CXCL10+ peripheral activation niches couple preferred sites of Th1 entry with optimal APC encounter

Correct positioning of T cells within infected tissues is critical for T cell activation and pathogen control. Upon tissue entry, effector T cells must efficiently locate antigen-presenting cells (APC) for peripheral activation. We reveal that tissue entry and initial peripheral activation of Th1 effector T cells are tightly linked to perivascular positioning of chemokine-expressing APCs. Dermal inflammation induces tissue-wide de novo generation of discrete perivascular CXCL10(+) cell clusters, enriched for CD11c(+)MHC-II+ monocyte-derived dendritic cells. These chemokine clusters are hotspots'' for both Th1 extravasation and activation in the inflamed skin. CXCR3-dependent Th1 localization to the cluster micro-environment prolongs T-APC interactions and boosts function. Both the frequency and range of these clusters are enhanced via a T helper 1 (Th1)-intrinsic, interferon-gamma (IFN gamma)-dependent positive-feedback loop. Thus, the perivascular CXCL10(+) clusters act as initial peripheral activation niches, optimizing controlled activation broadly throughout the tissue by coupling Th1 tissue entry with enhanced opportunities for Th1-APC encounter.

Automated summary

Perivascular CXCL10(+) clusters act as hotspots for Th1 extravasation and activation in inflamed skin. These chemokine clusters enhance T-APC interactions, prolonging the interaction time and optimizing controlled activation broadly throughout the tissue. Th1-intrinsic, interferon-gamma (IFN gamma)-dependent positive-feedback loop enhances the frequency and range of these clusters.