There is a paucity of information on dendritic cell (DC) responses to vaccinia virus (VACV), including the traffic of DCs to the draining lymph node (dLN). In this study, using a mouse model of infection, we studied skin DC migration in response to VACV and compared it with the tuberculosis vaccine Mycobacterium bovis bacille Calmette-Guérin (BCG), another live attenuated vaccine administered via the skin. In stark contrast to BCG, skin DCs did not relocate to the dLN in response to VACV. Infection with UV-inactivated VACV or modified VACV Ankara promoted DC movement to the dLN, indicating that interference with skin DC migration requires replication-competent VACV. This suppressive effect of VACV was capable of mitigating responses to a secondary challenge with BCG in the skin, ablating DC migration, reducing BCG transport, and delaying CD4 + T cell priming in the dLN. Expression of inflammatory mediators associated with BCG-triggered DC migration were absent from virus-injected skin, suggesting that other pathways invoke DC movement in response to replication-deficient VACV. Despite adamant suppression of DC migration, VACV was still detected early in the dLN and primed Ag-specific CD4 + T cells. In summary, VACV blocks skin DC mobilization from the site of infection while retaining the ability to access the dLN to prime CD4 + T cells.

Inoculation of Mycobacterium bovis Bacille Calmette-Guérin (BCG) in the skin mobilizes local dendritic cells (DC) to the draining lymph node (dLN) in a process that remains incompletely understood. In this study, a mouse model of BCG skin infection was used to investigate mechanisms of skin DC migration to dLNs. We found enhanced transcription of cyclooxygenase (COX)-2 and production of COX-derived PGE 2 early after BCG infection in skin. Animals treated with antagonists for COX or the PGE 2 receptors EP2 and EP4 displayed a marked reduction in the entry of skin DCs and BCG to dLNs, uncovering an important contribution of COX-derived PGE 2 in this migration process. In addition, live BCG bacilli were needed to invoke DC migration through this COX-PGE 2 pathway. Having previously shown that IL-1R partially regulates BCG-induced relocation of skin DCs to dLNs, we investigated whether PGE 2 release was under control of IL-1. Interestingly, IL-1R ligands IL-1α/β were not required for early transcription of COX-2 or production of PGE 2 in BCG-infected skin, suggesting that the DC migration-promoting role of PGE 2 is independent of IL-1α/β in our model. In DC adoptive transfer experiments, EP2/EP4, but not IL-1R, was needed on the moving DCs for full-fledged migration, supporting different modes of action for PGE 2 and IL-1α/β. In summary, our data highlight an important role for PGE 2 in guiding DCs to dLNs in an IL-1–independent manner.

18 Despite the success of Vaccinia virus (VACV) against smallpox there remains a paucity of 19 information on Dendritic cell (DC) responses to the virus, especially on the traffic of DCs and 20 VACV to draining LN (dLN). Herein we studied skin DC migration in response to VACV and 21 compared it to the tuberculosis vaccine Mycobacterium bovis Bacille Calmette-Guérin (BCG), 22 another live-attenuated vaccine administered via the skin. In stark contrast to BCG, skin DCs 23 did not relocate to dLN in response to VACV. This happened in spite of virus-induced 24 accumulation of several other innate-immune cell populations in the dLN. UV inactivation of 25 VACV or use of the Modified Vaccinia virus Ankara (MVA) strain promoted DC movement 26 to dLN, indicating that the virus actively interferes with skin DC migration. This active immune 27 suppression by VACV was potent enough to ablate the mobilization of skin DCs in response to 28 BCG, and to reduce the transport of BCG to dLN. Expression of inflammatory mediators 29 associated with BCG-triggered DC migration were absent from virus-injected skin, suggesting 30 that other pathways provoke DC movement in response to replication-deficient VACV. Despite 31 viral suppression of DC migration, VACV was detected in dLN much earlier than BCG, 32 indicating a rapid, alternative route of viral traffic to dLN despite marked blockade of skin DC 33 mobilization from the site of infection. 34 35 Word count: 217 36 37