Abstract

T cells are the drivers of adaptive immunity and detect antigens with unprecedented sensitivity and selectivity. To understand this process, studying the very first interactions of a T cell with an antigen presenting cell (APC) will be key. In order to detect an antigen, T cells need to establish a close contact with a target cell that allows its T-cell receptor to bind the presented antigen. We established a complex “second generation” supported lipid bilayer (SLB) model of the APC cell membrane to study the influence of adhesion on microvillar contact formation and antigen detection. We demonstrated a fine balance between adhesion and the cellular glycocalyx governs T cell activation: Removal of adhesion proteins in the SLB reduced T-cell signaling, whereas the glycocalyx was necessary to prevent T-cell over-reactivity. To study T-cell-SLB interactions in more detail we developed an imaging and analysis pipeline to quantitatively characterize close contact formation with high spatial and temporal resolution using TIRF microscopy. We characterised four stages of interaction, and the role of adhesion proteins, as well as membrane topography, throughout them. Our study highlights the importance of adhesion in regulating T-cell function and we could directly visualize the sequence of events underpinning initial T-cell/target contact. Our findings will be important for better understanding immune diseases and developing immune therapies. Cancer cells, for example, can overexpress glycocalyx proteins to prevent an immune response and recently the downregulation of the adhesion protein CD58 has been identified as a route of immune-evasion by tumors.