptional correlates of BCG-induced growth inhibition in the lung MGIA. The ex vivo MGIA represents a promising platform to gain early insight into vaccine performance against a collection of Mtb strains and improve preclinical evaluation of TB vaccine candidates.

Increased Heme Oxygenase 1 Expression upon a Primary Exposure to the Respiratory Syncytial Virus and a Secondary Mycobacterium bovis Infection

The human respiratory syncytial virus (hRSV) is the leading cause of severe lower respiratory tract infections in infants. Because recurrent epidemics based on reinfection occur in children and adults, hRSV has gained interest as a potential primary pathogen favoring secondary opportunistic infections. Several infection models have shown different mechanisms by which hRSV promotes immunopathology to prevent the development of adaptive protective immunity. However, little is known about the long-lasting effects of viral infection on pulmonary immune surveillance mechanisms. As a first approach, here we evaluated whether a primary infection by hRSV, once resolved, dampens the host immune response to a secondary infection with an attenuated strain of Mycobacterium bovis (M. Bovis) strain referred as to Bacillus Calmette-Guerin (BCG). We analyzed leukocyte dynamics and immunomodulatory molecules in the lungs after eleven- and twenty-one-days post-infection with Mycobacterium, using previous hRSV infected mice, by flow cytometry and the expression of critical genes involved in the immune response by real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Among the latter, we analyzed the expression of Heme Oxygenase (HO)-1 in an immunization scheme in mice. Our data suggest that a pre-infection with hRSV has a conditioning effect promoting lung pathology during a subsequent mycobacterial challenge, characterized by increased infiltration of innate immune cells, including interstitial and alveolar macrophages. Our data also suggest that hRSV impairs pulmonary immune responses, promoting secondary mycobacterial colonization and lung survival, which could be associated with an increase in the expression of HO-1. Additionally, BCG is a commonly used vaccine that can be used as a platform for the generation of new recombinant vaccines, such as a recombinant BCG strain expressing the nucleoprotein of hRSV (rBCG-N-hRSV). Therefore, we evaluated if the immunization with rBCG-N-hRSV could modulate the expression of HO-1. We found a differential expression pattern for HO-1, where a higher induction of HO-1 was detected on epithelial cells compared to dendritic cells during late infection times. This is the first study to demonstrate that infection with hRSV produces damage in the lung epithelium, promoting subsequent mycobacterial colonization, characterized by an increase in the neutrophils and alveolar macrophages recruitment. Moreover, we determined that immunization with rBCG-N-hRSV modulates differentially the expression of HO-1 on immune and epithelial cells, which could be involved in the repair of pulmonary tissue.

Impact of STING Inflammatory Signaling during Intracellular Bacterial Infections

The early detection of bacterial pathogens through immune sensors is an essential step in innate immunity. STING (Stimulator of Interferon Genes) has emerged as a key mediator of inflammation in the setting of infection by connecting pathogen cytosolic recognition with immune responses. STING detects bacteria by directly recognizing cyclic dinucleotides or indirectly by bacterial genomic DNA sensing through the cyclic GMP-AMP synthase (cGAS). Upon activation, STING triggers a plethora of powerful signaling pathways, including the production of type I interferons and proinflammatory cytokines. STING activation has also been associated with the induction of endoplasmic reticulum (ER) stress and the associated inflammatory responses. Recent reports indicate that STING-dependent pathways participate in the metabolic reprogramming of macrophages and contribute to the establishment and maintenance of a robust inflammatory profile. The induction of this inflammatory state is typically antimicrobial and related to pathogen clearance. However, depending on the infection, STING-mediated immune responses can be detrimental to the host, facilitating bacterial survival, indicating an intricate balance between immune signaling and inflammation during bacterial infections. In this paper, we review recent insights regarding the role of STING in inducing an inflammatory profile upon intracellular bacterial entry in host cells and discuss the impact of STING signaling on the outcome of infection. Unraveling the STING-mediated inflammatory responses can enable a better understanding of the pathogenesis of certain bacterial diseases and reveal the potential of new antimicrobial therapy.

Pulmonary mucosal immunity mediated through CpG provides adequate protection against pulmonary Mycobacterium tuberculosis infection in the mouse model. A role for type I interferon

Toll-Like Receptor (TLR) 9 stimulation is required for induction of potent immune responses against pathogen invasion. The use of unmethylated CpG as adjuvants in vaccines provides an excellent means of stimulating adaptive immunity. Our data demonstrate that CpG-C provided prolonged immune responses in the mouse model of tuberculosis when formulated with liposomes and the Mycobacterium tuberculosis antigen ESAT-6. A reduction in the mycobacterial burden was best achieved when administered as an intranasal vaccine and was dependent on type I interferon (IFN). There was a significant difference between CpG-C inoculated wild type and IFN-αR1^-/- mice, indicating that type I IFN plays a role in the immune response following CpG-C inoculation. Further analysis showed that early NK cell presence was not an absolute requirement, although elevated IFN-γ levels were detected in the lungs of mice within 48 h. The reduction in mycobacterial burden was MyD88-independent as CpG-C inoculated MyD88^-/- mice showed comparable mycobacterial burdens to wild type mice with no detriment due to the lack of MyD88. Together our data show that pulmonary stimulation of TLR9 bearing antigen presenting cells resulted in the induction of protective immunity against M. tuberculosis infection that was dependent on type I IFN signaling.

Type I interferon induced by TLR2-TLR4-MyD88-TRIF-IRF3 controls Mycobacterium abscessus subsp. abscessus persistence in murine macrophages via nitric oxide

Mycobacterium abscessus (MAB) is an emerging, rapidly growing non-tuberculous Mycobacterium causing therapy-resistant pulmonary disease especially in patients with cystic fibrosis (CF). Smooth and rough colony type MAB can be isolated from infected patients whereby rough colony type MAB are more often associated with severe disease. Disease severity is also associated with an alternated type I interferon (IFN-I) response of the MAB-infected patients. However the relevance of this response for the outcome of MAB infection is still unknown. In this study, we analyzed the IFNβ expression of murine macrophages infected with a MAB rough colony strain (MAB-R) isolated from a patient with progressive CF and compared it to macrophages infected with the MAB smooth colony type reference strain (MAB-S). We found that MAB-R infected macrophages expressed significantly more IFNβ mRNA and protein than MAB-S infected macrophages. Higher IFNβ induction by MAB-R was associated with higher TNF expression and intracellular killing while low IFNβ induction was associated with lower TNF expression and persistence of MAB-S. IFNβ induction was independent of the intracellular cGAS-STING recognition pathway. MAB appeared to be recognized extracellularly and induced IFNβ expression via TLR2-TLR4-MyD88-TRIF-IRF3 dependent pathways. By using macrophages lacking the IFN-I receptor we demonstrate that MAB induced IFN-I response essentially contributed to restricting MAB-R and MAB-S infections by activating macrophage Nos2 expression and nitric oxide production. Thus IFN-I seem to influence the intrinsic ability of macrophages to control MAB infections. As MAB persists over long time periods in susceptible patients, our findings suggest that virulence of MAB strains is promoted by an insufficient IFN-I response of the host.

Type I interferons in tuberculosis: Foe and occasionally friend

Tuberculosis remains one of the leading causes of mortality worldwide, and, despite its clinical significance, there are still significant gaps in our understanding of pathogenic and protective mechanisms triggered by Mycobacterium tuberculosis infection. Type I interferons (IFN) regulate a broad family of genes that either stimulate or inhibit immune function, having both host-protective and detrimental effects, and exhibit well-characterized antiviral activity. Transcriptional studies have uncovered a potential deleterious role for type I IFN in active tuberculosis. Since then, additional studies in human tuberculosis and experimental mouse models of M. tuberculosis infection support the concept that type I IFN promotes both bacterial expansion and disease pathogenesis. More recently, studies in a different setting have suggested a putative protective role for type I IFN. In this study, we discuss the mechanistic and contextual factors that determine the detrimental versus beneficial outcomes of type I IFN induction during M. tuberculosis infection, from human disease to experimental mouse models of tuberculosis.

Impaired IFN-α-mediated signal in dendritic cells differentiates active from latent tuberculosis

Individuals exposed to Mycobacterium tuberculosis (Mtb) may be infected and remain for the entire life in this condition defined as latent tuberculosis infection (LTBI) or develop active tuberculosis (TB). Among the multiple factors governing the outcome of the infection, dendritic cells (DCs) play a major role in dictating antibacterial immunity. However, current knowledge on the role of the diverse components of human DCs in shaping specific T-cell response during Mtb infection is limited. In this study, we performed a comparative evaluation of peripheral blood circulating DC subsets as well as of monocyte-derived Interferon-α DCs (IFN-DCs) from patients with active TB, subjects with LTBI and healthy donors (HD). The proportion of circulating myeloid BDCA3⁺ DCs (mDC2) and plasmacytoid CD123⁺ DCs (pDCs) declined significantly in active TB patients compared to HD, whereas the same subsets displayed a remarkable activation in LTBI subjects. Simultaneously, the differentiation of IFN-DCs from active TB patients resulted profoundly impaired compared to those from LTBI and HD individuals. Importantly, the altered developmental trait of IFN-DCs from active TB patients was associated with down-modulation of IFN-linked genes, marked changes in molecular signaling conveying antigen (Ag) presentation and full inability to induce Ag-specific T cell response. Thus, these data reveal an important role of IFN-α in determining the induction of Mtb-specific immunity.

Type I Interferons in the Pathogenesis of Tuberculosis: Molecular Drivers and Immunological Consequences

Tuberculosis (TB) remains a major global health threat. Urgent needs in the fight against TB include improved and innovative treatment options for drug-sensitive and -resistant TB as well as reliable biological indicators that discriminate active from latent disease and enable monitoring of treatment success or failure. Prominent interferon (IFN) inducible gene signatures in TB patients and animal models of Mycobacterium tuberculosis infection have drawn significant attention to the roles of type I IFNs in the host response to mycobacterial infections. Here, we review recent developments in the understanding of the innate immune pathways that drive type I IFN responses in mycobacteria-infected host cells and the functional consequences for the host defense against M. tuberculosis, with a view that such insights might be exploited for the development of targeted host-directed immunotherapies and development of reliable biomarkers.

cGAS-STING-TBK1-IRF3/7 induced interferon-β contributes to the clearing of non tuberculous mycobacterial infection in mice

Type I interferons (IFN-I), such as IFN-α and IFN-β are important messengers in the host response against bacterial infections. Knowledge about the role of IFN-I in infections by nontuberculous mycobacteria (NTM) is limited. Here we show that macrophages infected with pathogens of the Mycobacterium avium complex produced significantly lower amounts of IFN-β than macrophages infected with the opportunistic pathogen M. smegmatis. To dissect the molecular mechanisms of this phenomenon, we focused on the obligate pathogen Mycobacterium avium ssp paratuberculosis (MAP) and the opportunistic M. smegmatis. Viability of both bacteria was required for induction of IFN-β in macrophages. Both bacteria induced IFN-β via the cGAS-STING-TBK1-IRF3/7-pathway of IFN-β activation. Stronger phosphorylation of TBK1 and higher amounts of extracellular bacterial DNA in the macrophage cytosol were found in M. smegmatis infected macrophages than in MAP infected macrophages. After intraperitoneal infection of mice, a strong Ifnb induction by M. smegmatis correlated with clearance of the bacteria. In contrast, MAP only induced weak Ifnb expression which correlated with bacterial persistence and increased number of granulomas in the liver. In mice lacking the type I interferon receptor we observed improved survival of M. smegmatis while survival of MAP was similar to that in wildtype mice. On the other hand, treatment of MAP infected wildtype mice with the IFN-I inducer poly(I:C) or recombinant IFN-β impaired the survival of MAP. This indicates an essential role of IFN-I in clearing infections by MAP and M. smegmatis. The expression level of IFN-I is decisive for transient versus persistent NTM infection.

Badger macrophages fail to produce nitric oxide, a key anti-mycobacterial effector molecule

The European badger is recognised as a wildlife reservoir for bovine tuberculosis (bTB); the control of which is complex, costly and controversial. Despite the importance of badgers in bTB and the well-documented role for macrophages as anti-mycobacterial effector cells, badger macrophage (bdMφ) responses remain uncharacterised. Here, we demonstrate that bdMφ fail to produce nitric oxide (NO) or upregulate inducible nitric oxide synthase (iNOS) mRNA following Toll-like receptor (TLR) agonist treatment. BdMφ also failed to make NO after stimulation with recombinant badger interferon gamma (bdIFNγ) or a combination of bdIFNγ and lipopolysaccharide. Exposure of bdMφ to TLR agonists and/or bdIFNγ resulted in upregulated cytokine (IL1β, IL6, IL12 and TNFα) mRNA levels indicating that these critical pathways were otherwise intact. Although stimulation with most TLR agonists resulted in strong cytokine mRNA responses, weaker responses were evident after exposure to TLR9 agonists, potentially due to very low expression of TLR9 in bdMφ. Both NO and TLR9 are important elements of innate immunity to mycobacteria, and these features of bdMφ biology would impair their capacity to resist bTB infection. These findings have significant implications for the development of bTB management strategies, and support the use of vaccination to reduce bTB infection in badgers.

Target control of complex networks

Controlling large natural and technological networks is an outstanding challenge. It is typically neither feasible nor necessary to control the entire network, prompting us to explore target control: the efficient control of a preselected subset of nodes. We show that the structural controllability approach used for full control overestimates the minimum number of driver nodes needed for target control. Here we develop an alternate 'k-walk' theory for directed tree networks, and we rigorously prove that one node can control a set of target nodes if the path length to each target node is unique. For more general cases, we develop a greedy algorithm to approximate the minimum set of driver nodes sufficient for target control. We find that degree heterogeneous networks are target controllable with higher efficiency than homogeneous networks and that the structure of many real-world networks are suitable for efficient target control.

Pattern recognition receptors and cytokines in Mycobacterium tuberculosis infection--the double-edged sword?

Tuberculosis, an infectious disease caused by Mycobacterium tuberculosis (Mtb), remains a major cause of human death worldwide. Innate immunity provides host defense against Mtb. Phagocytosis, characterized by recognition of Mtb by macrophages and dendritic cells (DCs), is the first step of the innate immune defense mechanism. The recognition of Mtb is mediated by pattern recognition receptors (PRRs), expressed on innate immune cells, including toll-like receptors (TLRs), complement receptors, nucleotide oligomerization domain like receptors, dendritic cell-specific intercellular adhesion molecule grabbing nonintegrin (DC-SIGN), mannose receptors, CD14 receptors, scavenger receptors, and FCγ receptors. Interaction of mycobacterial ligands with PRRs leads macrophages and DCs to secrete selected cytokines, which in turn induce interferon-γ- (IFNγ-) dominated immunity. IFNγ and other cytokines like tumor necrosis factor-α (TNFα) regulate mycobacterial growth, granuloma formation, and initiation of the adaptive immune response to Mtb and finally provide protection to the host. However, Mtb can evade destruction by antimicrobial defense mechanisms of the innate immune system as some components of the system may promote survival of the bacteria in these cells and facilitate pathogenesis. Thus, although innate immunity components generally play a protective role against Mtb, they may also facilitate Mtb survival. The involvement of selected PRRs and cytokines on these seemingly contradictory roles is discussed.

Disordered Toll-like receptor 2 responses in the pathogenesis of pulmonary sarcoidosis

In this study, we hypothesized that the granulomatous disorder sarcoidosis is not caused by a single pathogen, but rather results from abnormal responses of Toll-like receptors (TLRs) to conserved bacterial elements. Unsorted bronchoalveolar lavage (BAL) cells from patients with suspected pulmonary sarcoidosis and healthy non-smoking control subjects were stimulated with representative ligands of TLR-2 (in both TLR-2/1 and TLR-2/6 heterodimers) and TLR-4. Responses were determined by assessing resulting production of tumour necrosis factor (TNF)-α and interleukin (IL)-6. BAL cells from patients in whom sarcoidosis was confirmed displayed increased cytokine responses to the TLR-2/1 ligand 19-kDa lipoprotein of Mycobacterium tuberculosis (LpqH) and decreased responses to the TLR-2/6 agonist fibroblast stimulating ligand-1 (FSL)-1. Subsequently, we evaluated the impact of TLR-2 gene deletion in a recently described murine model of T helper type 1 (Th1)-associated lung disease induced by heat-killed Propionibacterium acnes. As quantified by blinded scoring of lung pathology, P. acnes-induced granulomatous pulmonary inflammation was markedly attenuated in TLR-2(-/-) mice compared to wild-type C57BL/6 animals. The findings support a potential role for disordered TLR-2 responses in the pathogenesis of pulmonary sarcoidosis.

Interferon alpha treatment of patients with impaired interferon gamma signaling

Patients with deficiency in the interferon gamma receptor (IFN-γR) are unable to respond properly to IFN-γ and develop severe infections with nontuberculous mycobacteria (NTM). IFN-γ and IFN-α are known to signal through STAT1 and activate many downstream effector genes in common. Therefore, we added IFN-α for treatment of patients with disseminated mycobacterial disease in an effort to complement their IFN-γ signaling defect. We treated four patients with IFN-γR deficiency with adjunctive IFN-α therapy in addition to best available antimicrobial therapy, with or without IFN-γ, depending on the defect. During IFN-α treatment, ex vivo induction of IFN target genes was detected. In addition, IFN-α driven gene expression in patients' cells and mycobacteria induced cytokine response were observed in vitro. Clinical responses varied in these patients. IFN-α therapy was associated with either improvement or stabilization of disease. In no case was disease exacerbated. In patients with profoundly impaired IFN-γ signaling who have refractory infections, IFN-α may have adjunctive anti-mycobacterial effects.

Exacerbated type II interferon response drives hypervirulence and toxic shock by an emergent epidemic strain of Streptococcus suis

Streptococcus suis, a major porcine pathogen, can be transmitted to humans and cause severe symptoms. A large human outbreak associated with an unusual streptococcal toxic shock-like syndrome (STSLS) was described in China. Albeit an early burst of proinflammatory cytokines following Chinese S. suis infection was suggested to be responsible for STSLS case severity, the mechanisms involved are still poorly understood. Using a mouse model, the host response to S. suis infection with a North American intermediately pathogenic strain, a European highly pathogenic strain, and the Chinese epidemic strain was investigated by a whole-genome microarray approach. Proinflammatory genes were expressed at higher levels in mice infected with the Chinese strain than those infected with the European strain. The Chinese strain induced a fast and strong gamma interferon (IFN-γ) response by natural killer (NK) cells. In fact, IFN-γ-knockout mice infected with the Chinese strain showed significantly better survival than wild-type mice. Conversely, infection with the less virulent North American strain resulted in an IFN-β-subjugated, low inflammatory response that might be beneficial for the host to clear the infection. Overall, our data suggest that a highly virulent epidemic strain has evolved to massively activate IFN-γ production, mainly by NK cells, leading to a rapid and lethal STSLS.

The effect of combination IFN-alpha-2a with usual antituberculosis chemotherapy in non-responding tuberculosis and diabetes mellitus: a case report and review of the literature

A limited number of publications indicate that certain interferons (IFNs) may have a role in difficult-to-treat tuberculosis. We present a 48-year-old male diabetic patient who was referred to our department with the presumptive diagnosis of multidrug resistant tuberculosis. During the previous 8 months, he had been treated initially with a four-drug regimen (rifampicin, isoniazid, pyrazinamide, and ethambutol), which was later modified by the addition of streptomycin and ciprofloxacin, but his clinical condition had not improved and his sputum smear microscopy had remained positive to acid-fast bacilli. Cultured Mycobacterium tuberculosis from his sputum was sensitive to rifampicin and isoniazid. We administered IFN-alpha-2a at a low dose of 3 million IU intramuscularly weekly, in combination with isoniazid, rifampicin, ethambutol, and pyrazinamide. Two months after initiation of this therapy, sputum smears became negative, and a dramatic improvement in the patient's clinical and radiological findings occurred. During a 4-year follow-up, all consecutive sputum cultures remain negative. This case provides additional confirmation that certain IFNs could, potentially, be useful as therapeutic adjuncts for selected cases of non-responding tuberculosis and, therefore, merit further consideration.

Genome-wide expression profiling identifies type 1 interferon response pathways in active tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis (M.tb), remains the leading cause of mortality from a single infectious agent. Each year around 9 million individuals newly develop active TB disease, and over 2 billion individuals are latently infected with M.tb worldwide, thus being at risk of developing TB reactivation disease later in life. The underlying mechanisms and pathways of protection against TB in humans, as well as the dynamics of the host response to M.tb infection, are incompletely understood. We carried out whole-genome expression profiling on a cohort of TB patients longitudinally sampled along 3 time-points: during active infection, during treatment, and after completion of curative treatment. We identified molecular signatures involving the upregulation of type-1 interferon (α/β) mediated signaling and chronic inflammation during active TB disease in an Indonesian population, in line with results from two recent studies in ethnically and epidemiologically different populations in Europe and South Africa. Expression profiles were captured in neutrophil-depleted blood samples, indicating a major contribution of lymphocytes and myeloid cells. Expression of type-1 interferon (α/β) genes mediated was also upregulated in the lungs of M.tb infected mice and in infected human macrophages. In patients, the regulated gene expression-signature normalized during treatment, including the type-1 interferon mediated signaling and a concurrent opposite regulation of interferon-gamma. Further analysis revealed IL15RA, UBE2L6 and GBP4 as molecules involved in the type-I interferon response in all three experimental models. Our data is highly suggestive that the innate immune type-I interferon signaling cascade could be used as a quantitative tool for monitoring active TB disease, and provide evidence that components of the patient’s blood gene expression signature bear similarities to the pulmonary and macrophage response to mycobacterial infection.

Dynamic roles of type I and type II IFNs in early infection with Mycobacterium tuberculosis

Although the protective role of type II IFN, or IFN-γ, against Mycobacterium tuberculosis has been established, the effects of type I IFNs are still unclear. One potential confounding factor is the overlap of function between the two signaling pathways. We used mice carrying null mutations in the type I IFNR, type II IFNR, or both and compared their immune responses to those of wild-type mice following aerosol infection with M. tuberculosis. We discovered that, in the absence of a response to IFN-γ, type I IFNs play a nonredundant protective role against tuberculosis. Mice unable to respond to both types of IFNs had more severe lung histopathology for similar bacterial loads and died significantly earlier than did mice with impaired IFN-γ signaling alone. We excluded a role for type I IFN in T cell recruitment, which was IFN-γ dependent, whereas both types of IFNs were required for optimal NK cell recruitment to the lungs. Type I IFN had a time-dependent influence on the composition of lung myeloid cell populations, in particular by limiting the abundance of M. tuberculosis-infected recruited macrophages after the onset of adaptive immunity. We confirmed that response to IFN-γ was essential to control intracellular mycobacterial growth, without any additional effect of type I IFN. Together, our results imply a model in which type I IFN limit the number of target cells that M. tuberculosis can infect in the lungs, whereas IFN-γ enhances their ability to restrict bacterial growth.

Mycobacterium tuberculosis and TLR2 agonists inhibit induction of type I IFN and class I MHC antigen cross processing by TLR9

Dendritic cells (DCs) cross process exogenous Ags and present them by class I MHC (MHC-I) molecules to CD8(+) T cells specific for Ags from viruses and bacteria such as Mycobacterium tuberculosis. Unmethylated CpG DNA signals through TLR9 to induce type I IFN (IFN-alpha/beta), which enhances MHC-I Ag cross processing, but lipoproteins that signal through TLR2 do not induce IFN-alpha/beta. In these studies we observed that M. tuberculosis, which expresses agonists of both TLR9 and TLR2, did not induce production of IFN-alpha/beta or cross processing by murine DCs. Furthermore, M. tuberculosis and TLR2 agonists inhibited induction of IFN-alpha/beta and DC cross processing by CpG DNA. Exogenous IFN-alpha/beta effectively enhanced cross processing of M. bovis bacillus Calmette-Guérin expressing OVA, bypassing the inhibition of induction of endogenous IFN-alpha/beta. In addition, inhibition of TLR9-induced cross processing of M. bovis bacillus Calmette-Guérin expressing OVA could be circumvented by pretreating cells with CpG DNA to induce IFN-alpha/beta and MHC-I cross processing before inhibitory mycobacterial TLR2 agonists were present. Inhibition of the response to one TLR by another may affect the ultimate response to pathogens like M. tuberculosis that express agonists of multiple TLRs, including TLR2 and TLR9. This mechanism may contribute to immune evasion and explain why IFN-alpha/beta provides little contribution to host immunity to M. tuberculosis. However, downregulation of certain TLR responses may benefit the host by preventing detrimental excessive inflammation that may occur in the presence of persistent infection.

Mycobacterium bovis BCG decreases MHC-II expression in vivo on murine lung macrophages and dendritic cells during aerosol infection

Mycobacterium tuberculosis and M. bovis BCG infect APCs. In vitro, mycobacteria inhibit IFN-gamma-induced MHC-II expression by macrophages, but the effects of mycobacteria on lung APCs in vivo remain unclear. To assess MHC-II expression on APCs infected in vivo, mice were aerosol-infected with GFP-expressing BCG. At 28 d, approximately 1% of lung APCs were GFP+ by flow cytometry and CFU data. Most GFP+ cells were CD11b(high)/CD11c(neg-mid) lung macrophages (58-68%) or CD11b(high)/CD11c(high) DCs (28-31%). Lung APC MHC-II expression was higher in infected mice than naïve mice. Within infected lungs, however, MHC-II expression was lower in GFP+ cells than GFP- cells for both macrophages and DCs. MHC-II expression was also inhibited on purified lung macrophages and DCs that were infected with BCG in vitro. Thus, lung APCs that harbor mycobacteria in vivo have decreased MHC-II expression relative to uninfected APCs from the same lung, possibly contributing to evasion of T cell responses.

Modulation of pulmonary dendritic cell function during mycobacterial infection

We have previously reported that during mycobacterial infection, naïve CD4(+) T-cell activation is enhanced in the lungs. We investigated the role of chemokine receptor CCR7 and its ligands in the ability of CD11c(+) lung dendritic cells (DCs) to activate naïve CD4(+) T cells during pulmonary infection with Mycobacterium bovis bacillus Calmette-Guérin (BCG). BCG infection resulted in the accumulation and maturation in the lungs of DCs that persisted as the mycobacterial burden declined. Lung DCs from infected mice expressed more major histocompatibility complex class II (MHC-II) than those from uninfected mice. CCR7 expression levels on lung DCs were comparable among uninfected and infected mice. The gene expression of the CCR7 ligand CCL19 progressively increased throughout BCG infection, and its expression was MyD88 dependent. CD11c(+) lung cells from BCG-infected mice activated ovalbumin (OVA)-specific naïve CD4(+) T cells more than CD11c(+) lung cells from uninfected mice. Interestingly, during peak mycobacterial infection, CD11c(hi) MHC(hi) lung DCs had slightly decreased chemotaxis toward the CCR7 ligand CCL21 and less efficiency in activating naive CD4(+) T cells than DCs from mice during late-stage infection, when few bacilli are found in the lung. These findings suggest that during BCG infection, the inflammation and sustained expression of CCL19 result in the recruitment, activation, and retention in the lung of DCs that can activate naïve CD4(+) T cells in situ.

Adjunctive treatment of disseminated Mycobacterium avium complex infection with interferon alpha-2b in a patient with complete interferon-gamma receptor R1 deficiency

We report adjunct treatment of (interferon) IFN-alpha2b (Intron-A) in a patient with complete interferon-gamma receptor R1 (IFNGR1) deficiency suffering from disseminated infection with Mycobacterium avium complex (MAC) resistant to multiple anti-mycobacterial agents. A low dose of IFN-alpha2b (3 x 10(6) units/m(2) three times weekly subcutaneously) successfully attenuated progressive hepatosplenomegaly and abdominal/retroperitoneal/pelvic lymphadenopathy, although the patient continued to be mycobacteremic. This is the first report of a complete IFNGR1 deficiency treated with adjuvant IFN-alpha2b for disseminated MAC infection.

Immunological options for the treatment of tuberculosis: evaluation of novel therapeutic approaches

The emergence of multidrug-resistant tuberculosis strains and the coinfection with HIV, together with advances in immunology, have led to renewed interest regarding ways to exploit the immune responses against Mycobacterium tuberculosis therapeutically. Here we review the fundamentals of tuberculosis therapy in view of the epidemiological and clinical challenges, and explore the experience with immune-based therapies for the treatment of active tuberculosis. These immune-based therapies are discussed here with the aim of assessing their potential use as adjuncts to chemotherapy.

Modulation of naive CD4+ T-cell responses to an airway antigen during pulmonary mycobacterial infection

During pulmonary mycobacterial infection, there is increased trafficking of dendritic cells from the lungs to the draining lymph nodes. We hypothesized that ongoing mycobacterial infection would modulate recruitment and activation of antigen-specific naive CD4+ T cells after airway antigen challenge. BALB/c mice were infected by aerosol with Mycobacterium bovis BCG. At peak bacterial burden in the lungs (4 to 6 weeks postinfection), carboxy-fluorescein diacetate succinimidyl ester-labeled naive ovalbumin-specific DO11.10 T cells were adoptively transferred into infected and uninfected mice. Recipient mice were challenged intranasally with soluble ovalbumin (OVA), and OVA-specific T-cell responses were measured in the lungs, draining mediastinal lymph nodes (MLN), and spleens. OVA challenge resulted in increased activation and proliferation of OVA-specific T cells in the draining MLN of both infected and uninfected mice. However, only BCG-infected mice had prominent OVA-specific T-cell activation, proliferation, and Th1 differentiation in the lungs. BCG infection caused greater distribution of airway OVA to pulmonary dendritic cells and enhanced presentation of OVA peptide by lung CD11c+ cells. Together, these data suggest that an existing pulmonary mycobacterial infection alters the phenotype of lung dendritic cells so that they can activate antigen-specific naive CD4+ T cells in the lungs in response to airway antigen challenge.