Research ArticleT CELLS

Interfacial actin protrusions mechanically enhance killing by cytotoxic T cells

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Science Immunology  22 Mar 2019:
Vol. 4, Issue 33, eaav5445
DOI: 10.1126/sciimmunol.aav5445

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Zooming in on the kiss of death

Cytotoxic T lymphocytes (CTLs) engage and kill antigen-specific target cells by injecting toxic proteins, including perforin and granzyme, via immunological synapses connecting CTLs with target cells. Using micropillars coated with CTL stimulants, Tamzalit et al. studied the role of mechanical force in aiding delivery of toxins via immunological synapses. This in vitro system facilitates the formation of three-dimensional immune synapses that can be visualized and imaged. By studying actin dynamics and lytic granule fusion within these synapses, they found granule fusion to be physically separated from regions of actin depletion. Their studies illustrate the power of in vitro systems in shedding light on microscopic details of CTL-driven killing of target cells.

Abstract

Cytotoxic T lymphocytes (CTLs) kill by forming immunological synapses with target cells and secreting toxic proteases and the pore-forming protein perforin into the intercellular space. Immunological synapses are highly dynamic structures that boost perforin activity by applying mechanical force against the target cell. Here, we used high-resolution imaging and microfabrication to investigate how CTLs exert synaptic forces and coordinate their mechanical output with perforin secretion. Using micropatterned stimulatory substrates that enable synapse growth in three dimensions, we found that perforin release occurs at the base of actin-rich protrusions that extend from central and intermediate locations within the synapse. These protrusions, which depended on the cytoskeletal regulator WASP and the Arp2/3 actin nucleation complex, were required for synaptic force exertion and efficient killing. They also mediated physical deformation of the target cell surface during CTL–target cell interactions. Our results reveal the mechanical basis of cellular cytotoxicity and highlight the functional importance of dynamic, three-dimensional architecture in immune cell-cell interfaces.

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