During antigen detection, T-cells survey the surface of antigen-presenting cells (APCs), which may display mainly nonstimulatory peptide-loaded major histocompatibility complexes (pMHCs) and only rare cognate antigen in a process involving close (nanometer-scale) membrane apposition. Thus, T-cell must solve a classic trade-off between speed and sensitivity. It has long been supposed that microvilli on T-cells act as sensory organs to enable search, but their strategy has been unknown. We used lattice light-sheet microscopy and quantum dot-enabled synaptic contact mapping microscopy to show how microvilli on the surface of T-cells search opposing cells and surfaces before and during antigen recognition. We uncovered that microvilli on T-cell surfaces dynamically survey the majority of opposing surfaces within one minute through anomalous diffusion. T-cell receptor (TCR) recognition resulted in selective stabilization of receptor-occupied protrusions, which was independent of tyrosine kinase signaling and the actin cytoskeleton. We revealed that TCRs on activated T-cells were nonuniformly distributed on cell membrane: some TCRs were concentrated on microvilli, while other TCRs formed high-density patches on flatter membrane regions. Many microvilli were TCR-occupied, but a small population of microvilli were found not occupied by TCRs. TCR high-density patches moved relative to microvilli. During T-cell-APC interaction, we observed T-cell microvilli projected deep into 3D pockets formed by veil structures on the surface of dendritic cells (DC), and DC membrane also conformed to accommodate T-cell microvilli, which increased the effective close-contact area between T-cell and APC. Such scanning pattern enabled T-cells to efficiently scan more APC surface in given time. This work defines the efficienT-cellular search process against which ligand detection takes place in T-cells.

Citation Format: En Cai, Kyle Marchuk, Casey Beppler, Matthew Krummel. Microvilli enable efficient T-cell antigen search and ligand detection [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr B148.