Imaging T-cell activation: Topography and features of early T-cell contacts

T cells are the drivers of adaptive immunity and detect antigens with unprecedented sensitivity and selectivity. To understand this process, studying the very first interaction of a T cell with an antigen presenting cell (APC) is key. In order to detect an antigen, a close physical contact with the APC needs to be established. This process heavily relies on the interaction of adhesion proteins. Furthermore, the T-cell surface is dominated by microvilli (MV), which are dynamic membrane protrusions involved in antigen search. Despite the importance of these factors in early T-cell contact formation, their influence on antigen detection is incompletely understood.

To address this, we established a complex “second generation” supported lipid bilayer (SLB) model of the APC cell membrane, including a glycocalyx and key adhesion proteins. To study the T-cell-SLB interaction in more detail we also developed an imaging and analysis pipeline to quantitatively characterize close contact formation with high spatial and temporal resolution using TIRF microscopy. We identified four phases of interaction and characterised the influence of adhesion proteins and membrane topography. Dynamic, size constrained MV contacts dominated all stages.

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.