Visualizing dynamic microvillar search and stabilization during ligand detection by T cells

Abstract

During immune surveillance, T cells survey the surface of antigen-presenting cells. In searching for peptide-loaded major histocompatibility complexes (pMHCs), they 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 and quantum dot-enabled synaptic contact mapping microscopy to show that anomalous diffusion and fractal organization of microvilli survey the majority of opposing surfaces within 1 minute. Individual dwell times were long enough to discriminate pMHC half-lives and T cell receptor (TCR) accumulation selectively stabilized microvilli. Stabilization was independent of tyrosine kinase signaling and the actin cytoskeleton, suggesting selection for avid TCR microclusters. This work defines the efficient cellular search process against which ligand detection takes place.

ERM-Dependent Assembly of T Cell Receptor Signaling and Co-stimulatory Molecules on Microvilli prior to Activation

“…We found that at both temperatures L-selectin was concentrated on microvilli, 1,2 while CD45 was distributed uniformly throughout the membrane. 1,4,5 Next, we stained T cells with Alexa-647 labelled anti human TCRαβ antibodies at the two temperatures. At 4°C the structure of microvilli on almost all the T cells was intact, and the TCRαβ molecules localized on them (Fig.…”

Molecular Visualization on the Holodeck

“…Another 3D lightsheet microscopy example involves tracking dozens of T-cell surface protrusions used to interrogate antigen presenting cells 21 . Again, VR is well suited to the task by combining stereo perception and hand-controlled time series playback to manually track paths of individual protrusions, determine their lifetimes, and assess localization of fluorescently labeled T-cell receptors seen in a second channel (Figure 3).…”

ERM-Dependent Assembly of T-Cell Receptor Signaling and Co-stimulatory Molecules on Microvilli Prior to Activation

“…Multiple models that attempt to relate T-cell function with the organization of receptors on the cell surface treat the plasma membrane as a 2-D sheet, rather than a 3-D surface (14-18, 20, 48). Recent studies have begun to unearth the pivotal role of microvilli as sensors involved in the initial stages of the immune response (11,12,27,28). In this work we investigated the properties of microvilli that makes them effective sensors.…”

“…4B) also pointed to a homogeneous distribution of the CD45 molecules all over the membrane. Interestingly, two recent studies also demonstrated a uniform distribution of CD45 on the T-cell membrane (27,45).…”

“…We recently discovered that in human peripheral blood T cells and in effector T lymphocytes differentiated from these lymphocytes, TCRαβ molecules are preferentially localized to microvilli, suggesting a role for these dynamic protrusions in initial T cell recognition of cognate antigenic peptides presented by dendritic cells and other APCs (11). Indeed, Krummel and coworkers demonstrated that microvilli function as sensors that scan the surface of encountered APCs within seconds (27). Sherman and co-workers also observed that microvilli are involved in early T-cell activation (12), and Jun and coworkers demonstrated that upon TCR activation T cells release nanoscale microvilli-related vesicles that interact with APCs and transfer cargo to these cells through a process termed trogocytosis (28).…”