Spreading the load: Antigen transfer between migratory and lymph node-resident dendritic cells promotes T-cell priming.

Dendritic cells (DC) are specialized in the processing and presentation of antigen for the activation of lymphocytes. Multiple subsets of DCs exist with distinct functions and roles in the initiation of immune responses. DCs found within tissues acquire antigens or become infected by pathogens and migrate to local draining lymph nodes (LN) where they can directly stimulate T cells. These migratory DCs can also transfer antigens to LN-resident DCs and may indirectly enhance T cell priming. In this issue of the European Journal of Immunology, Gurevich et al. [Eur. J. Immunol. 2017. 47: 1802-1818] elegantly demonstrate the influence of the transfer of antigen from migratory DCs to resident DCs on the dynamics of CD8 T-cell priming in mice. Using both in vitro imaging to visualise antigen dissemination and intravital 2-photon microscopy to track T cell clustering with migratory and resident DCs, antigen-donor DC were found to efficiently distribute antigen to recipient DC. This process, which involved LFA-1, enhanced the recruitment of CD8+ T cells into the response and rescued priming when DCs were impaired in presentation capacity. Together, these findings shed light on the dynamics of the transfer of antigens between DCs in vivo for the efficient priming of cytotoxic T cell responses.