Resistance to mycobacterial infection: a pattern of early immune responses leads to a better control of pulmonary infection in C57BL/6 compared with BALB/c mice

Establishment of persistent enteric mycobacterial infection following streptomycin pre-treatment

Mycobacterium avium subsp. paratuberculosis (MAP) is the causative agent of paratuberculosis, a chronic gastrointestinal disease affecting ruminants. This disease remains widespread in part due to the limitations of available diagnostics and vaccines. A representative small animal model of disease could act as a valuable tool for studying its pathogenesis and to develop new methods for paratuberculosis control, but current models are lacking. Streptomycin pre-treatment can reduce colonization resistance and has previously been shown to improve enteric infection in a Salmonella model. Here, we investigated whether streptomycin pre-treatment of mice followed by MAP gavage could act as a model of paratuberculosis which mimics the natural route of infection and disease development in ruminants. The infection outcomes of MAP were compared to M. avium subsp. hominissuis (MAH), an environmental mycobacterium, and M. bovis and M. orygis, two tuberculous mycobacteria. Streptomycin pre-treatment was shown to consistently improve bacterial infection post-oral inoculation. This model led to chronic MAP infection of the intestines and mesenteric lymph nodes (MLNs) up to 24-weeks post-gavage, however there was no evidence of inflammation or disease. These infection outcomes were found to be specific to MAP. When the model was applied to a bacterium of lesser virulence MAH, the infection was comparatively transient. Mice infected with bacteria of greater virulence, M. bovis or M. orygis, developed chronic intestinal and MLN infection with pulmonary disease similar to zoonotic TB. Our findings suggest that a streptomycin pre-treatment mouse model could be applied to future studies to improve enteric infection with MAP and to investigate other modifications underlying MAP enteritis.

Listeria-vectored multi-antigenic tuberculosis vaccine protects C57BL/6 and BALB/c mice and guinea pigs against Mycobacterium tuberculosis challenge

Mycobacterium tuberculosis (Mtb) infects one-third of the world's population and is a leading cause of death from a single infectious agent. New TB vaccines are urgently needed to augment immunity conferred by the current modestly protective BCG vaccine. We have developed live attenuated recombinant Listeria monocytogenes (rLm)-vectored TB vaccines expressing five [Mpt64/23.5-EsxH/TB10.4-EsxA/ESAT6-EsxB/CFP10-Ag85B/r30] (rLmMtb5Ag) or nine (additionally EsxN-PPE68-EspA-TB8.4) immunoprotective Mtb antigens (rLmMtb9Ag) and evaluated them for safety, immunogenicity and efficacy as standalone vaccines in two mouse models and an outbred guinea pig model. In immunogenicity studies, rLmMtb5Ag administered subcutaneously induces significantly enhanced antigen-specific CD4+ and CD8+ T-cell responses in C57BL/6 and BALB/c mice, and rLmMtb9Ag induces antigen-specific CD4+ and CD8+ T-cell proliferation in guinea pigs. In efficacy studies, both rLmMtb5Ag and rLmMtb9Ag are safe and protect C57BL/6 and BALB/c mice and guinea pigs against aerosol challenge with highly virulent Mtb. Hence, multi-antigenic rLm vaccines hold promise as new vaccines against TB.

Enhancement of CD4+ T Cell Function as a Strategy for Improving Antibiotic Therapy Efficacy in Tuberculosis: Does It Work?

Tuberculosis (TB), caused by Mycobacterium tuberculosis (Mtb) remains a major public health problem worldwide due in part to the lack of an effective vaccine and to the lengthy course of antibiotic treatment required for successful cure. Combined immuno/chemotherapeutic intervention represents a major strategy for developing more effective therapies against this important pathogen. Because of the major role of CD4⁺ T cells in containing Mtb infection, augmentation of bacterial specific CD4⁺ T cell responses has been considered as an approach in achieving this aim. Here we present new data from our own research aimed at determining whether boosting CD4⁺ T cell responses can promote antibiotic clearance. In these studies, we first characterized the impact of antibiotic treatment of infected mice on Th1 responses to major Mtb antigens and then performed experiments aimed at sustaining CD4⁺ T cell responsiveness during antibiotic treatment. These included IL-12 infusion, immunization with ESAT-6 and Ag85B immunodominant peptides and adoptive transfer of Th1-polarized CD4⁺ T cells specific for ESAT-6 or Ag85B during the initial month of chemotherapy. These approaches failed to enhance antibiotic clearance of Mtb, indicating that boosting Th1 responses to immunogenic Mtb antigens highly expressed by actively dividing bacteria is not an effective strategy to be used in the initial phase of antibiotic treatment, perhaps because replicating organisms are the first to be eliminated by the drugs. These results are discussed in the context of previously published findings addressing this concept along with possible alternate approaches for harnessing Th1 immunity as an adjunct to chemotherapy.

In-vivo expressed Mycobacterium tuberculosis antigens recognised in three mouse strains after infection and BCG vaccination

Novel tuberculosis (TB)-vaccines preferably should (i) boost host immune responses induced by previous BCG vaccination and (ii) be directed against Mycobacterium tuberculosis (Mtb) proteins expressed throughout the Mtb infection-cycle. Human Mtb antigen-discovery screens identified antigens encoded by Mtb-genes highly expressed during in vivo murine infection (IVE-TB antigens). To translate these findings towards animal models, we determined which IVE-TB-antigens are recognised by T-cells following Mtb challenge or BCG vaccination in three different mouse strains. Eleven Mtb-antigens were recognised across TB-resistant and susceptible mice. Confirming previous human data, several Mtb-antigens induced cytokines other than IFN-γ. Pulmonary cells from susceptible C3HeB/FeJ mice produced less TNF-α, agreeing with the TB-susceptibility phenotype. In addition, responses to several antigens were induced by BCG in C3HeB/FeJ mice, offering potential for boosting. Thus, recognition of promising Mtb-antigens identified in humans validates across multiple mouse TB-infection models with widely differing TB-susceptibilities. This offers translational tools to evaluate IVE-TB-antigens as diagnostic and vaccine antigens.

Early Resistance of Non-virulent Mycobacterial Infection in C57BL/6 Mice Is Associated With Rapid Up-Regulation of Antimicrobial Cathelicidin Camp

Early clearance of tuberculosis is the successful eradication of inhaled bacteria before the development of an adaptive immune response. We previously showed, by utilizing a non-virulent mycobacteria infection model, that C57BL/6 mice are more efficient than BALB/c in their control of bacterial growth in the lungs during the first weeks of the infection. Here, we assessed early (within 1–3 days) innate immune events locally in the lungs to identify factors that may contribute to the control of non-virulent mycobacterial burden. We confirmed that C57BL/6 mice are more resistant to infection compared with BALB/c after intranasal inoculation with mycobacterium. Transcriptomic analyses revealed a remarkably silent signature in C57BL/6 mice despite effective control of bacterial growth. In contrast, BALB/c mice up-regulated genes associated with neutrophil and myeloid cell chemotaxis and migration. Flow cytometry analyses corroborated the transcriptomic analyses and demonstrated influx of both neutrophil and myeloid cell populations in BALB/c mice, while these did not increase in C57BL/6 mice. We further detected increased release of TNF-α from BALB/c lung cells but limited release from C57BL/6-derived cells. However, C57BL/6 mice showed a marked early up-regulation of the Camp gene, encoding the cathelicidin CRAMP peptide, post-mycobacterial exposure. CRAMP (LL-37 in human) expression in the lungs was confirmed using immunofluorescence staining. Altogether, these findings show that C57BL/6 mice can clear the mycobacterial infection early and that this early control is associated with high CRAMP expression in the lungs without concomitant influx of immune cells. The role of CRAMP/LL-37 during mycobacterial infection may be relevant for novel protective strategies, and warrants further studies of human cohorts.

PPE38 Protein of Mycobacterium tuberculosis Inhibits Macrophage MHC Class I Expression and Dampens CD8+ T Cell Responses

Suppression of CD8⁺ T cell activation is a critical mechanism used by Mycobacterium tuberculosis (MTB) to escape protective host immune responses. PPE38 belongs to the unique PPE family of MTB and in our previous study, PPE38 protein was speculated to participate in manipulating macrophage MHC class I pathway. To test this hypothesis, the function of mycobacterial PPE38 protein was assessed here using macrophage and mouse infection models. Decreased amount of MHC class I was observed on the surface of macrophages infected with PPE38-expressing mycobacteria. The transcript of genes encoding MHC class I was also inhibited by PPE38. After infection of C57BL/6 mice with Mycobacterium smegmatis expressing PPE38 (Msmeg-PPE38), decreased number of CD8⁺ T cells was found in spleen, liver, and lungs through immunohistochemical analysis, comparing to the control strain harboring empty vector (Msmeg-V). Consistently, flow cytometry assay showed that fewer effector/memory CD8⁺ T cells (CD44^highCD62L^low) were activated in spleen from Msmeg-PPE38 infected mice. Moreover, Msmeg-PPE38 confers a growth advantage over Msmeg-V in C57BL/6 mice, indicating an effect of PPE38 to favor mycobacterial persistence in vivo. Overall, this study shows a unique biological function of PPE38 protein to facilitate mycobacteria to escape host immunity, and provides hints for TB vaccine development.

CD11c(+) CD103(+) cells of Mycobacterium tuberculosis-infected C57BL/6 but not of BALB/c mice induce a high frequency of interferon-γ- or interleukin-17-producing CD4(+) cells

The magnitude of the cellular adaptive immune response is critical for the control of Mycobacterium tuberculosis infection in the chronic phase. In addition, the genetic background is equally important for resistance or susceptibility to tuberculosis. In this study, we addressed whether lung populations of dendritic cells, obtained from genetically different hosts, would play a role in the magnitude and function of CD4(+) populations generated after M. tuberculosis infection. Thirty days post-infection, C57BL/6 mice, which generate a stronger interferon-γ (IFN-γ)-mediated immune response than BALB/c mice, exhibited a higher number and frequency of lung CD11c(+)  CD11b(-)  CD103(+) cells compared with BALB/c mice, which exhibited a high frequency of lung CD11c(+)  CD11b(+)  CD103(-) cells. CD11c(+)  CD11b(-)  CD103(+) cells, purified from lungs of infected C57BL/6 mice, but not from infected BALB/c mice, induced a higher frequency of IFN-γ-producing or interleukin-17 (IL-17)-producing CD4(+) cells. Moreover, CD4(+) cells also arrive at the lung of C57BL/6 mice faster than in BALB/c mice. This pattern of immune response seems to be associated with higher gene expression for CCL4, CCL19, CCL20 and CCR5 in the lungs of infected C57BL/6 mice compared with infected BALB/c mice. The results described here show that the magnitude of IFN-γ-producing or IL-17-producing CD4(+) cells is dependent on CD11c(+)  CD11b(-)  CD103(+) cells, and this pattern of immune response is directly associated with the host genetic background. Therefore, differences in the genetic background contribute to the identification of immunological biomarkers that can be used to design human assays to predict progression of M. tuberculosis infection.

Histamine induces chemotaxis and phagocytosis in murine bone marrow-derived macrophages and RAW 264.7 macrophage-like cells via histamine H4-receptor

OBJECTIVE

Expression and function of histamine H4-receptor, an immunomodulatory receptor involved in inflammatory diseases, on murine macrophages, which are vital for immunity, were investigated.

MATERIALS AND METHODS

The expression pattern of histamine receptors on bone marrow-derived macrophages of BALB/c mice and on RAW 264.7 cells was studied at the mRNA level by reverse transcription polymerase chain reaction. The functional relevance of histamine receptors was investigated by analyzing histamine-induced chemotaxis and phagocytosis in the presence of histamine receptor antagonists mepyramine (histamine H1-receptor), famotidine (histamine H2-receptor), thioperamide (histamine H3/4-receptors) and JNJ7777120 (histamine H4-receptor).

RESULTS

Both bone marrow-derived macrophages and RAW 264.7 cells express mRNA for histamine H1-receptor and histamine H4-receptor. Residual amounts of histamine H2-receptor mRNA are found in bone marrow-derived macrophages only. In both cellular models, histamine induced chemotaxis and phagocytic activity, which was reduced by thioperamide as well as by JNJ 7777120, but not by mepyramine or famotidine.

CONCLUSION

In murine bone marrow-derived macrophages and RAW 264.7 macrophage-like cells histamine H4-receptor mediates chemotaxis and phagocytic activity.