Chemokines control naive CD8 ⁺ T cell selection of optimal lymph node antigen presenting cells

Naive antiviral CD8 ⁺ T cells are activated in the draining LN (DLN) by dendritic cells (DCs) presenting viral antigens. However, many viruses infect LN macrophages, which participate in initiation of innate immunity and B cell activation. To better understand how and why T cells select infected DCs rather than macrophages, we performed intravital microscopy and ex vivo analyses after infecting mice with vaccinia virus (V V), a large DNA virus that infects both LN macrophages and DCs. Although CD8 ⁺ T cells interact with both infected macrophages and DCs in the LN peripheral interfollicular region (PIR), DCs generate more frequent and stable interactions with T cells. V V infection induces rapid release of CCR5-binding chemokines in the LN, and administration of chemokine-neutralizing antibodies diminishes T cell activation by increasing T cell localization to macrophages in the macrophage-rich region (MRR) at the expense of PIR DCs. Similarly, DC ablation increases both T cell localization to the MRR and the duration of T cell-macrophage contacts, resulting in suboptimal T cell activation. Thus, virusinduced chemokines in DLNs enable antiviral CD8 ⁺ T cells to distinguish DCs from macrophages to optimize T cell priming.