Dendritic cell migration to draining lymph node and T-cell priming to Bacille Calmette-Guérin

Abstract

Dendritic cells (DCs) are unique antigen presenting cells that bridge innate and adaptive immunity. DCs sense invading microbes, sample antigen and migrate to the draining lymph node (DLN) where they prime T cells to the microbe. In spite of many advances in DC biology, little is known about what happens in the DLN after inoculation of Mycobacterium bovis Bacille Calmette-Guérin (BCG) in the skin. A BCG footpad infection model was used in this thesis to investigate the above caveat. Some of the important points addressed are the subsets of DCs that migrate from skin to DLN in response to BCG and the factors that regulate this migration. We developed 5- and 6-carboxyfluorescein diacetate succinimidyl ester (CFSE)-based assay to track cell migration from the footpad to the DLN. We found EpCAMlow CD11bhigh DCs to be the main migratory skin DC subset to relocate to the DLN in response to BCG in this model. Migratory DCs were found to home to the T-cell area of the LN, and to co-localize with BCG.

DC and BCG entry into DLN is dependent on IL-1R and MyD88-dependent signaling. The requirement for MyD88 in this process is both DC-intrinsic and -extrinsic. The contribution of the IL-1R ligands IL-1α and IL-1β were found to be redundant for the entry of skin DCs and BCG into the DLN. In addition, DC relocation to DLN is dependent on the BCG inoculation dose, but not on viability of the injected bacilli. Antigen-specific CD4+ T cells expansion to BCG is, however, superior when heat-killed BCG is used. Furthermore, the nematode Heligmosomoides polygyrus (bakeri), which establishes a chronic but localized gut infection, was found to reduce BCG-triggered skin DC migration and to mute BCG-specific CD4+ T cell responses in the DLN.

In summary, using a mouse model of BCG infection, this thesis highlights the discovery of a migratory skin DC sub-population that relocates in an MyD88-dependent manner to the DLN in response to BCG and reports on a series of factors that impact on BCG-triggered skin DC migration in this model, including cytokines, BCG viability, BCG dose, and co-infection with a gut nematode.