Dissecting the molecular mechanisms underpinning T cell help for DC
Dendritic cells (DC) often require stimulation from CD4+ T cells to propagate CD8+ T cell responses, but precisely how T cell help is delivered in vivo and how the interaction between CD40L and CD40 optimises the priming capacity of DC remains unclear. Building on previous findings showing that CD8+ T cell priming upon HSV-1 skin infection depended on DC receiving stimulation from both IFN-a/b and CD4+ T cells to provide IL-15, this project is designed to examine the molecular basis of how T cell help increases the priming capacity of DC. Using an in vitro system, we have observed several differential patterns of how DC respond to innate stimulation and T cell help. Interestingly, while innate stimuli, such as IFN-a/b, required at least 2-3h to induce cytokine and chemokine responses in the DC, amplification of these responses through CD40 ligation required less than 1h of CD40 stimulation, most likely even less. Ongoing work seeks to delineate the underlying molecular mechanisms and identify appropriate markers through which the provision of T cell help to DC can be resolved at the spatiotemporal level in vivo. This project will increase our understanding of the central aspect of DC-T cell interactions leveraging the molecular expertise in Bonn and the in vivo models available in Melbourne.
Role of XCL1 on DC migration in acute viral infections
The adaptive immune system consists of T and B cells that specifically react against a diverse set of pathogens. Before naïve T lymphocytes can differentiate into an efficient force that protects the host from microbial attacks, they require instruction by dendritic cells (DC). DC not only process and present foreign antigens via MHC molecules to allow for the activation of specific T lymphocytes, but also integrate inflammatory cues and microbial signals induced by the invading pathogens into this process. Recent data indicates that chemokines optimize T-cell/DC encounters and shape the differentiation of cytotoxic CD8+ T cells. One chemokine receptor, XCR1, is exclusively expressed by a subset of DC that induce antiviral immunity. Its only ligand is XCL1, which is produced by activated NK cells, Th-1 and CD8+ T cells. In vitro, DC show chemotactic activity towards XCL1, supporting the notion that XCL1 acts as a chemokine. However, the in vivo function of the XCL1-XCR1 axis is largely unknown. In this project, we aim to elucidate the factors that induce XCL1 and how XCL1 regulates the positioning and migration of XCR1 expressing DC in vivo in the steady state and after viral and bacterial infections. We will also investigate the role of another chemokine receptor, CXCR3 that is exclusively expressed on XCR1 DC. Using advanced flow-cytometry, extensive functional analyses, intravital microscopy and histocytometry based on multicolour confocal images from tissue sections, this project will provide novel insights into the role of XCR1 and CXCR3 in immunity. Such detailed analyses will have direct relevance for vaccine design and anti-tumour immunotherapy.