title: Behavior and Properties of Mature Lytic Granules at the Immunological Synapse of Human Cytotoxic T Lymphocytes.
abstract: Killing of virally infected cells or tumor cells by cytotoxic T lymphocytes requires targeting of lytic granules to the junction between the CTL and its target. We used whole-cell patch clamp to measure the cell capacitance at fixed intracellular [Ca2+] to study fusion of lytic granules in human CTLs. Expression of a fluorescently labeled human granzyme B construct allowed identification of lytic granule fusion using total internal reflection fluorescence microscopy. In this way capacitance steps due to lytic granule fusion were identified. Our goal was to determine the size of fusing lytic granules and to describe their behavior at the plasma membrane. On average, 5.02 ± 3.09 (mean ± s.d.) lytic granules were released per CTL. The amplitude of lytic granule fusion events was ~ 3.3 fF consistent with a diameter of about 325 nm. Fusion latency was biphasic with time constants of 15.9 and 106 seconds. The dwell time of fusing lytic granules was exponentially distributed with a mean dwell time of 28.5 seconds. Fusion ended in spite of the continued presence of granules at the immune synapse. The mobility of fusing granules at the membrane was indistinguishable from that of lytic granules which failed to fuse. While dwelling at the plasma membrane lytic granules exhibit mobility consistent with docking interspersed with short periods of greater mobility. The failure of lytic granules to fuse when visible in TIRF at the membrane may indicate that a membrane-confined reaction is rate limiting.
authors: Center for Integrative Physiology and Molecular Medicine (CIPMM), Medical Faculty, Saarland University, 66421, Homburg, Germany.
authors: Min
authors: M
authors: Ming
authors: Center for Integrative Physiology and Molecular Medicine (CIPMM), Medical Faculty, Saarland University, 66421, Homburg, Germany.
authors: Claudia
authors: C
authors: Schirra
authors: Center for Integrative Physiology and Molecular Medicine (CIPMM), Medical Faculty, Saarland University, 66421, Homburg, Germany.
authors: Ute
authors: U
authors: Becherer
authors: Center for Integrative Physiology and Molecular Medicine (CIPMM), Medical Faculty, Saarland University, 66421, Homburg, Germany.
authors: David R
authors: DR
authors: Stevens
authors: Center for Integrative Physiology and Molecular Medicine (CIPMM), Medical Faculty, Saarland University, 66421, Homburg, Germany.
authors: Jens
authors: J
authors: Rettig
mesh_terms: D002118:Calcium / Q000276:immunology / Q000378:metabolism; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D003602:Cytotoxicity, Immunologic; D025802:Electric Capacitance; D018274:Electroporation; D005089:Exocytosis; D015870:Gene Expression; D053804:Granzymes / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D006801:Humans; D054992:Immunological Synapses / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D007700:Kinetics; D008164:Luminescent Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D008561:Membrane Fusion / Q000276:immunology*; D008856:Microscopy, Fluorescence; D061251:Primary Cell Culture; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D013997:Time Factors; D000097573:Red Fluorescent Protein
chemical_list: D002118:Calcium; D053804:Granzymes; D008164:Luminescent Proteins; D011993:Recombinant Fusion Proteins; D000097573:Red Fluorescent Protein