LAUSR

During immune surveillance, CD8 T cells scan the surface of antigen presenting cells using dynamic microvillar palpation and movements as well as by having their receptors pre-concentrated into patches. Here, we use real-time lattice light sheet microscopy to demonstrate the independence of microvillar and membrane receptor patch scanning. While T cell receptor (TCR) patches can distribute to microvilli, they do so stochastically and not preferentially as for other receptors such as CD62L. The distinctness of TCR patch movement from microvillar movement extends to many other receptors that form patches that also scan independently of the TCR. An exception to this is the CD8 co-receptor which largely co-migrates in patches that overlap with or are closely adjacent to those containing TCRs. Microvilli that assemble into a synapse contain various arrays of the engaged patches, notably of TCRs and the inhibitory receptor PD-1, creating a pastiche of occupancies that vary from microvillar contact to contact. In summary, this work demonstrates that localization of receptor patches within the membrane and on microvillar projections is stochastic prior to antigen detection and that such stochastic variation may play into the generation of many individually-composed receptor patch compositions at a single synapse. Significance statement Motile T cell microvilli palpate surfaces to facilitate surface scanning in a pattern that is independent of the movement of pre-formed patches of transmembrane antigen-receptors across those microvilli; once T cell receptors engage, the microvilli act to scaffold multiple receptors within a microvillar close-contact.