Spatial relationships of microtubule-organizing centers and the contact area of cytotoxic T lymphocytes and target cells.

Abstract

Specific binding (conjugation) of cytotoxic T lymphocytes (CTL) to target cells (TC)is the first step in a multistage process ultimately resulting in dissolution of the TC and recycling of the CTL. We examined the position of the microtubule organizing center (MTOC) of immune CTL bound to specific TC. Immunofluorescence labeling of freshly prepared CTL-TC conjugates with tubulin antibodies indicated that the MTOC in essentially all conjugated CTL but not in the conjugated TC were oriented towards the intercellular contact site. This finding was corroborated by electron microscopy examination of CTL-TC conjugates fixed either immediately after conjugation or during the lytic process. Antibody-induced caps of membrane antigens of CTL such as H-2 and Thy 1, did not show a similar relationship to the MTOC. Incubation of CTL-TC conjugates, 10-15 min at room temperature, resulted in an apparent deterioration of the microtubular system of conjugated CTL. It is proposed that the CTL plasma membrane proximal to the MTOC is particularly active in forming stable intercellular contacts, resulting in CTL-TC conjugation, and that subsequent modulation of the microtubular system of the CTL may be related to the cytolytic response and to detachment of the effector cell.A prominent manifestation of cell-mediated immunity is the lytic interaction of cytotoxic T lymphocytes (CTL) with appropriate target cells (TC). This process is believed to be relevant to virus, tumor, and transplantation immunity (4, 13, 42). The first step in CTL-mediated lysis is the binding of CTL and TC (conjugation) mediated through specific CTL cell surface receptor(s) and TC major histocompatibility complex determinants. Binding is followed by a lethal hit step delivered by the CTL, ultimately leading to lysis. Following lysis of the TC, effector CTL detach and can recycle to start a new lytic interaction (see references 4,7,8,18,19,23, 28 for reviews).Several observations suggest that the CTL are polar from at least a functional point of view. It has been shown that the lethal hit is strictly unidirectional, i.e., it affects only CTLconjugated TC without causing damage to the effector CTL (40). This "immunity" of the CTL cannot be attributed to an inherent resistance towards the cytolytic process, since CTL of a given type can be readily killed by other specifically immunized CTL (14,17). Moreover, it has been observed that although an individual CTL can bind a number of TC simultaneously, lysis of individual TC occurs sequentially (40, 41). These and other (17) results suggest that the lethal hit, whatever its nature, is expressed in a polar, unidirectional fashion.In this study we examine the possibility that the unidirectional killing activity of CTL is related, at least in part, to a specific polar arrangement of the cytoskeletal system of either the CTL or the TC. We present evidence suggesting polarity by showing that CTL bind predominantly through a cell surface region proximal to the microtubule organizing center (MTOC). Moreover, we de...

The Interaction of Activated Integrin Lymphocyte Function-associated Antigen 1 with Ligand Intercellular Adhesion Molecule 1 Induces Activation and Redistribution of Focal Adhesion Kinase and Proline-rich Tyrosine Kinase 2 in T Lymphocytes

“…Polarization of T lymphocytes upon interaction with APCs or during chemokine directed transendothelial migration is a relevant phenomenon that is thought to contribute importantly to the specificity and effectiveness of immune responses (Geiger et al, 1982;del Pozo et al, 1996;Sánchez-Madrid and del Pozo, 1999). Cell polarization involves the conversion from a spherical to an elongated morphology, a process in which important changes in the organization of the cytoskeleton take place.…”

Les liaisons dangereuses: immunological synapse formation in animals and plants

“…The segregation process of distinct SMACs (called central and peripheral SMACs) requires both TCR ligation and co-stimulation [36,37], is energy-dependent and involves mass transport of randomly distributed lipid raft-like microdomains on the T-cell surface to APC contact sites through cytoskeletal linkage and molecular motors ( Figure 1e) [35,37,38]. Formation of SMACs and maturation of the nascent synapse seems to be driven by cytoskeletal polarization, which is accompanied by the movement of the microtubule-organizing center (MTOC) and Golgi apparatus (GA) beneath contact sites, thereby enabling directed release of cytotoxic granules and cytokines as well as localized TCR internalization [39][40][41]. Numerous TCR proximal signaling molecules are needed for actin accumulation and F-actin dynamics at the immunological synapse [34,41].…”

Mechanisms of granule-dependent killing

“…14 The major granule components are perforin and granzymes, which, upon delivery to the target, combine to engineer rapid cell death with killing time as short as 20 min. 15 Recognition of a target by a CTL cell triggers rapid polarization of the microtubule organizing center (MTOC) toward the immunological synapse, [16][17][18] with granules moving swiftly along microtubules in the direction of the plasma membrane. 19 Both albinism and immune deficiencies are symptomatic of a number of genetic disorders associated with the dysfunction of CTLs and melanocytes, both of which contain secretory lysosomes.…”