Interferon mediated control of Legionella infection
Our recent work, and that of others, has shed a great deal of light on the cellular and molecular interactions that contribute to bacterial clearance in the lung during the innate phase of the response. The broad aim of future work is to investigate the molecular mechanisms by which IFN drives clearance of L. pneumophila from the lung and to establish why macrophages support rather than inhibit intracellular bacterial replication in the presence of IFNγ. This work builds on our new data suggesting that MCs are the primary responders to IFNγ production during L. pneumophila infection and that IFNγ drives a bactericidal response by upregulating the expression of guanylate binding proteins (GBP) and immunity-related GTPases (IRGs). In addition, we found that in vivo, L. pneumophila infected alveolar macrophages downregulate the expression of the IFNγ receptor (Ifngr1) rendering them refractory to IFNγ stimulation. In contrast, MCs maintain Ifngr1 expression and are thus bactericidal. We hypothesise that because macrophages play crucial roles in tissue homeostasis, these cells down regulate Ifngr1 expression, and possibly other cytokine receptors, to restrain inflammation and tissue pathology. This inadvertently makes macrophages a protected replicative niche for intracellular bacterial pathogens. In addition, we will investigate how cigarette smoke serves to influences the activities of immune cells in the lung during bacterial infection. Our preliminary data shows that smoking influences the ingress of immune cells into the lung and the ability of cells to kill bacteria and support their replication.
Interplay between myeloid and T cells for anti-bacterial lung immunity
Myeloid cells are instrumental for antigen-specific priming of naive T cells. In addition, inflammasome activation in myeloid cells results in a rapid, innate-like activation of memory T cells. We have recently observed that innate activation of pulmonary T cells results in IFN production and control of bacterial pulmonary infection. In order to clarify the role of myeloid and T cells in the control of pulmonary bacterial infections, we will use the model of Legionella pneumophila, which causes Legionnaire’s disease in humans - a serious and often fatal community-acquired pneumonia. Alveolar macrophages (AM s) and, in humans, epithelial cells are targets for L. pneumophila infection, although the involvement of inflammatory cells is unclear. Inflammasome activation, particularly NLRC4 and NLRP3, IFN and T cells are key components of the early control of L. pneumophila infection. However, the regulation of myeloid cell activation in vivo and the interplay between these cells and memory T cells in conferring protection is not understood. Here we propose to combine the expertise of Garbi on DCs and T cell responses with that of van Driel and Hartland on L. pneumophila infection to define cellular and molecular events between myeloid and innate-like memory T cells that result in protective host responses. Using advanced flow cytometry, confocal imaging and functional cellular assays, we will investigate (i) the infection kinetics in myeloid cells, (ii) how this impacts inflammasome activation in vivo, (iii) how Legionella transcriptionally affects myeloid cells, and (iv) the contribution of innate activation of memory T cells in resolving the infection. These studies will highlight key mechanisms controlling L. pneumophila replication and may contribute towards new therapeutic strategies.