Parenchymal migration of naive CD4 T cells in lymph nodes (LNs) is mediated by the Rac activator DOCK2 and PI3Kγ and is widely assumed to facilitate efficient screening of dendritic cells (DCs) presenting peptide-MHCs (pMHCs). Yet how CD4 T cell motility, DC density, and pMHC levels interdependently regulate such interactions has not been comprehensively examined. Using intravital imaging of reactive LNs in DC-immunized mice, we show that pMHC levels determined the occurrence and timing of stable CD4 T cell-DC interactions. Despite the variability in interaction parameters, ensuing CD4 T cell proliferation was comparable over a wide range of pMHC levels. Unexpectedly, decreased intrinsic motility of DOCK2 CD4 T cells did not impair encounters with DCs in dense paracortical networks and, instead, increased interaction stability, whereas PI3Kγ deficiency had no effect on interaction parameters. In contrast, intravital and whole-organ imaging showed that DOCK2-driven T cell motility was required to detach from pMHC DCs and to find rare pMHC DCs. In sum, our data uncover flexible signal integration by scanning CD4 T cells, suggesting a search strategy evolved to detect low-frequency DCs presenting high cognate pMHC levels.

Intravital imaging has revealed that T cells change their migratory behavior during physiological activation inside lymphoid tissue. Yet, it remains less well investigated how the intrinsic migratory capacity of activated T cells is regulated by chemokine receptor levels or other regulatory elements. Here, we used an adjuvant-driven inflammation model to examine how motility patterns corresponded with CCR7, CXCR4, and CXCR5 expression levels on ovalbumin-specific DO11.10 CD4+ T cells in draining lymph nodes. We found that while CCR7 and CXCR4 surface levels remained essentially unaltered during the first 48–72 h after activation of CD4+ T cells, their in vitro chemokinetic and directed migratory capacity to the respective ligands, CCL19, CCL21, and CXCL12, was substantially reduced during this time window. Activated T cells recovered from this temporary decrease in motility on day 6 post immunization, coinciding with increased migration to the CXCR5 ligand CXCL13. The transiently impaired CD4+ T cell motility pattern correlated with increased LFA-1 expression and augmented phosphorylation of the microtubule regulator Stathmin on day 3 post immunization, yet neither microtubule destabilization nor integrin blocking could reverse TCR-imprinted unresponsiveness. Furthermore, protein kinase C (PKC) inhibition did not restore chemotactic activity, ruling out PKC-mediated receptor desensitization as mechanism for reduced migration in activated T cells. Thus, we identify a cell-intrinsic, chemokine receptor level-uncoupled decrease in motility in CD4+ T cells shortly after activation, coinciding with clonal expansion. The transiently reduced ability to react to chemokinetic and chemotactic stimuli may contribute to the sequestering of activated CD4+ T cells in reactive peripheral lymph nodes, allowing for integration of costimulatory signals required for full activation.

No abstract