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Blackwell Munksgaard
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Blackwell Munksgaard 2004
doi: 10.1111/j.1600-0854.2004.00209.x
Review
Retroviral Spread by Induction of Virological Synapses
Clare Jolly* and Quentin J. Sattentau*
The Sir William Dunn School of Pathology, The University
of Oxford, South Parks Road, Oxford OX1 3RE
*Corresponding authors: Quentin J. Sattentau,
Quentin.Sattentau @pathology.ox.ac.uk
Clare Jolly, [email protected]
Cells of the immune system communicate via the formation of receptor-containing adhesive junctions termed
immunological synapses. Recently, retroviruses have
been shown to subvert this process in order to pass
directly from infected to uninfected immune cells. Such
cell–cell viral dissemination appears to function by
triggering existing cellular pathways involved in antigen
presentation and T-cell communication. This mode of
viral spread has important consequences for both the
virus and the host cells in terms of viral pathogenesis
and viral resistance to immune and therapeutic intervention. This review summarises the current knowledge
concerning virological synapses induced by retroviruses.
Key words: adhesion molecules, CD4, CXCR4, HIV-1,
HTLV-1, immunological synapse, viral pathogenesis, viral
receptors, virological synapse
Received 12 May 2004, revised and accepted for publication
26 May 2004
Cell–Cell Contact and Synapses
The ability of cells to interact in a co-ordinated manner is
integral to many biological processes. Communication
often occurs by establishing sites of cell–cell contact that
direct secretion from one cell to another. This type of
cellular teamwork is particularly important in the complex
functioning of the nervous and immune systems
(reviewed in this issue (1)). Cells regulate the distribution
of receptors in the plasma membrane via targeting to
specific microdomains (such as lipid rafts) and/or by
cytoskeleton-driven movement in response to external
stimuli. Some cells, such as epithelial cells, are naturally
polarised, whereas others can be induced to polarise
receptors in response to soluble factors (such as chemokines), transcriptional activation or direct cell–cell contact.
Cells of many different lineages often contact other cell
types during their lifetime. What makes neuronal and
immune cells different is that upon contact, a characteristic arrangement of molecules forms at the cell–cell
junction, which has been termed a synapse. A synapse
has been defined as ‘a stable adhesive junction across
which information is relayed by directed secretion’ (2).
Cell contact promotes outside-in signalling that directs
actin-mediated recruitment of receptors to the interface.
The neurological and immunological synapses (IS) differ in
the receptors that are recruited to the contact site, but
they share a number of similarities that define them as
synapses (2):
the plasma membranes of interacting cells show points
of contiguity but are not continuous and the cells remain
independent and do not fuse;
*
cell–cell recognition is mediated in part by professional
adhesion molecules and the synapse is stable;
*
*
there is directed secretion from one cell towards the other.
Immune Cells and Synapses
The adaptive immune response is dependent on cell
contact to detect and respond effectively to antigenic
challenge. T-lymphocytes are central to this and perform
a variety of functions, from direct killing of infected cells
by cytotoxic T-cells, to providing T-cell help by secreting
cytokines and chemokines that recruit and activate other
cells and assist in antibody production. Formation of an IS
facilitates much of this. One of the best-characterised
synapses is that between antigen presenting cells (APC)
and T-cells (3,4). Most T-lymphocytes are naı̈ve or resting
memory cells and must first become activated themselves. T-cell activation is mediated largely by T-cell receptor (TCR) binding to peptide that is associated with major
histocompatibility complex (pMHC) displayed on the surface of an APC. If recognised by the T-cell expressing the
receptor specific for that antigen-MHC complex, TCR
cross-linking transduces signals that cause transcriptional
up-regulation and cell proliferation. T-cell activation
requires a threshold of pMHC–TCR interactions, estimated
to be between 50 and 300 (3,5) and this helps ensure that
high-affinity antigen-specific T-cells respond appropriately.
The synapse gains stability through co-receptor interactions such as the integrin Lymphoctye Function-associated
Adhesion molecule (LFA-1) on the T-cell binding to its
cognate ligand Intercellular Adhesion Molecule-1 (ICAM1) on the opposing cell, and CD28 interacting with B7 (6). It
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appears that the initial contact between a T-cell and an
APC is antigen-independent and adhesion molecule binding precedes the specific pMHC–TCR interactions (7).
Signal transduction by the TCR/CD3 complex and costimulation by CD28 and LFA-1 directs cytoskeletal remodelling
in the synaptic T-cell (3,8,9). This in turn recruits more
receptors to the synapse, increasing stability and amplifying activation signals. A series of elegant studies have
demonstrated the complexity of molecular arrangements
at the IS (3,10,11). At the earliest stages the supramolecular activation cluster (SMAC) consists of a central core of
LFA-1-ICAM, which is surrounded by a ring of TCR-pMHC
molecules. In the space of minutes this inverts and the
TCR-pMHC becomes central (cSMAC), surrounded by
adhesion molecules at the periphery (pSMAC). In this
mature synapse, the microtubule organising centre
(MTOC) is positioned proximally and other accessory proteins, such as the adaptor protein talin and protein tyrosine
kinases including Lck, ZAP-70 and PKCy are also recruited
(10–12) (also see Figure 1). In addition to transcriptional
activation in the T-cell, the IS facilitates the transfer of
molecules between cells by directed secretion into the
synaptic cleft. Cytotoxic CD8þ T-cells use the IS to direct
target cell killing by exocytosis of lytic granules and perforin (13) whereas CD4þ T-cells can secrete activating
cytokines such as interleukin-5 across the synapse (14).
What is a Virological Synapse?
In order to initiate infection, viruses must adhere to surface
receptors on target cells, and then traverse the plasma
membrane to gain access to the host cell replicative
machinery. The classic model of virus entry describes
cell-free virion binding and entry with little, if any, active
contribution to infection by the target cell. Some viruses,
Figure 1: Generalised molecular interactions taking place between cells in the immunological synapse (top) and the virological
synapse (bottom). Some of the interactions are probably shared between the two types of synapse, such as LFA-1-ICAM-1 and LFA-1talin-actin, whereas others are specific for each type of synapse.
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Retroviruses and the Virological Synapse
however, move by direct passage between infected and
uninfected cells (15), a process that may be particularly
important in tissues where cells are in close contact, such
as within epithelial and endothelial surfaces, lymphoid
organs and neuronal axons. Although this process is poorly
understood, direct cell–cell transmission has a number of
probable advantages for viruses. Firstly, it allows more
rapid replication kinetics than free virus infection by speeding up or obviating a rate-limiting step in replication–viral
attachment. Secondly, it may allow the virus to evade
aspects of the humoral immune response such as neutralising antibody and complement. Retroviruses, including
the Human T-cell Leukaemia Virus type-1 (HTLV-1) and
the Human Immunodeficiency virus type-1 (HIV-1) can
spread by direct cell–cell transfer. HTLV-1 appears to use
this process as its primary mode of spread between and
within hosts (16), whereas the relative contributions of
cell–cell vs. cell-free dissemination in HIV-1 infection is
unknown. Both of these viruses infect T-cells that are
able to form IS contacts. The existence of synapse-like
structures serving to facilitate HIV-1 dissemination had
been suggested in the past (15,17), and there were hints
that HIV-1 might require a functional actin cytoskeleton
during virus infection or HIV-1-mediated fusion (18,19).
However, no detailed evidence had been put forward to
support the concept of a retrovirally driven synapse. Over
the past year, three papers have shed light on how these
two viruses may exploit interactions taking place between
immune cells resulting in the formation of a ‘virological
synapse’ (20–22). Based on these studies we tentatively
define the virological synapse (VS) as a cytoskeletondependent, stable adhesive junction across which virus is
transmitted by directed transfer. The VS forms in response
to contact between virally infected (effector) and permissive, uninfected (target) immune cells, and contains viral
antigens and cellular receptors colocalised at the conjugate
interface (see Figure 1). In the case of HIV-1 (21), viral
receptors and adhesion molecules are recruited into the
target cell-side of the synapse in a cytoskeleton-dependent
manner. In the effector cell, the core proteins (Gag) are
focussed at the synapse and antigen rapidly transfers
across the synaptic junction into the target cell, in a
microtubule-dependent manner.
The HIV-1 DC-T Cell VS
HIV-1 is the cause of AIDS and currently infects approximately 40 million people worldwide. Although the predominant mode of transmission is via sexual contact,
meaning that the mucosae and associated tissues are
the initial targets of infection, the major source of virus
production in HIV-1-infected individuals is CD4þ T-lymphocytes. Permissive T-cells express the HIV-1 entry receptors
CD4 and a chemokine receptor (CKR); either or both CCR5
and CXCR4 (23). HIV-1 engages these receptors in a
two-step process via the viral surface glycoprotein (Env)
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subunit gp120 (24). CD4-gp120 engagement induces CKR
binding, which in turn activates the Env transmembrane
subunit gp41, promoting fusion of the Env-containing and
target cell membranes. The viral core is then released into
the cytoplasm for subsequent steps including reverse transcription and proviral integration into the host cell genome.
CKR usage defines the cellular tropism of HIV: CCR5-using
viruses infect monocytes/macrophages and activated and
memory CD4þ T-cells, whereas CXCR4-using isolates
infect predominantly naı̈ve CD4þ T-cells that are the
major CD4þ subset circulating in the periphery. Macrophages and dendritic cells (DC) are also targets for HIV-1
uptake and infection (25,26). DC can be divided into
mature and immature subsets; HIV can enter and replicate
efficiently in immature DC but can be captured by, but
replicate only inefficiently in, mature DC (27). Productive
infection of DC by HIV-1 is mediated by Env–CD4/CCR5
interactions (27), but virus uptake can also take place via
cognate recognition of adhesion molecules in the virus
envelope (28) or glycans on gp120 by lectins, most notably
the C-type lectin DC-SIGN (29).
A prominent model for sexual transmission of HIV-1 is that
DC acquire HIV-1 in the mucosae and transmit the virus to
T cells in the secondary lymphoid tissue (30). Infection of
CD4þ T-cells in trans by DC-captured HIV-1 was found to
be more efficient than infection with cell-free virus (30).
Until recently it was not clear how DC acquired and transmitted HIV-1, but recent results show that both lectinmediated acquisition (31) and infection (25) can lead to
efficient infection of T-cells. As mentioned above, DC
interact intimately with T-cells in both antigen-dependent
and independent ways, resulting in cytoskeleton-dependent receptor recruitment to the cellular interface (7). A
significant advance in our understanding of the role of DC
in transmitting HIV-1 infection was made by McDonald and
colleagues (22), who first described an HIV-1-induced
synapse. The synapse in this study was referred to as an
‘infectious synapse’ but for consistency in this review we
shall use the term virological synapse. Using fluorescent
(GFP)-tagged HIV-1 virions, it was observed that in
response to contact between an HIV-1-pulsed (effector)
DC and a (target) T-cell, the DC rapidly recruited virus to
the conjugate interface. CD4, CCR5 and LFA-1 were partially polarised to the interface on the T-cell and transfer of
HIV-1 into the target cell took place across the synapse.
HIV-1 recruitment to the synapse in the DC was resistant
to protease treatment, indicating that the virions were
within an intracellular compartment, which was trafficked
to the synapse. Although the DC intracellular compartment
containing HIV-1 has not been formally identified, recent
work suggests that the virus localises within multivesicular
bodies (MVB) for translocation to the synapse (T. Hope,
personal communication). MVB are intracellular compartments consisting of membrane-bound vesicles that perform a number of endosomal functions, including transport
of cytosolic protein and membrane out of the cell via
exocytosis (32). This result is consistent with reports that
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HIV-1 budding into MVB followed by exocytosis may be
the principal mode of viral egress from macrophages
(33,34). Given the shared monocytic lineage between
macrophages and the monocyte-derived (mDC) used in
the McDonald study, it is likely that a similar mechanism
pertains to mDC. The idea that HIV-1 in DC may be using
vesicular transport is supported by data showing that
monomeric gp120 is not present in the same vesicles as
whole virus within pulsed DC and that HIV may alter endolysosomal trafficking to avoid degradation by lysosomes
(26).
The HIV-1 T Cell VS
The rapid kinetics of HIV-1 infection of target T-cells via
direct transfer from infected T-cells is well-established
(35–37), although the molecular details of this process
had not been elucidated. The movement of viral antigens
and genomic RNA between cells followed by the de novo
synthesis of viral DNA and protein in the target cell testify
to the rapid kinetics and productive nature of this mode of
viral spread (35,38). Some time ago we observed that CD4
and Env rapidly cocluster at the site of target-effector T-cell
contact (39). We have recently followed this up and
describe the formation of an HIV-1-induced VS between
T-cells (21). We observed that if a T-cell line (Jurkat)
infected with a CXCR4-using strain of HIV was incubated
with uninfected primary CD4þ/CXCR4þ T-cells negatively
enriched from peripheral blood, there was rapid recruitment to the cell–cell contact surface of CD4, CXCR4,
talin, actin and LFA-1 on the target cell (Figure 2). This
was concomitant with recruitment of Env and Gag to the
site of cell contact in the effector cell. Kinetic studies
showed that LFA-1 and viral receptor recruitment in the
target cell was rapid (recruitment in 50% of conjugates
in < 30 min) and so perhaps required active transport of
receptors to the interface, as opposed to relying on passive diffusion. Confirmation of a role for cytoskeletal
mobilization of receptors came from studies demonstrating enrichment of F-actin in the target cell at the interface
and inhibition of receptor recruitment when the target cells
were treated with inhibitors of actin remodeling or myosinmotor protein function. In the infected T-cell, Env and Gag
Figure 2: Schematic diagram of the virological synapse formed between a retrovirally infected (effector) and an uninfected
(target) T-cell. The cell–cell contact zone contains tight junctions and, in the case of the HIV-1 VS, a synaptic cleft into which virions are
released from the effector cell. The HTLV-1 VS may differ from the HIV-1 VS: there is no evidence for HTLV-1 virion budding or release or
of a synaptic cleft (C. Bangham, unpublished results). The MTOC is polarised towards the site of cell–cell contact and viral Gag may be
associated with, and be transported along, microtubules. Figure based on results presented in (20–22).
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Retroviruses and the Virological Synapse
recruitment appears to be induced in response to cell–cell
contact and to require components of the actin and tubulin
cytoskeleton ((21) and our unpublished results). The T-cellT-cell VS facilitated transfer of HIV-1 into the previously
uninfected target cell by promoting directed budding of
virus into the synaptic cleft, probably followed by fusion
of virions with the target cell plasma membrane. Polarised
budding of HIV-1 in cell–cell conjugates has been previously observed by electron microscopy, and implies a
mechanism for targeting virus to the site of cell contact
(17,40,41). Unlike DC–T-cell clustering, which is frequently
observed under normal, uninfected conditions, CD4þ
T-cells do not often form stable antigen-independent
contacts with each other. Although weak cell–cell contacts
may form randomly between T-cells, a specific trigger is
probably required to enhance and stabilise adhesion. To
test the hypothesis that the trigger may be engagement of
CD4 and CXCR4 on the surface of a target cell by Env on
the effector cell, we tested the effects of blocking antibodies and pharmacological inhibitors on the VS. Antibody
and drug-mediated inhibition of Env-CD4 and Env-CXCR4
binding blocked VS formation and reduced conjugates
forming between T-cells.
These two studies (21,22) confirm the general concept of a
viral synapse, and are important for our understanding of
the earliest stages of transmission, dissemination and
immune evasion by HIV-1. Since DC are one of the first
cells to encounter incoming virus at the mucosal surface,
where most HIV-1 transmission occurs, the VS would help
protect the virus from immune surveillance and allow it to
rapidly and efficiently gain access to the major target of
HIV-1 infection, the CD4þ T-cell. Synaptic transfer of HIV-1
between T-cells would likewise help the virus spread efficiently within secondary lymphoid tissue. Moreover, this
model may help explain an interesting paradigm in HIV
pathogenesis – the preferential infection of virus-specific
CD4þ T-cells by HIV-1 (42).
The HTLV-I T Cell VS
A detailed description of a VS was first published in the
context of HTLV-I infection (20). HTLV-I is an oncogenic
human retrovirus that infects 10–20 million people worldwide. Although only rarely associated with disease,
approximately 2–3% of infected individuals develop an
adult T-cell leukaemia and another 2–3% suffer from
chronic inflammatory syndromes. Like HIV-1, HTLV-I is
also T-cell-tropic but infects both CD4þ and CD8þ T-cells
and spread between and within individuals is primarily by
infected lymphocytes with little, if any, contribution from
cell-free virus (16).
Igakura and workers (20) described a VS that forms during
contact between an HTLV-I infected and an uninfected
T-cell. Similar to the HIV-1 VS, cell–cell contact promoted
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clustering of HTLV-1 Env and Gag within the effector
cell and talin within the target cell to the site of cell–cell
contact. In unconjugated infected cells the HTLV-1 core
proteins Gag p19 and p15 are arranged in clusters near the
plasma membrane and Env is uniformly distributed on the
cell surface. Target–effector cell interactions induced rapid
(< 30 min) polarization of Gag and Env to the cell–cell
junction and transfer of Gag into the target cell within 2 h.
Fluorescence in situ hydridisation studies showed that Gag
movement into the target cell was coordinated with
transfer of the HTLV-1 RNA genome. Similar to the
formation of an IS between a CD8þ CTL and its target
(13), MTOC polarisation towards the synapse also occurs
in the effector cell in the HTLV-1 VS. Igakura et al. (20)
point out that MTOC movement is not triggered by
specific T-cell receptor recognition of HTLV-1 antigen in
the infected cell and does not represent a T-cell IS, but a
VS. However, similar to a T-cell IS, there is a higher order
level of structure to the HTLV-1 VS. The actin adaptor
protein talin is recruited in a percentage of VS conjugates
into a ring-like structure reminiscent of a pSMAC in the
IS (20).
Recently, the glucose transport protein GLUT-1 has been
identified as an entry receptor for HTLV-1 (43) and it will
now be interesting to examine the role of the target cell in
VS formation. By analogy with the HIV-1 T-cell synapse, it
might be expected that the Env clustering in the effector
cell will be mirrored by enrichment of GLUT-1 in the target
cell at the interface. Indeed, preliminary results suggest
that this is the case (D. Brighty, personal communication).
What Directs VS Formation?
VS formation requires the active participation of the cell
cytoskeleton. A major unanswered question is what triggers VS formation and is it a mechanism common to both
HIV-1 and HTLV-1-induced synapses and DC and T-cells?
Let us first look at the target cell. In the IS the signalling
cascade that directs receptor recruitment has been well
studied. TCR/CD3-pMHC binding leads to lck-mediated
phosphorylation of the cytoplasmic tail of CD3 and subsequent recruitment of activated ZAP-70. This in turn phosphorylates other adaptors and the signalling cascade
culminates in recruitment of actin, actin-anchored receptors and the MTOC to the site of cell–cell contact. CD4
signalling by p56lck contributes to IS formation (3) and
costimulation by LFA-1 can also reorganise F-actin and
recruit additional high-affinity adhesion molecules to the
synapse (9). It is unlikely that TCR signalling plays a determinant role in the VS since the TCR was not actively
recruited into the HIV-1 T-cell synapse (21) and the frequent realignment of the MTOC in HTLV-1-infected cells is
not consistent with antigen-specific recognition by a TCR
(20). However, TCR-mediated recognition of target cells
should not be ruled out as a ‘cofactor’ to VS formation
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since both HIV-1 and HTLV-1 preferentially infect virusspecific T-cells (42,44,45). Env-receptor engagement is
central to the HIV-1 VS since blocking these interactions
with inhibitors abrogated VS assembly ((21) and unpublished results). Whether this is because VS formation
requires signals to be transduced through CD4 and/or the
CKR in response to Env binding, or Env-receptor binding
simply mediates sufficiently tight conjugate formation to
allow other proteins to interact and elaborate a synapse is
unclear. Signal transduction by CD4 (via p56lck) and CKRs
is well documented and evidence exists that gp120
engagement of these receptors can initiate signalling
cascades (46–48). CKRs are G-protein coupled receptors
and can transduce signals in a G-protein-dependent or
-independent manner and this is necessary for cellular polarization and chemotaxis (49). Interestingly, CKR-mediated
signalling can activate integrins by inducing conformational
changes that force a switch from a low-affinity to a highaffinity state (50) and this is necessary for efficient ligand
binding. Moreover, integrin activation modifies its association with the cytoskeleton, and the increase in lateral mobility facilitates rapid integrin clustering (51) and subsequent
integrin-mediated actin remodelling (9). Integrin activation
is a particular requirement for naı̈ve and resting T-cells,
which express the low-avidity, low-affinity form in the
absence of stimulation. This suggests that LFA-1 and/or
other integrins may both initiate and require triggering of
actin remodelling and recruitment of other receptors. In
this respect, integrins appear to be a common link
between the IS and VS. Integral to HIV-1 VS assembly is
the actin-mediated recruitment of CD4 and CKRs. Association of CD4 (52) and CXCR4 (53) with actin has been
documented, suggesting that they may be recruited
directly by F-actin polarising to the site of cell–cell contact.
Alternatively, these receptors may be recruited via their
association with detergent insoluble lipid microdomains
(DIMs). We have observed coalescence of GM1-rich
domains to the HIV-1 VS in target T-cells (unpublished
results). Both CD4 and CXCR4 are at least partially compartmentalised within DIMs (54,55), and there is evidence
to support a link, via annexin-II, between DIMs and the
actin cytoskeleton (56). Future studies will investigate the
role of signalling via CD4, CKRs and integrins in the HIV-1
VS and GLUT-1 and integrins in the HTLV-1 VS.
Initiation of events relating to VS formation within the
effector cell is obscure. Intracellular HIV particles were
recruited to the site of cell–cell contact in DC–T-cell
conjugates (22), and HIV-1 and HTLV-1 Env and Gag
polarise to the VS in infected T-cells (20,21). It appears
that the infected cell is able to detect cell–cell contact
and traffic viral antigens to the VS, but the trigger for
this is unknown. One speculative pathway might be via
signalling associated with a tyrosine motif located
within the cytoplasmic tail of HIV-1 gp41: mutation of
this motif reduced polarisation of p24 and directed virus
budding in the cell and interfered with cell–cell spread
(40). Tyrosine-based motifs in retroviral transmembrane
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glycoproteins have been shown to signal in infected
cells, making this a plausible hypothesis (57). Ligation
of plasma membrane-associated Env by receptors on
the target cell might trigger such a pathway. For the
DC-T-cell viral synapse it is becoming clearer that this
probably involves re-routing of HIV-1-containing intracellular vesicles, potentially MVB, through the exocytosis pathway. As mentioned above, it seems likely that
the virus is subverting a normal intercellular vesicular
communication pathway to facilitate its own dissemination between cells. Whether there is a role for the
exocytic pathway in transporting HIV proteins to the
T-cell viral synapse is untested and cannot be excluded,
but HIV-1 is not thought to bud into intracellular vesicles
in T-cells, but to assemble under and bud out directly
from the plasma membrane. In this model, Env is
trafficked to the plasma membrane via the secretory
pathway and is enriched in lipid rafts (40,58). Viral
components then assemble under the patches of Env,
ultimately resulting in foci of nascent virions budding
through rafts. The recruitment of viral Gag to the site
of assembly may be along microtubules; this concept is
supported by reorientation of the MTOC proximal to the
VS in a high frequency of conjugates ((20) and our
unpublished results). CD4þ T-cells are not usually
polarised but they can become so after activation during
chemotaxis or in response to cell–cell contact (59) and
this appears to impact on sites of viral release. In
summary, polarised virus assembly and budding at the
T-cell VS may require both virus-specific signals and
normal cellular responses to synapse elaboration. It
will be interesting to investigate whether the recently
described cellular machinery that assists in viral
budding, termed the ESCRT pathway (60–62), plays a
role in polarised HIV-1 exit from T-cells. Understanding
the role of the effector cell in the VS is perhaps the
most exciting challenge in this area because of the
potential to provide new targets for antiviral therapies.
Conclusions
Many intracellular pathogens including viruses, bacteria
and parasites are able to hijack elements of the host cell
cytoskeleton to assist in entry, exit and cytoplasmic trafficking. What then are the special features of the VS?
Because viruses are obligate intracellular parasites, they
appear to be able to manipulate the infected cell cytoskeleton
from within to promote and polarise viral egress. If the
infected cells are already polarised, such as in epithelial
monolayers, then the direction of virus movement will be
predetermined. When the cells involved are members of
the immune system, the machinery for communication
between them pre-exists, but is not activated. It appears
that in the case of viruses that infect immune cells such as
HIV-1 and HTLV-1, a combination of virus–receptor interactions and cognate immune receptor interactions are
required to activate and regulate cell–cell movement of virus.
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Acknowledgments
We thank Charles Bangham, Tom Hope and David Brighty for critical reading of the manuscript and permission to cite unpublished results. Work on
the HIV-1 T cell synapse described in this review was supported by MRC
MDP grant G0100137.
References
1. Tanner SB, Örfelt B, Pirinen NJ, McCann FJ, Magee AL, Davis DM.
Control of immune response by trafficking cell surface proteins,
vesicles and lipid rafts to and from the immunological synapse. Traffic
2004;5:in press.
2. Dustin ML, Colman DR. Neural and immunological synaptic relations.
Science 2002;298:785–789.
3. Grakoui A, Bromley SK, Sumen C, Davis MM, Shaw AS, Allen PM,
Dustin ML. The immunological synapse: a molecular machine controlling T cell activation. Science 1999;285:221–227.
4. Krummel MF, Davis MM. Dynamics of the immunological synapse:
finding, establishing and solidifying a connection. Curr Opin Immunol
2002;14:66–74.
5. Peterson DA, DiPaolo RJ, Kanagawa O, Unanue ER. Cutting edge:
negative selection of immature thymocytes by a few peptide-MHC
complexes: differential sensitivity of immature and mature T cells.
J Immunol 1999;162:3117–3120.
6. Viola A, Schroeder S, Sakakibara Y, Lanzavecchia A. T lymphocyte
costimulation mediated by reorganization of membrane microdomains.
Science 1999;283:680–682.
7. Revy P, Sospedra M, Barbour B, Trautmann A. Functional antigenindependent synapses formed between T cells and dendritic cells.
Nat Immunol 2001;2:925–931.
8. Wulfing C, Davis MM. A receptor/cytoskeletal movement triggered by
costimulation during T cell activation. Science 1998;282:2266–2269.
9. Porter JC, Bracke M, Smith A, Davies D, Hogg N. Signaling through
integrin LFA-1 leads to filamentous actin polymerization and remodeling,
resulting in enhanced T cell adhesion. J Immunol 2002;168:6330–6335.
10. Monks CR, Freiberg BA, Kupfer H, Sciaky N, Kupfer A. Threedimensional segregation of supramolecular activation clusters in
T cells. Nature 1998;395:82–86.
11. Freiberg BA, Kupfer H, Maslanik W, Delli J, Kappler J, Zaller DM,
Kupfer A. Staging and resetting T cell activation in SMACs. Nat
Immunol 2002;3:911–917.
12. Lowin-Kropf B, Shapiro VS, Weiss A. Cytoskeletal polarization of T cells
is regulated by an immunoreceptor tyrosine-based activation motifdependent mechanism. J Cell Biol 1998;140:861–871.
13. Stinchcombe JC, Bossi G, Booth S, Griffiths GM. The immunological
synapse of CTL contains a secretory domain and membrane bridges.
Immunity 2001;15:751–761.
14. Kupfer A, Kupfer H. Imaging immune cell interactions and functions.
Smacs Immunol Synapse Semin Immunol 2003;15:295–300.
15. Johnson DC, Huber MT. Directed egress of animal viruses promotes
cell-to-cell spread. J Virol 2002;76:1–8.
16. Bangham CR. The immune control and cell-to-cell spread of human
T-lymphotropic virus type 1. J General Virol 2003;84:3177–3189.
17. Fais S, Capobianchi MR, Abbate I, Castilletti C, Gentile M, Cordiali Fei P,
Ameglio F, Dianzani F. Unidirectional budding of HIV-1 at the site of
cell-to-cell contact is associated with co-polarization of intercellular
adhesion molecules and HIV-1 viral matrix protein. AIDS 1995;9:
329–335.
18. Iyengar S, Hildreth JE, Schwartz DH. Actin-dependent receptor
colocalization required for human immunodeficiency virus entry into
host cells. J Virol 1998;72:5251–5255.
Traffic 2004; 5: 643–650
19. Frey S, Marsh M, Gunther S, Pelchen-Matthews A, Stephens P,
Ortlepp S, Stegmann T. Temperature dependence of cell-cell fusion
induced by the envelope glycoprotein of human immunodeficiency
virus type 1. J Virol 1995;69:1462–1472.
20. Igakura T, Stinchcombe JC, Goon PK, Taylor GP, Weber JN, Griffiths GM,
Tanaka Y, Osame M, Bangham CR. Spread of HTLV-I between lymphocytes by virus-induced polarization of the cytoskeleton. Science 2003;299:
1713–1716.
21. Jolly C, Kashefi K, Hollinshead M, Sattentau QJ. HIV-1 Cell to cell
transfer across an Env-induced, actin-dependent synapse. J Exp Med
2004;199:283–293.
22. McDonald D, Wu L, Bohks SM, KewaI, Ramani VN, Unutmaz D,
Hope TJ. Recruitment of HIV and its receptors to dendritic cell-T cell
junctions. Science 2003;300:1295–1297.
23. Berger EA. HIV entry and tropism: the chemokine receptor connection.
AIDS 1997;11(Suppl. A):S3–S16.
24. Sattentau QJ. HIV gp120: double lock strategy foils host defences.
Structure 1998;6:945–949.
25. Pope M, Gezelter S, Gallo N, Hoffman L, Steinman RM. Low levels of
HIV-1 infection in cutaneous dendritic cells promote extensive viral
replication upon binding to memory CD4þ T cells. J Exp Med 1995;
182:2045–2056.
26. Turville SG, Santos JJ, Frank I, Cameron PU, Wilkinson J,
Miranda-Saksena M, Dable J, Stossel H, Romani N, Piatak M Jr,
LifsonJD, Pope M, Cunningham AL. Immunodeficiency virus uptake,
turnover, and 2-phase transfer in human dendritic cells. Blood
2004;103:2170–2179.
27. Granelli-Piperno A, Delgado E, Finkel V, Paxton W, Steinman RM.
Immature dendritic cells selectively replicate macrophagetropic
(M-tropic) human immunodeficiency virus type 1, while mature cells
efficiently transmit both M- and T-tropic virus to T cells. J Virol 1998;
72:2733–2737.
28. Tsunetsugu-Yokota Y, Yasuda S, Sugimoto A, Yagi T, Azuma M,
Yagita H, Akagawa K, Takemori T. Efficient virus transmission
from dendritic cells to CD4þ T cells in response to antigen depends
on close contact through adhesion molecules. Virology 1997;239:
259–268.
29. Turville SG, Cameron PU, Handley A, Lin G, Pohlmann S, Doms RW,
Cunningham AL. Diversity of receptors binding HIV on dendritic cell
subsets. Nat Immunol 2002;3:975–983.
30. van Kooyk Y, Geijtenbeek TB. DC-SIGN: escape mechanism for
pathogens. Nat Rev Immunol 2003;3:697–709.
31. Geijtenbeek TB, Kwon DS, Torensma R, van Vliet SJ, van Duijnhoven GC,
Middel J, Cornelissen IL, Nottet HS, KewaI, Ramani VN, Littman DR,
Figdor CG, van Kooyk Y. DC-SIGN, a dendritic cell-specific HIV-1binding protein that enhances trans-infection of T cells. Cell 2000;100:
587–597.
32. Denzer K, Kleijmeer MJ, Heijnen HF, Stoorvogel W, Geuze HJ.
Exosome: from internal vesicle of the multivesicular body to intercellular signaling device. J Cell Sci 2000;113 Part 19:3365–3374.
33. Raposo G, Moore M, Innes D, Leijendekker R, Leigh-Brown A,
Benaroch P, Geuze H. Human macrophages accumulate HIV-1
particles in MHC II compartments. Traffic 2002;3:718–729.
34. Pelchen-Matthews A, Kramer B, Marsh M. Infectious HIV-1 assembles
in late endosomes in primary macrophages. J Cell Biol 2003;
162:443–455.
35. Sato H, Orenstein J, Dimitrov D, Martin M. Cell-to-cell spread of HIV-1
occurs within minutes and may not involve the participation of virus
particles. Virology 1992;186:712–724.
36. Dimitrov DS, Willey RL, Sato H, Chang LJ, Blumenthal R, Martin MA.
Quantitation of human immunodeficiency virus type 1 infection
kinetics. J Virol 1993;67:2182–2190.
37. Carr JM, Hocking H, Li P, Burrell CJ. Rapid and efficient cell-tocell transmission of human immunodeficiency virus infection from
649
Jolly and Sattentau
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
monocyte-derived macrophages to peripheral blood lymphocytes.
Virology 1999;265:319–329.
Li P, Burrell CJ. Synthesis of human immunodeficiency virus DNA in a
cell-to-cell transmission model. AIDS Res Hum Retroviruses 1992;8:
253–259.
Sattentau QJ, Moore JP. The role of CD4 in HIV binding and entry.
Philos Trans R Soc Lond B Biol Sci 1993;342:59–66.
Deschambeault J, Lalonde JP, Cervantes-Acosta G, Lodge R, Cohen EA,
Lemay G. Polarized human immunodeficiency virus budding in
lymphocytes involves a tyrosine-based signal and favors cell-to-cell viral
transmission. J Virol 1999;73:5010–5017.
Pearce-Pratt R, Malamud D, Phillips DM. Role of the cytoskeleton in
cell-to-cell transmission of human immunodeficiency virus. J Virol
1994;68:2898–2905.
Douek DC, Brenchley JM, Betts MR, Ambrozak DR, Hill BJ,
Okamoto Y, Casazza JP, Kuruppu J, Kunstman K, Wolinsky S,
Grossman Z, Dybul M, Oxenius A, Price DA, Connors M, et al. HIV
preferentially infects HIV-specific CD4þ T cells. Nature 2002;
417:95–98.
Manel N, Kim FJ, Kinet S, Taylor N, Sitbon M, Battini JL. The ubiquitous
glucose transporter GLUT-1 is a receptor for HTLV. Cell 2003;
115:449–459.
Hanon E, Hall S, Taylor GP, Saito M, Davis R, Tanaka Y, Usuku K,
Osame M, Weber JN, Bangham CR. Abundant tax protein expression
in CD4þ T cells infected with human T-cell lymphotropic virus type I
(HTLV-I) is prevented by cytotoxic T lymphocytes. Blood 2000;95:
1386–1392.
Goon PK, Hanon E, Igakura T, Tanaka Y, Weber JN, Taylor GP,
Bangham CR. High frequencies of Th1-type CD4 (þ) T cells
specific to HTLV-1 Env and Tax proteins in patients with HTLV-1-associated myelopathy/tropical spastic paraparesis. Blood 2002;99:3335–
3341.
Benkirane M, Jeang KT, Devaux C. The cytoplasmic domain of CD4
plays a critical role during the early stages of HIV infection in T-cells.
EMBO J 1994;13:5559–5569.
Davis CB, Dikic I, Unutmaz D, Hill CM, Arthos J, Siani MA, Thompson DA,
Schlessinger J, Littman DR. Signal transduction due to HIV-1 envelope
interactions with chemokine receptors CXCR4 or CCR5. J Exp Med
1997;186:1793–1798.
Cicala C, Arthos J, Selig SM, Dennis G, Hosack DA, Van Ryk D,
Spangler ML, Steenbeke TD, Khazanie P, Gupta N, Yang J, Daucher M,
Lempicki RA, Fauci AS. HIV envelope induces a cascade of cell signals in
non-proliferating target cells that favor virus replication. Proc Natl Acad
Sci U S A 2002;99:9380–9385.
650
49. Pierce KL, Premont RT, Lefkowitz RJ. Seven-transmembrane receptors. Nat Rev Mol Cell Biol 2002;3:639–650.
50. Laudanna C, Kim JY, Constantin G, Butcher E. Rapid leukocyte integrin
activation by chemokines. Immunol Rev 2002;186:37–46.
51. Stewart MP, McDowall A, Hogg N. LFA-1-mediated adhesion is regulated by cytoskeletal restraint and by a Ca2þ -dependent protease,
calpain. J Cell Biol 1998;140:699–707.
52. Kinch MS, Strominger JL, Doyle C. Cell adhesion mediated by CD4 and
MHC class II proteins requires active cellular processes. J Immunol
1993;151:4552–4561.
53. Rey M, Vicente-Manzanares M, Viedma F, Yanez-Mo M, Urzainqui A,
Barreiro O, Vazquez J, Sanchez-Madrid F. Cutting edge: association of
the motor protein nonmuscle myosin heavy chain-IIA with the C
terminus of the chemokine receptor CXCR4 in T lymphocytes. J Immunol 2002;169:5410–5414.
54. Cerny J, Stockinger H, Horejsi V. Noncovalent associations of T
lymphocyte surface proteins. Eur J Immunol 1996;26:2335–2343.
55. Manes S, Mira E, Gomez-Mouton C, Lacalle RA, Keller P, Labrador JP,
Martinez AC. Membrane raft microdomains mediate front-rear polarity
in migrating cells. EMBO J 1999;18:6211–6220.
56. Harder T, Kellner R, Parton RG, Gruenberg J. Specific release of
membrane-bound annexin II and cortical cytoskeletal elements by
sequestration of membrane cholesterol. Mol Biol Cell 1997;8:533–545.
57. Beaufils P, Choquet D, Mamoun RZ, Malissen B. The (YXXL/I)/2
signalling motif found in the cytoplasmic segments of the bovine
leukaemia virus envelope protein and Epstein–Barr virus latent
membrane protein 2A can elicit early and late lymphocyte activation
events. EMBO J 1993:12:5105–5112.
58. Nguyen DH, Hildreth JE. Evidence for budding of human immunodeficiency virus type 1 selectively from glycolipid-enriched membrane
lipid rafts. J Virol 2000;74:3264–3272.
59. Sanchez-Madrid F, del Pozo MA. Leukocyte polarization in cell migration and immune interactions. EMBO J 1999;18:501–511.
60. Garrus JE, von Schwedler UK, Pornillos OW, Morham SG, Zavitz KH,
Wang HE, Wettstein DA, Stray KM, Cote M, Rich RL, Myszka DG,
Sundquist WI. Tsg101 and the vacuolar protein sorting pathway are
essential for HIV-1 budding. Cell 2001;107:55–65.
61. Martin-Serrano J, Zang T, Bieniasz PD. HIV-1 and Ebola virus encode
small peptide motifs that recruit Tsg101 to sites of particle assembly to
facilitate egress. Nat Med 2001;7:1313–1319.
62. von Schwedler UK, Stuchell M, Muller B, Ward DM, Chung HY,
Morita E, Wang HE, Davis T, He GP, Cimbora DM, Scott A,
Krausslich HG, Kaplan J, Morham SG, Sundquist WI. The protein
network of HIV budding. Cell 2003;114:701–713.
Traffic 2004; 5: 643–650