Published online before print January 17, 2008, doi: 10.1161/CIRCRESAHA.107.161653
© 2008 American Heart Association, Inc.
Molecular Medicine |
Vessel Wall–Embedded Dendritic Cells Induce T-Cell Autoreactivity and Initiate Vascular Inflammation
From the Kathleen B. and Mason I. Lowance Center for Human Immunology (J.W.H., K.S., W.M.-K., J.J.G., C.M.W.), Department of Medicine, Emory University School of Medicine, Atlanta, Ga; and Parker H. Petit Institute for Bioengineering and Bioscience (T.L.J., R.M.N.), Georgia Institute of Technology, Atlanta.
Correspondence to Cornelia M. Weyand, MD, PhD, Lowance Center for Human Immunology, Emory University School of Medicine, Room 1003 WMRB, 101 Woodruff Cir, Atlanta, GA 30322. E-mail cweyand{at}emory.edu
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Abstract |
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Human medium-sized and large arteries are targeted by inflammation with innate and adaptive immune responses occurring within the unique microspace of the vessel wall. How 3D spatial arrangements influence immune recognition and cellular response thresholds and which cell populations sense immunoactivating ligands and function as antigen-presenting cells are incompletely understood. To mimic the 3D context of human arteries, bioartificial arteries were engineered from collagen type I matrix, human vascular smooth muscle cells (VSMCs), and human endothelial cells and populated with cells implicated in antigen presentation and T-cell stimulation, including monocytes, macrophages, and myeloid dendritic cells (DCs). Responsiveness of wall-embedded antigen-presenting cells was probed with the Toll-like receptor ligand lipopolysaccharide, and inflammation was initiated by adding autologous CD4+ T cells. DCs colonized the outermost VSMC layer, recapitulating their positioning at the media–adventitia border of normal arteries. Wall-embedded DCs responded to the microbial product lipopolysaccharide by entering the maturation program and upregulating the costimulatory ligand CD86. Activated DCs effectively stimulated autologous CD4 T cells, which produced the proinflammatory cytokine interferon-
and infiltrated deeply into the VSMC layer, causing matrix damage. Lipopolysaccharide-triggered macrophages were significantly less efficacious in recruiting T cells and promoting T-cell stimulation. CD14+ monocytes, even when preactivated, failed to support initial steps of vascular wall inflammation. Innate immune cells, including monocytes, macrophages, and DCs, display differential functions in the vessel wall. DCs are superior in sensing pathogen-derived motifs and are highly efficient in breaking T-cell tolerance, guiding T cells toward proinflammatory and tissue-invasive behavior.
Key Words: inflammation • bioengineered vessel • arteries • immune system • interleukins • dendritic cells • Toll-like receptors
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Introduction |
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Inflammation within the wall layers of medium-sized and large arteries is a critical disease mechanism in atherosclerosis and the vasculitides. In vasculitis, such as Takayasu’s arteritis, giant cell arteritis, and Kawasaki disease, dense inflammatory infiltrates accumulate in the vascular wall, and inflammatory tissue injury progresses swiftly. In contrast, the atherosclerotic inflammatory process is smoldering, progressing over decades.1,2 Regardless of the type of vascular inflammation, inflammatory infiltrates are composed of T lymphocytes, monocytes, macrophages, and dendritic cells (DCs) that interact with vessel wall–resident cells, including vascular smooth muscle cells (VSMCs), endothelial cells, and fibroblasts.1,3–5 DCs derive from 2 sources, the indigenous population of wall-residing DCs or circulating DCs, a mobile force of potent immunoregulators. DCs are key regulators of immune and inflammatory responses that sense microbial infections, cellular debris, and modified metabolites through many pattern recognition receptors.6 In addition, they capture and process antigens, which they present to T lymphocytes.6 DCs are the most powerful antigen-presenting cells (APCs), critically involved in priming immune responses.6 Beyond priming T-cell responses, DCs also control tolerance by transporting self antigens and harmless antigens to lymph nodes.7,8 It is now clear that human medium-sized arteries possess an indigenous DC population that critically contributes to regulating vascular wall inflammation.9 We and others have seen DCs located subendothelially in the intima, but such DCs are patchy in distribution and occur only in large elastic vessels.1,10–12 In contrast, adventitial DC networks are consistently found and extend into arterial branches of 3 to 5 mm diameter, such as temporal arteries. We have been able to trigger such adventitial DCs to initiate vessel wall inflammation in vivo.9 Additionally, DCs have been implicated to play an important role in atherosclerosis.13 Human plaque is occupied by 2 different types of DC, myeloid (mDCs) and plasmacytoid (pDCs) DCs,14–16 both highly efficient in regulating plaque inflammation. Plaque-residing mDCs produce T-cell–attracting chemokines and form clusters with activated T cells.14 pDCs are the major cell type releasing type I interferon (IFN), through which they modulate tissue-damaging T-cell functions, such as killing of VSMCs.15 pDCs and mDCs in the plaque recognize different danger signals but interact with each other, amplifying inflammatory responses.17
Monocytes and macrophages do not indigenously reside in the vessel wall; they must be recruited to partake in intramural infiltrates and are critically important in the atherosclerotic plaque.18 Here, they store and modify deposited lipids and release enzymes, such as metalloproteinases, that contribute to tissue damage.18 Whether monocytes and tissue macrophages function as APCs, initiating and sustaining activation of adaptive immune responses, is unknown.
The unique vessel wall microenvironment determines cellular functions of both resident and recruited cells in inflammatory lesions.19–22 It has been a challenge to develop experimental systems that faithfully recapitulate the 3D structure and layering of human blood vessels. Because of their significantly smaller body size, rodents lack arteries resembling human macrovessels. It is, however, arteries with a diameter of 3 to 30 mm that display susceptibility to atherosclerosis and vasculitis. Here, we have used bioartificial arteries engineered to mimic the size and structural dimensions of human arteries and have examined components necessary for the induction of vessel wall inflammation. To recapitulate patient conditions in vivo, we have tested how T cells can be turned into proinflammatory and tissue-destructive effector cells. Specifically, we have compared how different types of APCs, including monocytes, macrophages, and DCs, sense danger signals and direct T cells toward proinflammatory effector functions. Here we report that DCs have excellent APC function in the specialized vessel wall microenvironment. When stimulated with pathogen-derived motifs, such as the Toll-like receptor (TLR) ligand lipopolysaccharide (LPS), DCs differentiate into potent T-cell activators, such that T-cell autoreactivity occurs in the vascular wall. DCs by far outperform differentiated macrophages as APCs, and monocytes fail to upregulate essential surface receptors, such that they cannot promote intramural T-cell activation.
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Materials and Methods |
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Cell Isolation
Monocytes and CD4 T cells were purified from peripheral blood mononuclear cells of healthy volunteers by magnetobead separation (Miltenyi Biotec). To generate macrophages, purified CD14+ cells were cultured in serum-free macrophage-specific media (Macrophage-SFM, Invitrogen) supplemented with 800 U/mL granulocyte macrophage colony–stimulating factor (R&D) for 6 days. Fluorescence-activated cell sorting analysis demonstrated high surface densities of CD11c, CD14, and HLA-DR. DCs were generated from CD14+ precursor cells by culture with 800 U/mL granulocyte macrophage colony–stimulating factor and 1000 U/mL interleukin (IL)-4 (both R&D Systems) for 6 days. They displayed typical DC morphology and were negative for CD14 but expressed high levels of HLA-DR. The Emory Institutional Review Board approved the protocol, and all donors provided informed consent.
Engineering of Bioartificial Arteries
Pilot experiments were conducted with rat VSMCs aimed at optimizing tubular construct engineering. Immune recognition events were studied in bioartificial arteries constructed with human aortic VSMCs. Human aortic VSMCs (Cambrex Bio Science Walkersville Inc) were grown in SmBM with SmGM-2 (Cambrex Bio Science Walkersville Inc) and used between the fifth and ninth passages. Three-dimensional vascular tissue constructs were prepared by embedding VSMCs into a matrix of collagen type I, as reported.23 Briefly, 1 million VSMCs per milliliter were suspended in pepsin-digested 2 mg/mL human or rat tail type I collagen (both BD Biosciences) in 0.02 N acetic acid with 5x concentrated MCDB-131 (Sigma-Aldrich) and 10% FCS and immediately neutralized with 0.1 N sodium hydroxide. Constructs were molded over surface-modified silicone support sleeves and cultured to allow for VSMC circular alignment and collagen matrix contraction. For multilayered constructs, VSMC tubes were closed at both ends with Luer adaptors and human umbilical vein endothelial cells (HUVECs) (Cambrex Bio Science Walkersville Inc; 1x106 cells/5 cm of construct) were injected into the lumen. Tubular constructs were rotated regularly, and nonattached HUVECs were washed off after 24 hours. HUVEC concentrations were chosen to consistently produce an endothelial monolayer, as monitored by immunohistochemistry.
Seeding of Three-Dimensional Constructs With APCs
Equally sized segments of tubular constructs were incubated with increasing numbers of monocytes, macrophages, or DCs (0 to 100 000 cells) for 12 hours. In selected experiments, cells were preactivated with 1.0 µg/mL LPS (Escherichia coli, 0127:B8, Sigma-Aldrich) for 4 hours.
Initiating Vessel Wall Adaptive Immune Responses
Tubular constructs populated with DCs, macrophages, or monocytes were incubated with 3 µg/mL LPS for 12 hours and then cultured with autologous CD4 T cells for 36 hours. Pilot experiments demonstrated that 1x106 CD4 T cells per 4 mm of vascular tube were optimal. Control cultures included constructs without APC and/or LPS stimulation. Constructs were embedded for immunohistochemistry or shock frozen for RNA extraction.
Histology, quantitative PCR, computer-assisted invasion analysis of 3D tubular constructs, and statistical methods are described in the online data supplement at http://circres.ahajournals.org.
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Results |
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Sentinels Populate Bioengineered Human Artery Walls
Bioartificial arteries were engineered by embedding human VSMCs into type I collagen matrix. The constructs gradually shrank over the following 48 hours of stabilization (Figure 1A), a process mediated by circumferential VSMC realignment and matrix contraction. Pilot experiments indicated an optimal ratio of cells to collagen matrix at 1x106 VSMCs per milliliter of liquefied matrix. Cross-sections of tubular constructs showed dense and thick-layered VSMCs (Figure 1B and 1C) forming the medial layer with cell densities resembling that in natural human arteries. The 3D tubes displayed the dimensions of human carotid or subclavian arteries.
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Human large arteries contain indigenous DCs that phenotypically and functionally resemble CD11c-positive myeloid DCs, acquiring CD83 on activation. Consequently, we explored populating bioengineered arteries with such vascular DCs. Three-dimensional tubular constructs were incubated with increasing numbers of DCs generated in vitro from CD14+ DC precursors. DCs, although immature, migrated into the tubes and integrated into the outermost VSMC layer but avoided settling deep into the proximal media (Figure 1E and 1F), recapitulating the positioning of natural vascular DCs. The number of wall-embedded DCs correlated with the number added, without reaching a plateau (Figure 1D). Human carotid, subclavian, mesenteric, and temporal arteries hold 
60 to 100 DCs at the media–adventitia border per 10 µm of vessel (data not shown). Thus, a seeding density of 50 000 to 100 000 DCs per 4 mm of bioartificial artery was chosen to resemble the physiologic numbers of vascular DCs.
Pathogen-Derived Motifs Are Sufficient to Break Tolerance of Vascular DCs and Initiate Vessel Wall Adaptive Immune Responses
The primary function of DCs is to survey the microenvironment for "danger signals," particularly pathogens. To explore whether wall-embedded DCs respond to microbial patterns and regulate adaptive immunity,24 we examined DC activation and DC–T-cell interaction in bioartificial arteries. As a microbial product, we used LPS, the major component of Gram-negative bacterial wall outer membranes and a well-known TLR4 ligand.25 Frequencies of wall-embedded CD11c+ DCs remained unchanged by LPS stimulation (Figure 2A). In the absence of LPS, only a small proportion of CD11c+ DCs in the wall structure were CD83-positive. The fraction of CD83+ DCs doubled after LPS stimulation (Figure 2C).
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After coculture with autologous T cells, only a few CD4 T cells were detected in APC-free arterial constructs (Figure 2D). TLR4 triggering increased the number of T cells recruited to DC-free tubes. However, seeding with DCs markedly enhanced the ability to recruit T cells. Optimal T-cell recruitment was reached in LPS-exposed, DC-populated vessels (Figure 2D). Thus, pathogen-derived molecules, by virtue of stimulating vascular DCs, can induce autologous T-cell accumulation in the medial layer space, a tissue niche that, under physiologic conditions, is not T-cell accessible.
TLR4-Triggered Vascular DCs Positioned in the Three-Dimensional Space of the Vessel Wall Break T-Cell Tolerance and Initiate Adaptive Immune Responses
The TLR4-mediated recruitment of autologous CD4 T cells into the 3D tubes raised the question of whether bacterial infections could facilitate differentiation of vascular DCs, break tolerance, and initiate T-cell priming in the artery. On priming, CD4 T cells upregulate CD40L and transcribe the IFN- gene. To examine whether biologically significant T-cell activation occurs in the bioartificial arteries, constructs were populated with immature DCs, exposed to LPS, and then cocultured with autologous CD4 T cells. As shown in Figure 3, bare tubular constructs lacked LPS-induced transcripts for DC activation products. In the absence of CD4 T cells, wall-embedded DCs transcribed low concentrations of CD83, CCR7, and CD86 transcripts, which increased only slightly (CD83, CCR7) or not at all (CD86) in response to TLR4 stimulation. The combination of TLR4 cross-linking and CD4 T cells, however, created optimal conditions for DC differentiation/maturation. Production of all DC markers, including CD83, CD86, and CCR7, increased significantly (all P
0.05) (Figure 3, top). For quantitative assessment of T-cell responses, T-cell antigen receptor (TCR)-, IFN-–, and CD40L-specific sequences were measured (Figure 3, bottom). Control constructs, including constructs without DCs and those populated with DCs but not cocultured with CD4 T cells, lacked detectable transcripts for TCR, IFN-, and CD40L. In DC-populated arterial walls exposed to CD4 T cells but not to TLR4 ligand, a low number of T cells accumulated and produced minute amounts of IFN- and CD40L. In contrast, TLR4 triggering had profound effects on autologous DC–CD4 T-cell interaction in the 3D wall space. T-cell accumulation doubled (P=0.004); IFN- (P=0.03) and CD40L (P=0.002) transcription increased markedly, demonstrating successful T-cell activation. Notably, these T cells derived from the same donor as the DCs, thus displaying autoimmunity. Coculturing of autologous T cells and DCs at ratios similar to those reached in the bioartificial arteries does not induce T-cell activation (data not shown). Thus, the 3D configuration of the vessel wall appears to optimize interactions between DCs and T cells, and sensing of TLR4 ligands is sufficient to induce productive priming of autologous T cells, breaking self-tolerance and mediating autoreactivity.
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With TLR4 stimulation sufficient to initiate adaptive immunity, it was important to examine whether this process supported chronic inflammation of the vascular structure. Vascular inflammation is characterized by T-cell invasion deep into the wall layers. Cross-sectioning of the constructs allowed for measuring the depth of cell infiltration into the VSMC layer. Analysis of T-cell infiltrates in DC-populated, LPS-activated tubular constructs revealed that T cells invaded deeply into the VSMC layer. Infiltrating T cells clustered and were associated with extensive matrix damage (Figure 4C), suggesting selective development of T-cell effector functions. Through digital image analysis, the infiltration depth for each cell was determined. As shown in Figure 4B, both CD11c immature and CD83+ mature DC populations were stationary at the outer edge and failed to migrate centrally. In contrast, the LPS trigger was highly effective in allowing CD4 T cells to penetrate through the wall, reaching deep into the VSMC layer (Figure 4D) (P<0.05). Media invasion was significantly less efficient in constructs that lacked DCs, assigning a critical position to DCs in regulating the mobility of CD4 T cells. Thus, DCs positioned at the media–adventitia border recruit and activate CD4 T cells and instruct them to invade into the wall structure.
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Innate Immune Cells Display a Hierarchy of Pathogen Sensing and T-Cell Stimulatory Capacity in the Vascular Wall
Vessel wall inflammatory infiltrates typically contain distinct populations of innate immune cells, all of which have been suspected to have APC and T-cell stimulatory functions. To compare monocytes, macrophages, and DCs for these critical proinflammatory actions, we engineered tubular constructs and reconstituted them with purified CD14+ monocytes, in vitro–generated macrophages, or in vitro–generated DCs. All cell populations derived from the identical donor, and sections from the same bioconstruct were used in each experiment. To probe T-cell–activating capacities, autologous CD4 T cells were added to the reconstituted constructs after pretreatment with either LPS or medium. Functional activities of the 3 different APC populations when integrated into the tubular constructs are summarized in Figure 5. CD83 induction only occurred in constructs harboring DCs, with a marked effect of LPS in upregulating this molecule. CD86 induction was strongest in DC-reconstituted constructs but was induced in macrophage-containing vessels. None of the conditions was associated with significant upregulation of the monocyte and macrophage activation markers CD11b and CD163. Both of these markers appeared in high abundance when monocytes and macrophages were stimulated with LPS in tissue culture (data not shown). DC-reconstituted constructs were most effective in recruiting T cells and inducing CD40L, a highly sensitive indicator of in situ T-cell activation. Macrophages embedded in the vascular tubes were able to attract T cells but were not able to upregulate CD40L, probably resulting from only borderline expression of CD86 (Figure 5). Monocytes failed to respond to the LPS trigger, remained negative for CD83 and CD86, and reacted with minimal increases in CD11b and CD163 transcription. Monocyte-supplemented constructs lacked T-cell infiltrates and signs of T-cell activation. Neither preactivation of monocytes before embedding them into the wall nor preactivation of the VSMC layer (data not shown) could provide conditions permissive for monocyte-mediated T-cell recruitment and activation. In essence, monocytes failed to sense LPS effectively when positioned in the unique microenvironment of the vessel wall and could not function as APCs. Macrophages exhibited minor T-cell–activating capacity. DCs emerged as superior sensors of pathogen-derived motifs and inducers of adaptive immune responses.
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DCs Outperform Other APCs in Multilayered Arterial Constructs
The tubular constructs used as an experimental system in the above studies were engineered from collagen matrix and human VSMCs. To assemble constructs that more closely mimic the wall of human medium-sized arteries, we developed a system that allowed us to build multilayered tubes. VSMC constructs were closed on both ends with Luer stoppers, and HUVECs were injected into the lumen (Figure 6A). Within 24 hours, the endothelial cells attached to the luminal surface and formed an endothelial monolayer (Figure 6B). To explore whether the presence of endothelial cells affected pathogen-sensing and immunostimulatory capacities of different APC populations, such intimal–medial tubular constructs were reconstituted with monocytes, macrophages, and DCs as described above. The hierarchy of APCs was unchanged by the presence of the endothelial layer.
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Discussion |
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This study examined mechanisms of vascular inflammation using a novel model of 3D tissue-engineered vessels mimicking the space arrangements of human medium-sized arteries. Wall-embedded APCs display a hierarchy of inflammation-promoting capacity. DCs resembling the population of indigenous vascular DCs present in such vessels are highly efficient in sensing bacterial products and facilitating T-cell recruitment, in situ activation, and invasiveness into the VSMC layer. In essence, DC–T-cell interactions in this unique microspace break T-cell tolerance and induce tissue-damaging immune responses. In contrast, macrophages have only limited antigen-presenting functions, and monocytes fail to attract and activate T cells.
In our previous studies of medium-sized– and large-vessel vasculitis, the adventitia has emerged as a critical site of immune recognition and regulation.1,9,11 VSMC injury, fragmentation of elastic membranes, and intimal hyperproliferation are mostly mediated though effector macrophages,19–22 but these macrophages are ultimately controlled though adventitial IFN-–producing T cells.19–22,27,28 The adventitia is also critically involved in atherosclerosis.29,30 Swine exposed to atheroma-inducing conditions remodel the adventitial vasa vasorum network before forming fatty streaks.31 Dense adventitial infiltrates of T cells, macrophages, and mast cells consistently accompany plaque inflammation.30 These data highlight the functional importance of exterior wall regions, even for pathologies primarily unfolding in the subendothelial space. In giant cell vasculitis, the outer vessel wall influences disease processes principally through DCs placed at the media–adventitia border.1,9 In SCID chimeras implanted with human temporal arteries, LPS injection followed by the adoptive transfer of T cells is sufficient to initiate wall inflammation.9
The present study attempted to recapitulate immune recognition events in the unique microspace of the vessel, with particular emphasis on spatial arrangements. Interestingly, exogenous DCs settled in the most peripheral VSMC layer, a position that closely resembles their physiologic positioning. DCs are a rare but effective cell population that specialize in engulfing and processing antigens and presenting them to T lymphocytes.6 Their main function lies in screening the microenvironment for tissue injury and infection. Besides priming T-cell responses, they also control peripheral tolerance and prevent autoimmunity.8 DCs express a repertoire of receptors to recognize macromolecules derived from different types of microorganisms, including Gram-positive and Gram-negative bacteria, fungi, protozoa, and viruses.32 Why they are placed in the arterial wall is not clear, because their presence increases the risk of inflammation with collateral vascular damage. Given the nature of blood vessels, such immune responses could cause fatal consequences and need to be avoided. Accordingly, it has been proposed that vascular DCs are primarily tolerogenic, creating an immunoprivilege for the artery.1
Direct effects of the microenvironment on the capability of APCs to activate T cells were suggested by divergent functions of DCs, macrophages, and monocytes. None of the experimental conditions provided conditions in which monocytes initiated adaptive immune responses. From the data obtained in the present experimental system, monocytes do not appear to participate in the earliest steps of vessel wall inflammation. If monocytes were matured into macrophages, LPS-sensing and limited T-cell activation could be achieved but far less efficiently than by DCs. Increasing LPS doses or numbers of wall-embedded macrophages could not compensate for the lack of efficiency in APC function. Monocytic phagocytes are central players in the early and late stages of atherosclerosis and are critical effector cells in the granulomatous lesions of vasculitis. However, freshly arrived monocytes can obviously not drive vascular inflammation and even matured macrophages are inferior APCs. Possibly, the divergent functions of DCs, monocytes, and macrophages result from complex interactions with other cell populations, such as endothelial cells. However, in bioartificial arteries engineered to have an endothelial layer covering the macrolumen, monocytes and macrophages continued to fail in providing APC functions comparable to those of DCs. Thus, when analyzing early steps in vessel wall inflammation, DCs have a unique position. Monocytes and macrophages appear to be committed to functional pathways that do not include CD4 T-cell priming/stimulation. We made the interesting observation that the endothelial layer could enhance the overall strength of immune activation for both macrophages and DCs (Figures 5 and 6
), suggesting as yet unknown, distal effects of endothelial cells.
Autologous CD4 T cells recruited to the bioartificial arteries by LPS-triggered DCs entered the activation cycle typically initiated by antigen contact. Only autoantigens were available in the system, indicating breakdown of self-tolerance. Altered-self antigens are suspected to drive inflammation in atherosclerosis and are targeted through novel vaccine strategies.33 In the bioartificial arteries, T cells evolved into tissue-invasive effector cells, penetrating deeply into the medial layer. Transcription of IFN- pointed toward T-cell differentiation into TH1 type helper T cells. This effector function is typical for T cells that maintain arterial wall inflammation.9
Loss of T-cell tolerance in this model of vascular inflammation required stimulation of DCs through TLR ligands, demonstrating that microbe-derived products facilitate and/or enhance immune recognition in the vasculature. Indeed, a positive link between infectious agents and atherosclerosis has been established.34 Circulating LPS would suffice to threaten the integrity of medium-sized and large arteries, which are prone to develop complicated and inflamed atherosclerotic lesions.35
The importance of the size and dimensions of human arteries has been considered in studies addressing atherosclerosis disease models. Voisard et al have created a 3D human coronary in vitro model by culturing human endothelial cells and VSMCs on both sides of a porous filter.36 In this model, monocytes and T cells interacted with endothelial cells and VSMCs, inducing myofibroblast proliferation. Other components of vascular function include the close relationship between shear stress and the wall as well as the impact of cyclic pulsations on wall-residing cell populations. The current study suggests that DC migration patterns also depend on surrounding cell populations. Three-dimensional tubular construct seeding led to positioning of the DCs in the external VSMC layer, avoiding random migration through the VSMC layer. The data presented here favor reciprocity in the interactions between DCs and T cells in the vessel wall, with a remarkably small number of DCs having profound immunoregulatory function. T cells clearly respond to DC encounter by invading deeply into the wall. Contact duration and kinetics of T cells communicating with APCs in a 3D environment can vary considerably. Cytoskeletal activity of the APCs seems to be 1 parameter that modulates outcomes of T-cell priming. Further studies are necessary to identify the unique signals provided to T cells as they enter the VSMC layer and cooperate with local DCs.
In summary, bioartificial arteries built to the specifications of human medium-sized arteries, such as carotid, subclavian, renal, mesenteric, and coronary arteries, are infiltrated by CD4 T cells after DCs embedded in the wall receive activating signals from TLR4 ligands. DCs in the outermost VSMC layer clearly have gatekeeper function in attracting, retaining, and stimulating autoreactive CD4 T cells. DC and T-cell functions are optimized as these 2 populations meet in the 3D space of a vascular tube, assigning modulatory function not only to vessel wall-residing cells but also to the 3D environment. Blood vessels, by virtue of their structure and dimensions, emerge as immunocompetent organs that are at risk to host-autoreactive inflammatory responses.
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Acknowledgments |
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We thank Sergey Pryshchep, PhD, for help with preparing the figures and Tamela Yeargin for manuscript editing.
Sources of Funding
This work was funded in part by NIH grants RO1 AI 44142, RO1 EY 11916, RO1 HL 63919, and RO1 AI 57266. K.S. was supported by a grant from the Mochida Memorial Foundation for Medical Research (Tokyo, Japan).
Disclosures
None.
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Footnotes |
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*Both authors contributed equally to this work.
Original received August 9, 2007; revision received December 5, 2007; accepted January 7, 2008.
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