Influence of extracellular matrix proteins on the development of cultured human dendritic cells

Matrix-Bound Hyaluronan Molecular Weight as a Regulator of Dendritic Cell Immune Potency

Hyaluronic acid (HA) is a glycosaminoglycan in the extracellular matrix with immunoregulatory properties depending on its molecular weight (MW). However, the impact of matrix-bound HA on dendritic cells (DCs) remains unclear due to varying distribution of HA MW under different physiological conditions. To investigate DCs in defined biosystems, 3D collagen matrices modified with HA of specific MW with similar microstructure and HA levels are used. It is found that HA MW influences cytokine binding to matrix, suggesting modulation of cytokine availability by the different HA MWs. These studies on DC immune potency reveal that low MW HA (8-15 kDa) enhances immature DC differentiation and antigen uptake, while medium (MMW-HA; 500-750 kDa) and high MW HA (HMW-HA; 1250-1500 kDa) increase cytokine secretion in mature DCs. The effect on DC phenotype and cytokine secretion by different MWs of HA is independent of CD44. However, blocking the CD44 receptor reveals its potential role in regulating acute inflammation through increased secretion of CCL2, CXCL8, and IL-6. Additionally, MMW- and HMW-HA matrices reduce migratory capacity of DCs, dependent on CD44. Overall, these findings provide insights into MW-dependent effects of matrix-bound HA on DCs, opening avenues for the design of DC-modulating materials to enhance DC-based therapy.

Radiotherapy-induced tumor physical microenvironment remodeling to overcome immunotherapy resistance

The clinical benefits of immunotherapy are proven in many cancers, but a significant number of patients do not respond well to immunotherapy. The tumor physical microenvironment (TpME) has recently been shown to affect the growth, metastasis and treatment of solid tumors. The tumor microenvironment (TME) has unique physical hallmarks: 1) unique tissue microarchitecture, 2) increased stiffness, 3) elevated solid stress, and 4) elevated interstitial fluid pressure (IFP), which contribute to tumor progression and immunotherapy resistance in a variety of ways. Radiotherapy, a traditional and powerful treatment, can remodel the matrix and blood flow associated with the tumor to improve the response rate of immune checkpoint inhibitors (ICIs) to a certain extent. Herein, we first review the recent research advances on the physical properties of the TME and then explain how TpME is involved in immunotherapy resistance. Finally, we discuss how radiotherapy can remodel TpME to overcome immunotherapy resistance.

The role of dendritic cells in the immunomodulation to implanted biomaterials

Considering the substantial role played by dendritic cells (DCs) in the immune system to bridge innate and adaptive immunity, studies on DC-mediated immunity toward biomaterials principally center on their adjuvant effects in facilitating the adaptive immunity of codelivered antigens. However, the effect of the intrinsic properties of biomaterials on dendritic cells has not been clarified. Recently, researchers have begun to investigate and found that biomaterials that are nonadjuvant could also regulate the immune function of DCs and thus affect subsequent tissue regeneration. In the case of proteins adsorbed onto biomaterial surfaces, their intrinsic properties can direct their orientation and conformation, forming “biomaterial-associated molecular patterns (BAMPs)”. Thus, in this review, we focused on the intrinsic physiochemical properties of biomaterials in the absence of antigens that affect DC immune function and summarized the underlying signaling pathways. Moreover, we preliminarily clarified the specific composition of BAMPs and the interplay between some key molecules and DCs, such as heat shock proteins (HSPs) and high mobility group box 1 (HMGB1). This review provides a new direction for future biomaterial design, through which modulation of host immune responses is applicable to tissue engineering and immunotherapy.

Fibromodulin Ablation Exacerbates the Severity of Acute Colitis

Introduction

Epidemiological studies have associated pigment production with protection against certain human diseases. In contrast to African Americans, European descendants are more likely to suffer from angiogenesis-dependent and inflammatory diseases, such as wet age-related macular degeneration (ARMD) and ulcerative colitis (UC), respectively.

Methods

In a mouse model of dextran sulfate sodium (DSS)-induced acute colitis, the effect of fibromodulin (FMOD) depletion was examined on colitis severity.

Results

In this study, albino mice that produce high levels of FMOD developed less severe acute colitis compared with mice lacking in FMOD as assessed by clinical symptoms and histopathological changes. FMOD depletion affected the expression of tight junction proteins, contributing to the destruction of the epithelial barrier. Furthermore, this study revealed a stronger inflammatory response after DSS treatment in the absence of FMOD, where FMOD depletion led to an increase in activated T cells, plasmacytoid dendritic cells (pDCs), and type I interferon (IFN) production.

Discussion

These findings point to FMOD as a potential biomarker of disease severity in UC among light-skinned individuals of European descent.

Toward a Better Regeneration through Implant-Mediated Immunomodulation: Harnessing the Immune Responses

Tissue repair/regeneration, after implantation or injury, involves comprehensive physiological processes wherein immune responses play a crucial role to enable tissue restoration, amidst the immune cells early-stage response to tissue damages. These cells break down extracellular matrix, clear debris, and secret cytokines to orchestrate regeneration. However, the immune response can also lead to abnormal tissue healing or scar formation if not well directed. This review first introduces the general immune response post injury, with focus on the major immune cells including neutrophils, macrophages, and T cells. Next, a variety of implant-mediated immunomodulation strategies to regulate immune response through physical, chemical, and biological cues are discussed. At last, various scaffold-facilitated regenerations of different tissue types, such as, bone, cartilage, blood vessel, and nerve system, by harnessing the immunomodulation are presented. Therefore, the most recent data in biomaterials and immunomodulation is presented here in a bid to shape expert perspectives, inspire researchers to go in new directions, and drive development of future strategies focusing on targeted, sequential, and dynamic immunomodulation elicited by implants.

Dendritic Cells as Targets for Biomaterial-Based Immunomodulation

Various subtypes of immunocytes react against implanted biomaterials to eliminate the foreign body object from the host's body. Among these cells, dendritic cells (DCs) play a key role in early immune response, later engaging lymphocytes through antigens presentation. Due to their capability to induce tolerogenic or immunogenic responses, DCs have been considered as key therapeutic targets for immunomodulatory products. For instance, tolerogenic DCs are applied in the treatment of autoimmune diseases, rejection of allograft transplantation, and implanted biomaterial. Due to the emerging importance of DCs in immunomodulatory biomaterials, this Review summarizes DCs' responses-such as adhesion, migration, and maturation-to biomaterials. We also review some examples of key molecules and their applications in DCs' immunoengineering. These evaluations would pave the way for designing advanced biomaterials and nanomaterials to modulate the immune system, applicable in tissue engineering, transplantation, and drug delivery technologies.

Effect of laminin environments and tumor factors on the biology of myeloid dendritic cells

Dendritic cells (DCs) are immune cells that surveil the organism for infections or malignancies and activate specific T lymphocytes initiating specific immune responses. Contrariwise, DCs have been show to participate in the development of diseases, among them some types of cancer by inducing angiogenesis or immunosuppression. The ultimate fate of DC functions regarding their role in disease or health is prompted by signals from the microenvironment. We have previously shown that the interaction of DCs with various extracellular matrix components modifies the immune properties and angiogenic potential of these cells. The objective of the current studies was to investigate the angiogenic and immune profile of murine myeloid DCs upon interaction with laminin environments, with a particular emphasis on ovarian cancer. Our results show that murine ovarian tumors produce several types of laminins, as determined by PCR analysis, and also that tumor-associated DCs, both from ascites or solid tumors express adhesion molecules capable of interacting with these molecules as determined by flow cytometry and PCR analysis. Further, we established that DCs cultured on laminin upregulate both AKT and MEK signaling pathways, and that long-term culture on laminin surfaces decreases the immunological capacities of these cells when compared to the same cells cultured on synthetic substrates. In addition, we observed that tumor conditioned media was able to modify the metabolic status of these cells, and also reprogram the development of DCs from bone marrow precursors towards the generation of myeloid-derived suppressor cells. Overall, these studies demonstrate that the interaction between soluble factors and extracellular matrix components of the ovarian cancer microenvironment shape the biology of DCs and thus help them become co-conspirators of tumor growth.

Expression of Plet1 controls interstitial migration of murine small intestinal dendritic cells

Under homeostatic conditions, dendritic cells (DCs) continuously patrol the intestinal lamina propria. Upon antigen encounter, DCs initiate C‐C motif chemokine receptor 7 (CCR7) expression and migrate into lymph nodes to direct T cell activation and differentiation. The mechanistic underpinnings of DC migration from the tissues to lymph nodes have been largely elucidated, contributing greatly to our understanding of DC functionality and intestinal immunity. In contrast, the molecular mechanisms allowing DCs to efficiently migrate through the complex extracellular matrix of the intestinal lamina propria prior to antigen encounter are still incompletely understood. Here we show that small intestinal murine CD11b⁺CD103⁺ DCs express Placenta‐expressed transcript 1 (Plet1), a glycophoshatidylinositol (GPI)‐anchored surface protein involved in migration of keratinocytes during wound healing. In the absence of Plet1, CD11b⁺CD103⁺ DCs display aberrant migratory behavior, and accumulate in the small intestine, independent of CCR7 responsiveness. RNA‐sequencing indicated involvement of Plet1 in extracellular matrix‐interactiveness, and subsequent in‐vitro migration assays revealed that Plet1 augments the ability of DCs to migrate through extracellular matrix containing environments. In conclusion, our findings reveal that expression of Plet1 facilitates homeostatic interstitial migration of small intestinal DCs.

OSCAR-collagen signaling in monocytes plays a proinflammatory role and may contribute to the pathogenesis of rheumatoid arthritis

Osteoclast-associated receptor (OSCAR) is an activating receptor expressed by human myeloid cells. Collagen type I (ColI) and collagen type II (ColII) serve as ligands for OSCAR. OSCAR-collagen interaction stimulates RANK-dependent osteoclastogenesis. We have recently reported that OSCAR promotes functional maturation of monocyte-derived dendritic cells. OSCAR is upregulated on monocytes from rheumatoid arthritis (RA) patients with active disease, and these monocytes show an increased proosteoclastogenic potential. In the current study, we have addressed a functional role for an OSCAR-collagen interaction on monocytes. We show that OSCAR-ColII signaling promoted the survival of monocytes. Moreover, ColII stimulated the release of proinflammatory cytokines by monocytes from healthy donors, which could be completely blocked by an anti-OSCAR monoclonal antibody. Mononuclear cells from the synovial fluid of RA patients plated on ColII secreted TNF-α and IL-8 in an OSCAR-dependent manner. Global RNA profiling showed that components of multiple signaling pathways relevant to RA pathogenesis are regulated at the transcriptional level by OSCAR in monocytes. Thus, OSCAR can play a proinflammatory role in monocyte-derived cells and may contribute crucially on multiple levels to RA pathogenesis.

Collagen I-induced dendritic cells activation is regulated by TNF-alpha production through down-regulation of IRF4

Previously we have shown that collagen I enhances the maturation and function of dendritic cells (DCs). Inflammatory mediators such as tumour necrosis factor (TNF)- alpha, interleukin (IL)-1 beta and lipopolysaccharide (LPS) are also known to activate DCs. Here we investigated the involvement of TNF-alpha on the collagen I-induced DCs activation. TNF-a neutralization inhibited collagen I-induced IL-12 secretions by DCs. Additionally, we observed suppression of collagen I-induced costimulatory molecules expression along with down-regulation of genes involved in DCs activation pathway. Furthermore, TNF- alpha inhibition upon collagen Istimulation up-regulated the expression of interferon regulatory transcription factor IRF4, when compared to collagen I only treated cells. Collectively, our data demonstrate that collagen I induce TNF- alpha production, which is crucial for the activation and function of DCs, through down-regulation of IRF4, and implicates the importance in development of anti- TNF-alpha therapeutics for several inflammatory diseases.

Collagen induces maturation of human monocyte-derived dendritic cells by signaling through osteoclast-associated receptor

Osteoclast-associated receptor (OSCAR) is widely expressed on human myeloid cells. Collagen types (Col)I, II, and III have been described as OSCAR ligands, and ColII peptides can induce costimulatory signaling in receptor activator for NF-κB-dependent osteoclastogenesis. In this study, we isolated collagen as an OSCAR-interacting protein from the membranes of murine osteoblasts. We have investigated a functional outcome of the OSCAR-collagen interaction in human monocyte-derived dendritic cells (DCs). OSCAR engagement by ColI/II-induced activation/maturation of DCs is characterized by upregulation of cell surface markers and secretion of cytokines. These collagen-matured DCs (Col-DCs) were efficient drivers of allogeneic and autologous naive T cell proliferation. The T cells expanded by Col-DCs secreted cytokines with no clear T cell polarization pattern. Global RNA profiling revealed that multiple proinflammatory mediators, including cytokines and cytokine receptors, components of the stable immune synapse (namely CD40, CD86, CD80, and ICAM-1), as well as components of TNF and TLR signaling, are transcriptional targets of OSCAR in DCs. Our findings indicate the existence of a novel pathway by which extracellular matrix proteins locally drive maturation of DCs during inflammatory conditions, for example, within synovial tissue of rheumatoid arthritis patients, where collagens become exposed during tissue remodeling and are thus accessible for interaction with infiltrating precursors of DCs.

Dendritic cells: In vitro culture in two- and three-dimensional collagen systems and expression of collagen receptors in tumors and atherosclerotic microenvironments

Dendritic cells (DCs) are immune cells found in the peripheral tissues where they sample the organism for infections or malignancies. There they take up antigens and migrate towards immunological organs to contact and activate T lymphocytes that specifically recognize the antigen presented by these antigen presenting cells. In the steady state there are several types of resident DCs present in various different organs. For example, in the mouse, splenic DC populations characterized by the co-expression of CD11c and CD8 surface markers are specialized in cross-presentation to CD8 T cells, while CD11c/SIRP-1α DCs seem to be dedicated to activating CD4 T cells. On the other hand, DCs have also been associated with the development of various diseases such as cancer, atherosclerosis, or inflammatory conditions. In such disease, DCs can participate by inducing angiogenesis or immunosuppression (tumors), promoting autoimmune responses, or exacerbating inflammation (atherosclerosis). This change in DC biology can be prompted by signals in the microenvironment. We have previously shown that the interaction of DCs with various extracellular matrix components modifies the immune properties and angiogenic potential of these cells. Building on those studies, herewith we analyzed the angiogenic profile of murine myeloid DCs upon interaction with 2D and 3D type-I collagen environments. As determined by PCR array technology and quantitative PCR analysis we observed that interaction with these collagen environments induced the expression of particular angiogenic molecules. In addition, DCs cultured on collagen environments specifically upregulated the expression of CXCL-1 and -2 chemokines. We were also able to establish DC cultures on type-IV collagen environments, a collagen type expressed in pathological conditions such as atherosclerosis. When we examined DC populations in atherosclerotic veins of Apolipoprotein E deficient mice we observed that they expressed adhesion molecules capable of interacting with collagen. Finally, to further investigate the interaction of DCs with collagen in other pathological conditions, we determined that both murine ovarian and breast cancer cells express several collagen molecules that can contribute to shape their particular tumor microenvironment. Consistently, tumor-associated DCs were shown to express adhesion molecules capable of interacting with collagen molecules as determined by flow cytometry analysis. Of particular relevance, tumor-associated DCs expressed high levels of CD305/LAIR-1, an immunosuppressive receptor. This suggests that signaling through this molecule upon interaction with collagen produced by tumor cells might help define the poorly immunogenic status of these cells in the tumor microenvironment. Overall, these studies demonstrate that through interaction with collagen proteins, DCs can be capable of modifying the microenvironments of inflammatory disease such as cancer or atherosclerosis.

Absence of immune responses with xenogeneic collagen and elastin

Novel tissue-engineering approaches for cardiovascular matrices based on xenogeneic extracellular matrix protein (ECMp) constituents require a detailed evaluation of their interaction with essential immune cell subsets playing a role in innate or adaptive immunity. Therefore, in this study, the effects of xenogeneic (porcine, bovine) collagen type I and elastin as the two main components of the heart valve ECM were analyzed in comparison to their human equivalents. First, their potential to induce maturation and cytokine secretion of human dendritic cells (DC) was tested by flow cytometry. Second, the influence on proliferation and cytokine release of purified human B and T cells was measured. We could demonstrate that xenogeneic collagen type I and elastin are not able to trigger the maturation of DC as verified by the lack of CD83 induction accompanied by a low tumor necrosis factor-α release. Moreover, both ECMp showed no effect on the proliferation and the interleukin-6 release of either unstimulated or prestimulated B cells. Additionally, anti-CD3-induced purified T cell proliferation and secretion of cytokines was not affected. All in vitro data verify the low immunogenicity of porcine and bovine collagen type I and elastin and favor their suitability for tissue-engineered scaffolds.

Astrocytes inhibit microglial surface expression of dendritic cell-related co-stimulatory molecules through a contact-mediated process

Murine microglia cultured in isolation were treated sequentially with granulocyte/monocyte colony-stimulating factor (GM-CSF) (5 days) and lipopolysaccharide (LPS) (2 days) to elicit a mature dendritic cell-like (DC-like) phenotype. Examined by flow cytometry microglia thus isolated show high surface expression of CD11c together with the co-stimulatory molecules CD40, CD80, and CD86 that are necessary for T-cell activation. In contrast, microglia co-cultured with astrocytes fail to achieve a mature DC-like phenotype. Contact with the astrocytic environment is necessary for the inhibition. Failure was not because of a more rapid degradation of protein. Bone marrow-derived cells, like microglia, were prevented by astrocytes from attaining a mature DC phenotype. Although GM-CSF pre-treatment substantially increases mRNA of co-stimulatory molecules and major histocompatibility complex (MHC) Class II in isolated microglia, co-cultured microglia await treatment with LPS to up-regulate them. In contrast, western blot and immunocytochemical analysis revealed that it is not a failure of transcription or translation, nor is it a more rapid degradation of mRNA that is responsible for the low surface expression; rather microglia co-cultured with astrocytes produce mRNA and protein but do not traffic the protein onto the cell surface.

Immune responses to implants - a review of the implications for the design of immunomodulatory biomaterials

A key for long-term survival and function of biomaterials is that they do not elicit a detrimental immune response. As biomaterials can have profound impacts on the host immune response the concept emerged to design biomaterials that are able to trigger desired immunological outcomes and thus support the healing process. However, engineering such biomaterials requires an in-depth understanding of the host inflammatory and wound healing response to implanted materials. One focus of this review is to outline the up-to-date knowledge on immune responses to biomaterials. Understanding the complex interactions of host response and material implants reveals the need for and also the potential of "immunomodulating" biomaterials. Based on this knowledge, we discuss strategies of triggering appropriate immune responses by functional biomaterials and highlight recent approaches of biomaterials that mimic the physiological extracellular matrix and modify cellular immune responses.

The interplay between surfaces and soluble factors define the immunologic and angiogenic properties of myeloid dendritic cells

BACKGROUND

Dendritic cells (DCs) are antigen presenting cells capable of inducing specific immune responses against microbial infections, transplant antigens, or tumors. Interestingly, microenvironment conditions such as those present in tumor settings might induce a DC phenotype that is poorly immunogenic and with the capability of promoting angiogenesis. We hypothesize that this plasticity may be caused not only by the action of specific cytokines or growth factors but also by the properties of the surfaces with which they interact, such as extracellular matrix (ECM) components.

RESULTS

Herewith we studied the effect of different surfaces and soluble factors on the biology of DCs. To accomplish this, we cultured murine myeloid(m) DCs on surfaces coated with fibronectin, collagen I, gelatin, and Matrigel using poly-D-lysine and polystyrene as non-biological surfaces. Further, we cultured these cells in the presence of regular DC medium (RPMI 10% FBS) or commercially available endothelial medium (EGM-2). We determined that mDCs could be kept in culture up to 3 weeks in these conditions, but only in the presence of GM-CSF. We were able to determine that long-term DC cultures produce an array of angiogenic factors, and that some of these cultures still retain the capability to induce T cell responses.

CONCLUSIONS

Altogether these data indicate that in order to design DC-based vaccines or treatments focused on changing the phenotype of DCs associated with diseases such as cancer or atherosclerosis, it becomes necessary to fully investigate the microenvironment in which these cells are present or will be delivered.

Persistent activation of dendritic cells after resolution of allergic airway inflammation breaks tolerance to inhaled allergens in mice

RATIONALE

Polysensitization of patients who are allergic is a common feature. The underlying immunologic mechanism is not clear. The maturation status of dendritic cells (DCs) is considered to be important for priming naive T cells in the draining lymph nodes. We hypothesized that chronic airway inflammation can induce an enhanced maturation of airway DCs and facilitate subsequent priming to neoallergens.

OBJECTIVES

To investigate whether chronic airway inflammation could induce an altered activation of airway DCs in mice and whether this influences the development of allergic sensitization.

METHODS

Balb/c mice were repeatedly challenged with DCs to induce a chronic airway inflammation. We evaluated (1) the induction of the main characteristic features of human asthma including persistent remodeling, (2) the maturation status of airway DCs 1 month after inflammation resolved, (3) whether this influences tolerance to inhaled neoallergen, and (4) what type of T helper response would be induced by DCs.

MEASUREMENTS AND MAIN RESULTS

Airway DCs displayed a mature phenotype after complete resolution of airway eosinophilia. Inhalation of a neoallergen without any adjuvant was able to induce airway inflammation in postinflammation lungs but not in control lungs. One month after inflammation, airway DCs were able to induce Th2 polarization in naive T cells consistent with the up-regulation of the Th2 skewing molecules Ym1/2 and OX-40L compared with DCs of control airways.

CONCLUSIONS

This study provides evidence that sustained maturation of DCs after resolution of Th2-mediated inflammation can contribute to polysensitization.

Adhesive substrates modulate the activation and stimulatory capacity of non-obese diabetic mouse-derived dendritic cells

It is known that adsorbed adhesive proteins on implanted biomaterials modulate inflammatory responses; however, modulation of dendritic cell (DC) responses upon interaction with adhesive proteins has only begun to be characterized. DCs are specialized antigen-presenting cells that modulate both innate and adaptive immune responses. Previously we have shown that the activation and stimulatory capacity of DCs derived from C57BL6/j mice is differentially modulated by adhesive substrates. Here we extend our investigation of adhesive substrate modulation of DC responses to consider the case where the DCs had maturational defects associated with diabetes. Understanding the adhesive responses of DCs in diabetics is potentially important for immunotherapy and tissue engineering applications. In this work we use the non-obese diabetic (NOD) mouse, an established animal model for type 1 diabetes, to generate DCs (NOD-DCs). We demonstrate that NOD-DCs cultured on different adhesive substrates (collagen, fibrinogen, fibronectin, laminin, vitronectin, albumin and serum) respond with substrate-dependent modulation of the surface expression of the stimulatory molecule MHC-II and the co-stimulatory molecules CD80 and CD86 and production of the cytokines IL-12p40 and IL-10. Furthermore, the capacity of NOD-DCs to stimulate CD4(+) T-cell proliferation and cytokine production (IL-4 and IFN-γ) showed substrate-dependent modulation. Specifically, NOD-DCs cultured on vitronectin induced the highest IL-12p40 production, whereas collagen induced the highest IL-10 production. Dendritic cells cultured on collagen, fibrinogen and serum-coated substrates stimulated the highest CD4(+) T-cell proliferation. It was further determined that DCs cultured on vitronectin induced the highest percent population of IL-4-producing T-cells and DCs cultured on a fibronectin-coated substrate induced the highest expression of IFN-γ in T-cells. Pearson's correlation analysis revealed high correlations between T-cell proliferation and DC expression level of CD80 and T-cell production of IL-4 and DC production of IL-10. This demonstration of substrate-based control of NOD-DC activatory and stimulatory capacity, distinct from non-diabetic B6-DC responses, establishes the field of adhesive modulation of immune cell responses and informs the rational design of biomaterials for patients with type 1 diabetes.

Cell culture plastics with immobilized interleukin-4 for monocyte differentiation

Standard cell culture plastic was surface modified by passive adsorption or covalent attachment of interleukin (IL)-4 and investigated for its ability to induce differentiation of human monocytes into mature dendritic cells, a process dose-dependently regulated by IL-4. Covalent attachment of IL-4 proceeded via anthraquinone photochemistry to introduce amine functionalities at the surface followed by coupling of IL-4 through a bifunctional amine-reactive linker. X-ray photoelectron spectroscopy showed that undesirable multilayer formation of the photoactive compound could be avoided by reaction in water instead of phosphate-buffered saline. Passively adsorbed IL-4 was observed to induce differentiation to dendritic cells, but analysis of cell culture supernatants revealed that leakage of IL-4 into solution could account for the differentiation observed. Covalent attachment resulted in bound IL-4 at similar concentrations to the passive adsorption process, as measured by enzyme-linked immunosorbent assays, and the bound IL-4 did not leak into solution to any measurable extent during cell culture. However, covalently bound IL-4 was incapable of inducing monocyte differentiation. This may be caused by IL-4 denaturation or improper epitope presentation induced by the immobilization process, or by biological irresponsiveness of monocytes to IL-4 in immobilized formats.

Macrophage and dendritic cell phenotypic diversity in the context of biomaterials

Macrophages (Mϕ) and dendritic cells (DCs) are critical antigen presenting cells that play pivotal roles in host responses to biomaterial implants. Although Mϕs have been widely studied for their roles in the inflammatory responses against biomaterials, the roles that DCs play in the host responses toward implanted materials have only recently been explored. DCs are of significant research interest because of the emergence of a large number of combination products that cross-traditional medical device boundaries. These products combine biomaterials with biologics, including cells, nucleic acids, and/or proteins. The biomaterial component may evoke an inflammatory response, primarily mediated by neutrophils and Mϕs, whereas the biologic component may elicit an immunogenic immune response, initiated by DCs involving lymphocyte activation. Control of Mϕ phenotypic balance from proinflammatory M1 to reparative M2 is a goal of investigators to optimize the host response to biomaterials. Similarly, control of DC phenotype from proinflammatory to toleragenic is of interest in vaccine delivery and tissue engineering/transplantation situations, respectively. This review discusses the interconnection between innate and adaptive immunity, the comparative and contrasting phenotypes and roles of Mϕs and DCs in immunity, their responses to biomaterials and the strategies to modulate their phenotype for applications in tissue engineering and vaccine delivery. Furthermore, the collaboration between and unique roles of DCs and Mϕs needs to be addressed in future studies to gain a more complete picture of host responses toward combination products.

The role of integrins in the recognition and response of dendritic cells to biomaterials

Biomaterials have the potential to be utilized as immunostimulatory or immunosuppressive delivery agents for biologics. It is hypothesized that this is directed by the ability of a biomaterial to drive dendritic cells (DC) in situ toward an immunostimulatory or an immunosuppressive phenotype, respectively. However, the specific pattern recognition receptors (PRRs) that DCs use to recognize and respond to biomaterials are unknown. From among the many receptors that DCs use to recognize and respond to foreign entities, herein the focus is on integrins. A biomaterial that induces DC maturation, namely poly(lactic-co-glycolic) acid (PLGA), supported increased human monocyte-derived DC adhesion and up-regulation of integrin receptor gene expression, measured via RT-PCR, as compared to culture on tissue culture polystyrene (TCPS). This was not observed for a biomaterial that does not support DC maturation. Through antibody-blocking techniques, the adhesion to both TCPS and PLGA was found to be β(2) integrin dependent and β(1) independent. Significantly, inhibiting β(2)-mediated adhesion to biomaterials via blocking antibodies also lowered the level of maturation of DCs (CD86 expression). β(2) integrins (but not β(1)) were found localized in biomaterial-adherent DC podosomes and also were found in direct contact with the PLGA surface. Therefore, it appeared that β(2) integrin-mediated adhesion is involved in determining the state of DC maturation on the PLGA surface. DC adhesion to biomaterials may be engaged or avoided to manipulate an immune response to biological component delivered with a biomaterial carrier.

Lysophosphatidylcholine-mediated functional inactivation of syndecan-4 results in decreased adhesion and motility of dendritic cells

Following antigen contact, maturation and migration of DCs into lymphatic tissues are crucial to the developing immune response or maintenance of tolerance. Lysophosphatidylcholine (LysoPC) is generated during apoptosis of cells and acts as a "find-and-eat-me" signal thought to prevent autoimmunity. Moreover, LysoPC can activate PKCδ and initiates a signaling cascade that leads to phosphorylation and inactivation of syndecan-4 (SDC4), a heparansulfate proteoglycan integrin co-receptor. In human monocyte-derived DCs, we recently demonstrated that SDC4 is upregulated during maturation thereby stimulating DC motility. Here, we investigate the effects of LysoPC on DC motility as well as on the involvement of PKCδ phosphorylation-dependent regulation of DC motility by SDC4 and PKCα. Employing a static adhesion assay and videomicroscopy, we show that LysoPC inhibits adhesion of DCs to fibronectin and motility of DCs by decreasing podosome formation. Moreover, DC podosome formation and motility, which both are regulated by SDC4 and subject to control by PKCδ-dependent phosphorylation of SDC4, were inhibited in LysoPC-matured DCs. Thus, these DC are defective in adhesion and migration. Based on our results, we hypothesize that LysoPC released during apoptosis might delay DC migration to lymphoid organs and thus prevent autoimmunity.

The modulation of dendritic cell integrin binding and activation by RGD-peptide density gradient substrates

Dendritic cells (DCs) are central regulators of the immune system that operate in both innate and adaptive branches of immunity. Activation of DC by numerous factors, such as danger signals, has been well established. However, modulation of DC functions through adhesion-based cues has only begun to be characterized. In this work, DCs were cultured on surfaces presenting a uniform gradient of the integrin-targeting RGD peptide generated using the recently established "universal gradient substrate for click biofunctionalization" methodology. Surface expression of activation markers (costimulatory molecule CD86 and stimulatory molecule MHC-II) and production of cytokines IL-10 and IL-12p40 of adherent DCs was quantified in situ. Additionally, bound alpha(V) integrin was quantified in situ using a biochemical crosslinking/extraction method. Our findings demonstrate that DCs upregulated CD86, MHC-II, IL-10, IL-12p40 and alpha(V) integrin binding as a function of RGD surface density, with production of IL-12p40 being the marker most sensitive to RGD surface density. Surface expression of activation markers demonstrated moderate correlation with alpha(V) integrin binding, while cytokine production was highly correlated with alpha(V) integrin binding. This work demonstrates the utility of the surface density gradient platform as a high-throughput method to investigate RGD density-dependent DC adhesive responses. Furthermore, this quantitative analysis of DC integrin-based activation represents a first of its type, helping to establish the field of adhesion-based modulation of DCs as a general mechanism that has previously not been defined, and informs the rational design of biomimetic biomaterials for immunomodulation.

Laminin and fibronectin treatment leads to generation of dendritic cells with superior endocytic capacity

Background

Sampling the microenvironment at sites of microbial exposure by dendritic cells (DC) and their subsequent interaction with T cells in the paracortical area of lymph nodes are key events for initiating immune responses. Most of our knowledge of such events in human is based on in vitro studies performed in the absence of extracellular matrix (ECM) proteins. ECM in basement membranes and interstitial spaces of different tissues, including lymphoid organs, plays an important role in controlling specific cellular functions such as migration, intracellular signalling and differentiation. The aim of this study was, therefore, to investigate the impact of two abundant ECM components, fibronectin and laminin, on the phenotypical and functional properties of DC and how that might influence DC induced T-cell differentiation.

Methodology/Principal Findings

Human monocyte derived DC were treated with laminin and fibronectin for up to 48 hours and their morphology and phenotype was analyzed using scanning electron microscopy, flow cytometry and real time PCR. The endocytic ability of DC was determined using flow cytometry. Furthermore, co-culture of DC and T cells were established and T cell proliferation and cytokine profile was measured using H³-thymidine incorporation and ELISA respectively. Finally, we assessed formation of DC-T cell conjugates using different cell trackers and flow cytometry. Our data show that in the presence of ECM, DC maintain a ‘more immature’ phenotype and express higher levels of key endocytic receptors, and as a result become significantly better endocytic cells, but still fully able to mature in response to stimulation as evidenced by their superior ability to induce antigen-specific T cell differentiation.

Conclusion

These studies underline the importance of including ECM components in in vitro studies investigating DC biology and DC-T cell interaction. Within the context of antigen specific DC induced T cell proliferation, inclusion of ECM proteins could lead to development of more sensitive assays.

Adhesive substrate-modulation of adaptive immune responses

While it is well-known that adsorbed proteins on implanted biomaterials modulate inflammatory responses, modulation of dendritic cells (DCs) via adhesion-dependent signaling has only been begun to be characterized. In this work, we demonstrate that adhesive substrates elicit differential DC maturation and adaptive immune responses. We find that adhesive substrates support similar levels of DC adhesion and expression of stimulatory and co-stimulatory molecules. Conversely, DC morphology and differential production of pro- and anti-inflammatory cytokines (IL-12p40 and IL-10, respectively) is adhesive substrate-dependent. For example, DCs cultured on collagen and vitronectin substrates generate higher levels of IL-12p40, whereas DCs cultured on albumin and serum-coated tissue culture-treated substrates produce the higher levels of IL-10 compared to other substrates. Additionally, our results suggest substrate-dependent trends in DC-mediated allogeneic CD4(+) T-cell proliferation and T-helper cell type responses. Specifically, we show that substrate-dependent modulation of DC IL-12p40 cytokine production correlates with CD4(+) T-cell proliferation and T(h)1 type response in terms of IFN-gamma producing T-helper cells. Furthermore, our results suggest substrate-dependent trends in DC-mediated stimulation of IL-4 producing T-cells, but this T(h)2 type response is not dependent on DC production of IL-10 cytokine. This work has impact in the rational design of biomaterials for diverse applications such as tissue-engineered constructs, synthetic particle-based vaccines and the ex vivo culture of DCs for immunotherapies.

IL-12-impaired and IL-12-secreting dendritic cells produce IL-23 upon CD154 restimulation

Experimental studies in monkeys on the basis of ex vivo-generated, reinjected dendritic cells (DCs) allow investigations of primate DC biology in vivo. To study in vitro and in vivo properties of DCs with a reduced capacity to produce IL-12, we adapted findings obtained in vitro with human cells to the rhesus macaque model. Following exposure of immature monocyte-derived monkey DCs to the immunomodulating synthetic polypeptide glatiramer acetate (GA) and to dibutyryl-cAMP (d-cAMP; i.e., a cAMP enhancer that activates DCs but inhibits the induction of Th1 immune responses), the resulting DCs displayed a mature phenotype with enhanced Ag-specific T cell stimulatory function, notably also for memory Th1 cells. Phosphorylation of p38 MAPK was not induced in GA/d-cAMP-activated DCs. Accordingly, these cells secreted significantly less IL-12p40 (p < or = 0.001) than did cytokine-activated cells. However, upon restimulation with rhesus macaque CD154, GA/d-cAMP-activated DCs produced IL-12p40/IL-23. Additionally, DCs activated by proinflammatory cytokines following protocols for the generation of cells used in clinical studies secreted significantly more IL-23 upon CD154 restimulation than following prior activation. Two days after intradermal injection, GA/d-cAMP-activated fluorescence-labeled DCs were detected in the T cell areas of draining lymph nodes. When similarly injected, GA/d-cAMP as well as cytokine-activated protein-loaded DCs induced comparable Th immune responses characterized by secretion of IFN-gamma, TNF, and IL-17, and transiently expanded FOXP3(+) regulatory T cells. Reactivation of primate DCs through CD154 considerably influences their immmunostimulatory properties. This may have a substantial impact on the development of innovative vaccine approaches.

How dying cells alert the immune system to danger

When a cell dies in vivo, the event does not go unnoticed. The host has evolved mechanisms to detect the death of cells and rapidly investigate the nature of their demise. If cell death is a result of natural causes - that is, it is part of normal physiological processes - then there is little threat to the organism. In this situation, little else is done other than to remove the corpse. However, if cells have died as the consequence of some violence or disease, then both defence and repair mechanisms are mobilized in the host. The importance of these processes to host defence and disease pathogenesis has only been appreciated relatively recently. This article reviews our current knowledge of these processes.

The endothelial cell-produced antiangiogenic cytokine vascular endothelial growth inhibitor induces dendritic cell maturation

Angiogenesis is an essential component of chronic inflammation that is linked to carcinogenesis. In this study, we report that human vascular endothelial growth inhibitor (VEGI, TNF superfamily 15), an endothelial cell-produced antiangiogenic cytokine, induces mouse dendritic cell (DC) maturation, a critical event in inflammation-initiated immunity. VEGI-stimulated bone marrow-derived immature DCs display early activation of maturation signaling molecules NF-kappaB, STAT3, p38, and JNK, and cytoskeleton reorganization and dendrite formation. The activation signals are partially inhibited by using a neutralizing Ab against death domain-containing receptor-3 (DR3) or a truncated form of DR3 consisting of the extracellular domain, indicating an involvement of DR3 in the transmission of VEGI activity. A VEGI isoform, TL1A, does not induce similar activities under otherwise identical experimental conditions. Additionally, the cells reveal significantly enhanced expression of mature DC-specific marker CD83, secondary lymphoid tissue-directing chemokine receptor CCR7, the MHC class-II protein (MHC-II), and costimulatory molecules CD40, CD80, and CD86. Functionally, the cells exhibit decreased Ag endocytosis, increased cell surface distribution of MHC-II, and increased secretion of IL-12 and TNF. Moreover, VEGI-stimulated DCs are able to facilitate the differentiation of CD4+ naive T cells in cocultures. These findings suggest that the anticancer activity of VEGI arises from coupling the inhibition of endothelial cell growth with the promotion of the adaptive immune mechanisms through the stimulation of DC maturation.

Discoidin domain receptor 2 is involved in the activation of bone marrow-derived dendritic cells caused by type I collagen

Discoidin domain receptors (DDRs), DDR1 and DDR2, are non-integrin receptor tyrosine kinases for collagen in many cell types. In this study, we investigated the contributions of DDRs to the activation of mouse bone marrow-derived dendritic cells (DCs) by type I collagen (ColI). Our data showed that transcript and protein of DDR2 were expressed constitutively in immature DCs and upregulated in TNF-alpha-stimulated mature DCs. ColI treatment induced DDR2 phosphorylation and subsequently induced the upregulation of IL-12 production, CD86 expression, and antigen uptake activity by immature DCs. Depletion of DDR2 by specific siRNA attenuated significantly an increase in expression of IL-12 and CD86 in ColI-treated DCs. Additionally, DDR2-ColI interaction upregulated the ability of mature DCs to activate allogeneic T cells. These findings suggest that DDR2 is a critical collagen receptor for DC activation and that DDR2-collagen interaction plays an important role in the functional capacity of DCs regulating immune responses.

Monocyte chemoattractant protein-1 (MCP-1) inhibits the intestinal-like differentiation of monocytes

Monocytes (MO) migrating into normal, non-inflamed intestinal mucosa undergo a specific differentiation resulting in a non-reactive, tolerogenic intestinal macrophage (IMAC). Recently we demonstrated the differentiation of MO into an intestinal-like macrophage (MAC) phenotype in vitro in a three-dimensional cell culture model (multi-cellular spheroid or MCS model). In the mucosa of patients with inflammatory bowel disease (IBD) in addition to normal IMAC, a reactive MAC population as well as increased levels of monocyte chemoattractant protein 1 (MCP-1) is found. The aim of this study was to investigate the influence of MCP-1 on the differentiation of MO into IMAC. MCS were generated from adenovirally transfected HT-29 cells overexpressing MCP-1, macrophage inflammatory protein 3 alpha (MIP-3alpha) or non-transfected controls and co-cultured with freshly elutriated blood MO. After 7 days of co-culture MCS were harvested, and expression of the surface antigens CD33 and CD14 as well as the intracellular MAC marker CD68 was determined by flow-cytometry or immunohistochemistry. MCP-1 and MIP-3alpha expression by HT-29 cells in the MCS was increased by transfection at the time of MCS formation. In contrast to MIP-3alpha, MCP-1 overexpression induced a massive migration of MO into the three-dimensional aggregates. Differentiation of IMAC was disturbed in MCP-1-transfected MCS compared to experiments with non-transfected control aggregates, or the MIP-3alpha-transfected MCS, as indicated by high CD14 expression of MO/IMAC cultured inside the MCP-1-transfected MCS, as shown by immunohistochemistry and FACS analysis. Neutralization of MCP-1 was followed by an almost complete absence of monocyte migration into the MCS. MCP-1 induced migration of MO into three-dimensional spheroids generated from HT-29 cells and inhibited intestinal-like differentiation of blood MO into IMAC. It may be speculated that MCP-1 could play a role in the disturbed IMAC differentiation in IBD mucosa.

Chemokines: more than just road signs

Chemokines have long been known to orchestrate dendritic-cell migration in the body. However, recent evidence has shown that chemokines not only direct the trafficking of dendritic cells but also can regulate their maturation status. Here, we propose that this dual function of chemokines ensures that T cells and dendritic cells meet in T-cell regions of lymphoid organs and that antigen is presented in an immunologically optimal context for T-cell priming.

Discoidin domain receptor 1: a new class of receptor regulating leukocyte-collagen interaction

Previous studies demonstrated that type I collagen, a major component of the extracellular matrix, could influence the differentiation and function of leukocytes; however, it is not clear whether those effects of collagen were based on its interaction with the classic collagen receptors, alpha1beta1 and alpha2beta1 integrins. We recently detected significant upregulation of discoidin domain receptor 1 (DDR1), a new class of collagen receptor, in human leukocytes, including neutrophils, monocytes, and lymphocytes, in vitro, leading to the hypothesis that the leukocyte-activating effects of collagen might be owing to its interaction with DDR1. In this review, we summarize our recent findings demonstrating that DDR1-collagen interaction facilitates the adhesion, migration, differentiation/maturation, and cytokine/chemokine production of leukocytes. We also describe the intracellular signaling pathways activated by DDR1 interaction with collagen.

An increased MRP8/14 expression and adhesion, but a decreased migration towards proinflammatory chemokines of type 1 diabetes monocytes

In the early development of type 1 diabetes macrophages and dendritic cells accumulate around the islets of Langerhans at sites of fibronectin expression. It is thought that these macrophages and dendritic cells are derived from blood monocytes. Previously, we showed an increased serum level of MRP8/14 in type 1 diabetes patients that induced healthy monocytes to adhere more strongly to fibronectin (FN). Here we show that MRP8/14 is expressed and produced at a higher level by type 1 diabetes monocytes, particularly after adhesion to FN, creating a positive feedback mechanism for a high fibronectin-adhesive capacity. Also adhesion to endothelial cells was increased in type 1 diabetes monocytes. Despite this increased adhesion the transendothelial migration of monocytes of type 1 diabetes patients was decreased towards the proinflammatory chemokines CCL2 and CCL3. Because non-obese diabetic (NOD) mouse monocytes show a similar defective proinflammatory migration, we argue that an impaired monocyte migration towards proinflammatory chemokines might be a hallmark of autoimmune diabetes. This hampered monocyte response to proinflammatory chemokines questions whether the early macrophage and dendritic cell accumulation in the diabetic pancreas originates from an inflammatory-driven influx of monocytes. We also show that the migration of type 1 diabetes monocytes towards the lymphoid tissue-related CCL19 was increased and correlated with an increased CCR7 surface expression on the monocytes. Because NOD mice show a high expression of these lymphoid tissue-related chemokines in the early pancreas it is more likely that the early macrophage and dendritic cell accumulation in the diabetic pancreas is related to an aberrant high expression of lymphoid tissue-related chemokines in the pancreas.

Direct Effects of Polymyxin B on Human Dendritic Cells Maturation

Polymyxin B is a lipopolysaccharide binding antibiotic used to inactivate potential lipopolysaccharide contaminations when evaluating the activity of different agents on innate immune cells. We report that polymyxin B is able to induce directly in monocyte-derived human dendritic cells (DCs) several functional and molecular modifications characteristic of DCs undergoing a maturation process. DCs incubated with polymyxin B up-regulate the expression of HLA class I and II, the co-stimulatory CD86 molecule, and show an increase in the fraction of adherent cells at short time, which persist at 48 h of incubation. Adhesion to the plate was required for the polymyxin B-induced DCs maturation. A transient activation of IkappaB-alpha/NF-kappaB and ERK1/2 pathways at short time and a further ERK1/2 activation at long term were also detected. Neither up-regulation of the maturation marker CD83 nor activation of p38 nor induction of cytokines secretion was observed in DCs treated with polymyxin B. We demonstrated that inhibition of IkappaB-alpha/NF-kappaB pathway abolishes polymyxin B effects. ERK1/2 inhibition instead allowed DCs treated with polymyxin B to progress in their maturation process as revealed by the increased up-regulation of the CD83 co-stimulatory molecules, the activation of p38, and the reduced adhesion to culture plates at 48 h of incubation. Our results indicate that polymyxin B induces a partial maturation of human DCs through increased adhesion to a substrate and activation of the IkappaB-alpha/NF-kappaB pathway. The increased ERK1/2 activation observed, even though correlating with the initial phases of the maturation process, actually inhibits the occurrence of full maturation.

Maturation of DC is associated with changes in motile characteristics and adherence

Migration of dendritic cells (DC) from sentinel sites to lymphoid tissue entails the initiation and coordination of a complex series of cytoskeletal rearrangements resulting in polarised protrusion, formation of new adhesion points, and detachment. Although many diverse receptor-ligand interactions stimulating DC maturation and migration have been identified, the changes that occur in the structure of the actin cytoskeleton during these processes have received little attention. When derived in vitro, immature DC floated in clumps, and upon addition of maturation stimuli such as lipopolysaccharide (LPS), they rapidly adhered, developed polarity, and assembled actin-rich structures known as podosomes at the leading edge of the cell. Podosome assembly was associated with the specific recruitment of beta2 integrins, which in the absence of the Wiskott Aldrich Syndrome protein (WASp), did not occur. As maturation progressed, normal DC once again became rounded and devoid of podosomes. This change in morphology was closely associated with a quantitatively reduced ability to adhere to fibronectin or ICAM-1-coated surfaces. In immature DC, failure to form podosomes or selective inhibition of the CD18 component of podosomes resulted in a similarly reduced ability to adhere to ICAM-1, indicating that podosomes, through CD18, are necessary for tight adhesion to this ligand. We, therefore, propose that podosomes provide an essential link between directional cell protrusion and achievement of DC translocation by establishing new dynamic anchor points at the front of the cell. The temporal regulation of podosome assembly during DC maturation also suggests that they may be most critical for early movement, perhaps during transmigration of lymphatic endothelium.

Adhesion capacity and integrin expression by dendritic-like cells generated from acute myeloid leukemia blasts by calcium ionophore treatment

OBJECTIVE

Dendritic cells (DC) play a key role in initiation of immune responses. In vitro modified acute myeloid leukemia (AML) blasts acquire certain specific features of DC and are suggested as a potential source of anti-leukemia vaccines. AML-DC have been characterized in terms of costimulatory molecule expression and cytokine production. In contrast, migratory capacity of AML-DC, which is a major attribute of DC required for their in vivo function, remains unknown. Here we present data on adhesion properties and profile of integrin expression of AML-DC.

MATERIALS AND METHODS

Blasts from nine patients were used to generate AML-DC by calcium ionophore treatment. Adhesion of AML-DC to the major components of the extracellular matrix and the profile of integrin expression was studied using flow cytometry.

RESULTS

Similar to their normal counterparts, calcium ionophore-induced AML-DC acquired the ability to bind to fibronectin and in 4 of 7 studied cases to bind to denatured collagen. Adhesion to native collagen remained unchanged during DC-type differentiation of AML blasts. AML-DC and DC obtained from monocytes of healthy donors expressed CD49d, CD49e, alphavbeta3, and alphavbeta5. However, AML-DC from 3 of 8 patients down-regulated CD49d, which plays an important role in cell-to-cell and cell-to-matrix interactions and normally is coexpressed with CD83.

CONCLUSION

The results provide further evidence that AML blasts can be induced to display functional properties characteristic for DC and may prove useful for in vivo delivery and presentation of tumor antigens to the immune system. Abnormal CD49d expression and variability in AML-DC adhesion to denatured collagen indicate that motility of AML-DC from individual patients may vary, and a customized approach is essential for evaluating leukemic cell feasibility for vaccine design.

Activation of Discoidin Domain Receptor 1 Facilitates the Maturation of Human Monocyte-Derived Dendritic Cells Through the TNF Receptor Associated Factor 6/TGF-β-Activated Protein Kinase 1 Binding Protein 1β/p38α Mitogen-Activated Protein Kinase Signaling Cascade

Maturation of dendritic cells (DCs) is critical for their ability to stimulate resting naive T cells in primary immune responses. Previous studies demonstrated that collagen, such as type I collagen, could facilitate DC maturation; however, the basis of collagen-mediated DC maturation remains unclear. Discoidin domain receptor 1 (DDR1) is a nonintegrin collagen receptor constitutively expressed in a variety of epithelial cells, including tumor cells, and is inducible in leukocytes. In this study, we evaluated the role of DDR1 in DC maturation using human monocyte-derived DCs. Two DDR1 isoforms, DDR1a and DDR1b, were expressed in both immature and mature DCs. Activation of DDR1 on immature DCs resulted in their partial maturation; however, DDR1 activation markedly amplified TNF-alpha- and LPS-induced phenotypic and functional maturation of DCs through activation of p38 mitogen-activated protein kinase (MAPK), suggesting the involvement of DDR1b in this process. Activation of DDR1b on differentiated DDR1b-overexpressing THP-1 cells or DDR1 on mature DCs induced the formation of TNFR associated factor 6 (TRAF6)/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK complex and p38alpha autophosphorylation. Transfection of differentiated DDR1b-overexpressing THP-1 cells with dominant negative TRAF6 completely abrogated DDR1b-mediated p38 MAPK phosphorylation, indicating a critical role of TRAF6 in DDR1b-mediated p38 MAPK activation. Taken together, our data suggest that DDR1b-collagen interaction augments the maturation of DCs in a tissue microenvironment through a unique TRAF6/TGF-beta-activated kinase 1 binding protein 1beta/p38alpha MAPK signaling cascade and contributes to the development of adaptive immune responses.

Interaction of discoidin domain receptor 1 isoform b (DDR1b) with collagen activates p38 mitogen-activated protein kinase and promotes differentiation of macrophages

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase activated by collagen. DDR1 is constitutively expressed in a variety of normal and transformed epithelial cells and plays a role in cell migration and differentiation through as yet unidentified signaling pathways. We previously reported inducible expression of DDR1 in human leukocytes and suggested a role for the DDR1a isoform in leukocyte migration through extracellular matrix. Here, we evaluated the contribution of DDR1 in the differentiation of the human monocytic THP-1 cells overexpressing these isoforms and of primary macrophages. Interestingly, collagen activation of DDR1b, but not DDR1a, further promoted phorbol ester-induced differentiation of THP-1 cells as determined by reduced cell proliferation and up-regulated expression of HLA-DR, CD11c, CD14, and CD40. Collagen activation of DDR1b also induced the recruitment and phosphorylation of Shc and subsequent phosphorylation of p38 mitogen-activated protein (MAP) kinase and its substrate ATF2. A p38 MAP kinase inhibitor, SB203580, completely inhibited DDR1b-mediated HLA-DR expression. Activation of DDR1 endogenously expressed on macrophages also up-regulated their HLA-DR expression in a p38 MAP kinase-dependent manner. Thus, DDR1b in response to collagen transduces signals that promote maturation/differentiation of HLA-DR-positive antigen-presenting cells and contributes to the development of adaptive immunity in a tissue microenvironment.

Intracellular protein tyrosine phosphorylation of adherent human macrophages on adsorbed fibronectin

Fibronectin (FN) was pre-adsorbed onto physicochemically distinct substrates: polyethyleneglycol-based networks or tissue culture polystyrene (TCPS). The role of these substrates in modulating FN-mediated intracellular protein tyrosine phosphorylation and cell adhesion was analyzed with human primary blood derived macrophages. Although macrophage adhesion on both FN-pre-adsorbed TCPS and networks was similarly dependent on protein tyrosine kinase (PTK) and protein serine/threonine kinase (PSK), the compensation between PTK and PSK, and the involvement of signaling molecules (such as protein kinase C (PKC) isoforms) were distinct between the substrates. The pattern and the extent of tyrosine phosphorylation of several proteins (i.e. approximately 70, approximately 44, approximately 30kDa) were differentially regulated by PKCs. FN-derived peptides were employed to probe this material-dependency in macrophage adhesion and tyrosine phosphorylation. The PHSRN domain in the peptide sequence was predominant in mediating this substrate-dependent FN signaling event. We conclude that the tyrosine phosphorylation and the cross talk between PTK and PSK are modulated by FN and the substrate onto which the protein is adsorbed.

TNF-alpha protects dendritic cells from prostate cancer-induced apoptosis

We have recently shown that human prostate cancer (PCa) cells induced apoptotic death of the most potent antigen-presenting cells, dendritic cells (DC), which are responsible for the induction of specific antitumor immune responses. Here we have evaluated the effect of murine PCa cells RM-1 on the survival of immature and tumor necrosis factor-alpha (TNF-alpha)-stimulated mature DC. PCa cells and DC were co-incubated for 24-48 h and DC apoptosis was assessed by morphologic criteria, Annexin V assay, and TUNEL staining. We have shown that co-incubation of RM-1 cells with DC is accompanied by an increased level of DC apoptosis, which was mediated by decreased expression of anti-apoptotic protein Bcl-2. Stimulation of DC maturation by TNF-alpha resulted in increased resistance of DC to PCa-induced apoptosis. In TNF-alpha treated mature DC, but not in immature DC, the expression of Bcl-2 was not blocked after exposure to RM-1-derived factors. Thus, these data suggest that TNF-alpha-induced maturation of DC increases their resistance to PCa induced apoptosis. This is likely to be due to the stabilizing of the expression of anti-apoptotic protein Bcl-2. The difference in the sensitivity of mature and immature DC to PCa-induced cell death should be considered during the design of DC-based clinical trials for PCa patients.Prostate Cancer and Prostatic Diseases (2001) 4, 221-227.

Human macrophage adhesion on fibronectin: the role of substratum and intracellular signalling kinases

Fibronectin and Arg-Gly-Asp (RGD)- and/or Pro-His-Ser-Arg-Asn (PHSRN)-containing oligopeptides were immobilized onto physicochemically distinct substrata: polyethyleneglycol-based networks or tissue culture polystyrene (TCPS). The role of selected signalling kinases in the adhesion of human primary blood-derived macrophages on these modified substrata was investigated. We demonstrated that the protein tyrosine kinase (PTK) or protein serine/threonine kinase (PSK) dependency and the PTK-PSK cross-talk compensation for macrophage adhesion varied dynamically with the substratum modification and the culture time. The inhibition of MAPK kinase (MAPKK) decreased macrophage adhesion on TCPS, whereas the inhibition of phosphoinositide-3 kinase (PI3 kinase) decreased macrophage adhesion on networks at 24 h. The PI3 kinase-protein kinase C (PKC)-MAPK cascade was involved in macrophage adhesion on fibronectin-preadsorbed TCPS or networks but not on fibronectin-grafted networks. This fibronectin-mediated adhesion signalling involved both RGD and PHSRN sequences in a form of G(3)RGDG(6)PHSRNG on TCPS but not on networks. Furthermore, G(3)RGDG(6)PHSRNG grafted onto networks evoked unique signalling in macrophage adhesion from that preadsorbed onto networks. Thus, macrophage adhesion and the role of selected signalling kinases were modulated by the substratum and the ligand conjugation method.

Maturation-dependent expression and function of the CD49d integrin on monocyte-derived human dendritic cells

Dendritic cells (DC) are highly specialized APC that are critical for the initiation of T cell-dependent immune responses. DC exert a sentinel function while immature and, after activation by inflammatory stimuli or infectious agents, mature and migrate into lymphoid organs to prime T cells. We have analyzed integrin expression on monocyte-derived DC (MDDC) and found that expression of CD49d integrins (CD49d/CD29 and CD49d/beta7) was induced/up-regulated during TNF-alpha- or LPS-initiated MDDC maturation, reflecting the induction/up-regulation of CD49d and beta7 mRNA. CD49d mRNA steady-state level increased more than 10 times during maturation, with the highest levels observed 24 h after TNF-alpha treatment. CD49d integrin expression conferred mature MDDC with an elevated capacity to adhere to the CS-1 fragment of fibronectin, and also mediated transendothelial migration of mature MDDC. Up-regulation of CD49d integrin expression closely paralleled that of the mature DC marker CD83. CD49d integrin expression was dependent on cell maturation, as its induction was abrogated by N:-acetylcysteine, which inhibits NF-kappaB activation and the functional and phenotypic maturation of MDDC. Moreover, CD49d integrin up-regulation and MDDC maturation were prevented by SB203580, a specific inhibitor of p38 mitogen-activated protein kinase, but were almost unaffected by the mitogen-activated protein/extracellular signal-related kinase kinase 1/2 inhibitor PD98059. Our results support the existence of a link between functional and phenotypic maturation of MDDC and CD49d integrin expression, thus establishing CD49d as a maturation marker for MDDC. The differential expression of CD49d on immature and mature MDDC might contribute to their distinct motility capabilities and mediate mature DC migration into lymphoid organs.

Phenotypic and functional maturation of dendritic cells mediated by heparan sulfate

Primary immune responses are thought to be induced by dendritic cells. To promote such responses, dendritic cells must be activated by exogenous agonists, such as LPS, or by products of activated leukocytes, such as TNF-alpha and IL-1. How dendritic cells might be activated in the absence of exogenous stimuli, or without the immediate presence of activated leukocytes, as might occur in immunity to tumor cells or transplants, is unknown. We postulated that heparan sulfate, an acidic, biologically active polysaccharide associated with cell membranes and extracellular matrices, which is rapidly released under conditions of inflammation and tissue damage, might provide such a stimulus. Incubation of immature murine dendritic cells with heparan sulfate induced phenotypic maturation evidenced by up-regulation of I-A, CD40, CD54 (ICAM-1), CD80 (B7-1), and CD86 (B7-2). Dendritic cells exposed to heparan sulfate exhibited a markedly lowered rate of Ag uptake and increased allostimulatory capacity. Stimulation of dendritic cells with heparan sulfate induced release of TNF-alpha, IL-1beta, and IL-6, although the maturation of dendritic cells was independent of these cytokines. These results suggest that soluble heparan sulfate chains, as products of the degradation of heparan sulfate proteoglycan, might induce maturation of dendritic cells without exogenous stimuli, thus contributing to the generation and maintenance of primary immune responses.

Human blood monocytes interact with type I collagen through alpha x beta 2 integrin (CD11c-CD18, gp150-95)

Human blood monocytes are attracted into connective tissues during early steps of inflammation and wound healing, and locally interact with resident cells and extracellular matrix proteins. We studied the effects of type I collagen on monocyte adhesion and superoxide anion production, using human monocytes elutriated from peripheral blood and type I collagen obtained from rat tail tendon. Both acid-soluble and pepsin-digested type I collagens promoted the adhesion of monocytes, whereas only acid-soluble collagen with intact telopeptides induced the production of superoxide. Adhesion and activation of monocytes on acid-soluble type I collagen depended on the presence of divalent cations. mAbs directed against integrin subunits CD11c and CD18 specifically inhibited adhesion and activation of monocytes on type I collagen. Protein membrane extracts obtained from monocytes were submitted to affinity chromatography on collagen I-Sepharose 4B, and analyzed by Western blotting using specific anti-integrin subunit Abs. In the case of both acid-soluble and pepsin-digested collagens, two bands were revealed with mAbs against CD11c and CD18 integrin subunits. Our results demonstrate that monocytes interact with type I collagen through CD11c-CD18 (alpha x beta 2) integrins, which promote their adhesion and activation. For monocyte activation, specific domains of the type I collagen telopeptides are necessary. Interactions between monocytes and collagen are most likely involved in the cascade of events that characterize the initial phases of inflammation.

Allergen-specific immune deviation from a TH2 to a TH1 response induced by dendritic cells and collagen type I

BACKGROUND

Atopy and IgE production are associated with enhanced allergen-specific T(H)2 responses. Therefore a causative treatment may result from the deviation of this T(H)2-dominated immune response toward a T(H)1 response.

OBJECTIVE

This study was carried out to analyze whether dendritic cells, the most potent antigen-presenting cells that are also known to induce antigen-specific T(H)1 responses, are suitable for therapy of atopic diseases by shifting the allergen-specific T(H)2 response toward a T(H)1 response.

METHODS

Monocyte-derived dendritic cells were used to present allergens in vitro to autologous CD4(+) T cells of allergic persons. Because collagen type I activates dendritic cells and enhances the secretion of IL-12, we performed allergen presentation assays also in the presence of collagen type I.

RESULTS

After stimulation with allergen-pulsed dendritic cells the production of IFN-gamma as well as that of IL-4 and IL-5 by CD4(+) T cells was enhanced. In the presence of collagen type I, however, a significant shift toward a T(H)1 response with increased production of IFN-gamma and a decreased production of IL-5 could be observed. When T cells were stimulated directly with anti-CD3 and anti-CD28 in the absence of antigen-presenting cells, it was demonstrated that collagen type I also exerted a direct effect on T cells, increasing their IFN-gamma production.

CONCLUSION

These data indicate that collagen type I influences dendritic cells as well as T cells in a way that a shift in cytokine production results in a T(H)1 response even in already-sensitized atopic individuals.