Forschungszentrum Borstel
Forschungszentrum Borstel

Priority Research Area Infections

Microbial Interface Biology


Growth in human macophages

The main focus of the Division of Microbial Interface Biology is the detailed characterization of the interaction between mycobacteria and their target cells, the macrophages.

“To get it, all you have to do is breathe”-  A Tuberculosis infection is in most cases acquired through inhalation of Mycobacterium tuberculosis in aerosolized respiratory secretions from a contagious person coughing, sneezing or talking. The risk of infection is related to the infectiousness of the person with TB, the duration of exposure, the proximity to the source person, the ventilation and the degree of crowding.  In the lung the bacteria get into contact with alveolar macrophages. Whether these cells are capable to kill the bacteria depends on various parameters and processes, which happen at the microbial interface between M. tuberculosis and its host cell, the macrophage. 

Clinical strains of the Mycobacterium tuberculosis complex (MTBC) are genetically more diverse than previously anticipated. We have now identified Clade-specific virulence patterns of clinical isolates of the Mycobacterium tuberculosis Complex in human primary macrophages and aerogenically infected mice. Exclusively human-adapted M. tuberculosis lineages, also termed clade I, comprising “modern” lineages, such as Beijing and Euro-American Haarlem strains, showed a significantly enhanced capability to grow in human macrophages compared to that of clade II strains, which include “ancient” lineages, such as, e.g., East African Indian or M. africanum strains. However, a simple correlation of inflammatory response profiles with strain virulence was not apparent. Our data reveal three different pathogenic profiles: (i) strains of the Beijing lineage are characterized by low uptake, low cytokine induction, and a high replicative potential, (ii) strains of the Haarlem lineage by high uptake, high cytokine induction, and high growth rates, and (iii) EAI strains by low uptake, low cytokine induction, and a low replicative potential. Our findings have significant implications for our understanding of host-pathogen interaction and factors that modulate the outcomes of mycobacterial infections. Future studies addressing the underlying mechanisms and clinical implications need to take into account the diversity of both the pathogen and the host. Reiling N, et al. MBio. Jul 30;4(4). doi:pii: e00250-13 (2013)

Magnetic-labeled mycobacteria

Pathogenic Mycobacterium spp. effectively manipulate the normal progression of their phagosomal compartment and prevent it from fusing with or maturing into an active lysosomal compartment.  To identify structural differences between MTBC phagosomes we established a novel lipid- based, immunomagnetic method  to isolate and functionally characterize M. tuberculosis–containing phagosomes from primary host cells.

Electron microscopic and biochemical analyses of the magnetic phagosome-containing fractions provided evidence of an enhanced presence of bacterial antigens and a differential distribution of proteins involved in the endocytic pathway over time as well as cytokine-dependent changes in the phagosomal protein composition. Due to its relative speed and versatility, the magnetic isolation procedure facilitates the comparative biochemical and mass spectrometric analysis of M. tuberculosis-containing phagosomes (Clade I vs Clade II). This should promote the identification of essential cellular factors and mechanisms, which are needed to successfully eradicate M. tuberculosis by its host cell. In addition, the technique is suitable for the isolation of different pathogen-containing vesicles, thus, it may enable comparative analyses of compartments containing of a broad range of intracellular pathogens in order to identify pathogen-specific novel targets for the treatment of infectious diseases. Steinhäuser C, et al. Traffic.14(3):321-36 (2013).

Expression von Wnt-6 in granulomatösen Läsionen

We also applied systematic gene expression profiling of macrophages infected with mycobacteria to identify novel factors which influence antimicrobial effector mechanisms. We and others have recently identified a “novel” regulatory role for components of the Wnt signaling network to be operative at the interface between innate and adaptive immunity in inflammatory and infectious disease settings including tuberculosis. In essence Wnts can exert both, pro- and anti-inflammatory functions on macrophages and other cells of the immune system.

We now demonstrate that Wnt6 is expressed in granulomatous lesions of M. tuberculosis infected mice and is involved in macrophage differentiation and proliferation. We identified foamy macrophage-like cells as the primary source of Wnt6 in the infected lung and uncovered a TLR-MyD88-NF-kappaB dependent mode of induction in bone marrow derived macrophages. Functional studies in M. tuberculosis-infected macrophages using Wnt6 conditioned medium and Wnt6-deficient macrophages uncovered a Wnt6-dependent induction of macrophage Arginase-1 and the downregulation of TNF-alpha, which points to an unexpected novel role for Wnt6 in macrophage differentiation shifting polarization towards an M2 phenotype. Based on these findings and the observation that the majority of Wnt6 expressing cells contain lipid vesicles as shown by BODIPY staining, it is intriguing to speculate that M. tuberculosis induces Wnt6 to promote the formation of foamy macrophages as a cellular habitat to persist and replicate within the host. Blumenthal, A et al., Blood (2006), Neumann J, et. al. The FASEB Journal  (2010), Schaale K, et al. Eur J Cell Biol.( 2011), Schaale K, et al. Journal of Immunology (2013)

Zytotoxische Wirkung von anti-TB Leitstrukturen auf die Wirtszellen (primäre Makrophagen)

Our macrophages expertise has prompted us to screen the drug efficacy of novel anti-TB compounds in M. tuberculosis-infected primary macrophages. Compounds are first analyzed in a newly developed 96 well based medium throughput system based on GFP-expressing M. tuberculosis (Michelucci A, et al. Proc Natl Acad Sci U S A. (2013)), which allows the screening of small to medium compound libraries for anti-TB activity. In parallel putative cytotoxic effects on primary macrophages are measured online in the same format using the Roche xCelligence system. All three systems have been successfully used and are embedded within the thematic translational transfer unit Tuberculosis (TTU-Tb) within the “Deutsches Zentrum für Infektionsforschung” (DZIF).