Beta1 and beta2 integrins mediate adhesion during macrophage fusion and multinucleated foreign body giant cell formation

Paired Ig-Like Type 2 Receptor-Derived Agonist Ligands Ameliorate Inflammatory Reactions by Downregulating β1 Integrin Activity

The paired immunoglobulin-like type 2 receptor (PILR) family consists of two functionally opposite members, inhibitory PILRα and activating PILRβ receptors. PILRs are widely expressed in various immune cells and interact with their ligands, especially CD99 expressed on activated T cells, to participate in immune responses. Here we investigated whether PILR-derived agonists inhibit β1 integrin activity as ligands for CD99. PILR-derived peptides as well as PILR-Fc fusion proteins prevented cell adhesion to fibronectin through the regulation of β1 integrin activity. Especially, PILRpep3, a representative 3-mer peptide covering the conserved motifs of the PILR extracellular domain, prevented the clustering and activation of β1 integrin by dephosphorylating FAK and vinculin, which are major components of focal adhesion. In addition, PILRpep3 inhibited transendothelial migration of monocytes as well as endothelial cell tube formation. Furthermore, upon intraperitoneal injection of PILRpep3 into mice with collagen-induced arthritis, the inflammatory response of rheumatoid arthritis was strongly suppressed. Taken together, these results suggest that PILR-derived agonist ligands may prevent the inflammatory reactions of rheumatoid arthritis by activating CD99.

The Role of Integrins αMβ2 (Mac-1, CD11b/CD18) and αDβ2 (CD11d/CD18) in Macrophage Fusion

The subfamily of β2 integrins is implicated in macrophage fusion, a hallmark of chronic inflammation. Among β2 family members, integrin Mac-1 (αMβ2, CD11b/CD18) is abundantly expressed on monocyte/macrophages and mediates critical adhesive reactions of these cells. However, the role of Mac-1 in macrophage fusion leading to the formation of multinucleated giant cells remains unclear. Moreover, the role of integrin αDβ2 (CD11d/CD18), a receptor with recognition specificity overlapping that of Mac-1, is unknown. We found that multinucleated giant cells are formed in the inflamed mouse peritoneum during the resolution phase of inflammation, and their numbers were approximately twofold higher in wild-type mice than in Mac-1(-/-) mice. Analyses of isolated inflammatory peritoneal macrophages showed that IL-4-induced fusion of Mac-1-deficient cells was strongly reduced compared with wild-type counterparts. The examination of adhesive reactions known to be required for fusion showed that spreading, but not adhesion and migration, was reduced in Mac-1-deficient macrophages. Fusion of αDβ2-deficient macrophages was also significantly decreased, albeit to a smaller degree. Deficiency of intercellular adhesion molecule 1, a counter-receptor for Mac-1 and αDβ2, did not alter the fusion rate. The results indicate that both Mac-1 and αDβ2 support macrophage fusion with Mac-1 playing a dominant role and suggest that Mac-1 may mediate cell-cell interactions with a previously unrecognized counter-receptor(s).

Future challenges in the in vitro and in vivo evaluation of biomaterial biocompatibility

As the science and engineering of biomaterials continues to expand with increased emphasis on the development of nanomaterials and tissue engineering scaffolds, emphasis also must be placed on appropriate and adequate approaches to the in vivo and in vitro evaluation of biomaterial biocompatibility/biological response evaluation. This article presents six topic areas that should be addressed by investigators as they move forward in the development of new systems for regenerative medicine. Most certainly, there are other areas that require attention to detail and a more complete understanding of the strengths and weaknesses of various experimental approaches to biomaterial/biological response evaluation. The small number of issues addressed in this article is only meant to bring to the attention of prospective investigators and authors, the importance of the development of adequate and appropriate evaluation techniques that address the unique features of biomaterials utilized in the development of new medical devices.

Nanoparticle delivery of miR-223 to attenuate macrophage fusion

The foreign body response (FBR) begins with injury acquired during implantation of a biomaterial (BM) and is detrimental due to the eventual encapsulation of the implant. Fusion of macrophages to form foreign body giant cells (FBGC), a hallmark of the FBR, is the consequence of a multistep mechanism induced by interleukin (IL)-4 that includes the acquisition of a fusion competent state and subsequent cytoskeletal rearrangements. However, the precise mechanism, regulation, and interplay among molecular mediators to generate FBGCs are insufficiently understood. Seeking novel mediators of fusion that might be regulated at the post-transcriptional level, we examined the role of microRNAs (miRs) in this process. A miR microarray was screened and identified miR-223 as a negative regulator of macrophage fusion. In addition, transfection of primary macrophages with a mir-223 mimic attenuated IL-4-induced fusion. Furthermore, miR-223 KO mice and mir-223 deficient cells displayed increased fusion in vivo and in vitro, respectively. Finally, we developed a method for in vivo delivery of miR-223 mimic utilizing PLGA nanoparticles, which inhibited FBGC formation in a biomaterial implant model. Our results identify miR-223 as a negative regulator of fusion and demonstrate miR-223 mimic-loaded nanoparticles as a therapeutic inhibitor of macrophage fusion.

Covalent Immobilization of Glycosaminoglycans to Reduce the Inflammatory Effects of Biomaterials

Background

The inflammatory responses evoked by artificial organs and implantation of devices like biosensors and guide wires can lead to acute and chronic inflammation, largely limiting the functionality and longevity of the devices with negative effects on patients.

Aims

The present study aimed to reduce the inflammatory responses to biomaterials by covalent immobilization of glycosaminoglycans (GAGs) on amino-terminated surfaces used as model biomaterials here.

Methods and Results

Water contact angle (WCA) and zeta potential measurements showed a significant increase in wettability and negative charges on the GAG-modified surfaces, respectively, confirming the successful immobilization of GAGs on the amino-terminated surfaces. THP-1-derived macrophages were used as a model cell type to investigate the efficacy of GAG-modified surfaces in modulating inflammatory responses. It was found that macrophage adhesion, macrophage spreading morphology, foreign body giant cell (FBGC) formation, as well as β1 integrin expression and interleukin-1β (IL-1β) production were all significantly decreased on GAG-modified surfaces compared to the initial amino-terminated surface.

Conclusions

This study demonstrates the potential of covalent GAG immobilization to reduce the inflammatory potential of biomaterials in different clinical settings.

OsteoMacs: Key players around bone biomaterials

Osteal macrophages (OsteoMacs) are a special subtype of macrophage residing in bony tissues. Interesting findings from basic research have pointed to their vast and substantial roles in bone biology by demonstrating their key function in bone formation and remodeling. Despite these essential findings, much less information is available concerning their response to a variety of biomaterials used for bone regeneration with the majority of investigation primarily focused on their role during the foreign body reaction. With respect to biomaterials, it is well known that cells derived from the monocyte/macrophage lineage are one of the first cell types in contact with implanted biomaterials. Here they demonstrate extremely plastic phenotypes with the ability to differentiate towards classical M1 or M2 macrophages, or subsequently fuse into osteoclasts or multinucleated giant cells (MNGCs). These MNGCs have previously been characterized as foreign body giant cells and associated with biomaterial rejection, however more recently their phenotypes have been implicated with wound healing and tissue regeneration by studies demonstrating their expression of key M2 markers around biomaterials. With such contrasting hypotheses, it becomes essential to better understand their roles to improve the development of osteo-compatible and osteo-promotive biomaterials. This review article expresses the necessity to further study OsteoMacs and MNGCs to understand their function in bone biomaterial tissue integration including dental/orthopedic implants and bone grafting materials.

Multinucleated Giant Cells Are Specialized for Complement-Mediated Phagocytosis and Large Target Destruction

Multinucleated giant cells (MGCs) form by fusion of macrophages and are presumed to contribute to the removal of debris from tissues. In a systematic in vitro analysis, we show that IL-4-induced MGCs phagocytosed large and complement-opsonized materials more effectively than their unfused M2 macrophage precursors. MGC expression of complement receptor 4 (CR4) was increased, but it functioned primarily as an adhesion integrin. In contrast, although expression of CR3 was not increased, it became functionally activated during fusion and was located on the extensive membrane ruffles created by excess plasma membrane arising from macrophage fusion. The combination of increased membrane area and activated CR3 specifically equips MGCs to engulf large complement-coated targets. Moreover, we demonstrate these features in vivo in the recently described complement-dependent therapeutic elimination of systemic amyloid deposits by MGCs. MGCs are evidently more than the sum of their macrophage parts.

•

MGCs are specialized for phagocytosis of large and complement-opsonized particles

•

MGCs show extensive membrane ruffles containing pre-activated complement receptor 3

•

Membrane ruffles provide excess membrane for ingestion of large materials

•

MGCs eliminate systemic amyloid deposits after immunotherapeutic targeting

Update on macrophages and innate immunity in scleroderma

PURPOSE OF REVIEW

In this review of the literature from 2014 through mid-2015, we examine new data that shed light on how macrophages and other innate immune cells and signals contribute to inflammation, vascular dysfunction, and fibrosis in scleroderma.

RECENT FINDINGS

Recent human studies have focused on changes early in scleroderma, and linked macrophages to inflammation in skin and progression of lung disease. Plasmacytoid dendritic cells have been implicated in vascular dysfunction. In mice, several factors have been identified that influence macrophage activation and experimental fibrosis. However, emerging data also suggest that myeloid cells can have differential effects in fibrosis. Sustained signaling through different toll-like receptors can lead to inflammation or fibrosis, and these signals can influence both immune and nonimmune cells.

SUMMARY

There are many types of innate immune cells that can potentially contribute to scleroderma and will be worth exploring in detail. Experimentally dissecting the roles of macrophages based on ontogeny and activation state, and the innate signaling pathways in the tissue microenvironment, may also lead to better understanding of scleroderma pathogenesis.

A macrophage/fibroblast co-culture system using a cell migration chamber to study inflammatory effects of biomaterials

Chronic inflammatory reactions hamper the use of biomaterials after implantation. Thus, the aim of the study was to develop a novel predictive in vitro macrophage/fibroblast co-culture model based on cell migration chambers that allows a timely and locally controlled interaction of both cell types to study the inflammatory responses of biomaterials in vitro. Here, self-assembled monolayers (SAMs) with different wettability and charge properties were used as model biomaterials on which co-cultures were established by use of fence chambers having internal and external compartments. This allowed establishing separated and mixed co-cultures of both cell types before and after removal of the chamber, respectively. The key advantages of this novel co-culture model included not only to establish a timely-resolved study of cytokine release, but also the ability to assess individual macrophage migration in both macrophage mono-cultures and co-cultures. All inflammatory reactions in terms of macrophage adhesion, macrophage migration, foreign body giant cell (FBGC) formation, β1 integrin expression and pro-inflammatory cytokine production were found strongly surface property dependent. The results show that the hydrophobic CH3 surface caused the strongest inflammatory reactions, whereas the hydrophilic/anionic COOH surface caused the least inflammatory response, indicating low and high biocompatibility of the surfaces, respectively. Most importantly, we found that both macrophage motility and directional movement were increased in the presence of fibroblasts in co-cultures compared with macrophage mono-cultures. Overall, the novel co-culture system provides access to a range of parameters for studying inflammatory reactions and reveals how material surface properties affect the inflammatory responses.

Expression of CD11c in periprosthetic tissues from failed total hip arthroplasties

In this work, we characterize integrin CD11c (αXß2) expression in periprosthetic tissues of 45 hip revisions. Tissues were retrieved from 23 ceramic-on-ultra-high molecular weight polyethylene (UHMWPE), 20 metal-on-UHMWPE, and 2 metal-on-metal total hip arthroplasties (THAs). Capsular tissue retrieved during primary THA from 19 patients served as controls. We identified a system to identify important immunohistochemical markers that are expressed in aseptic loosening. We focused on CD11c, CD68 and CD14. We observed that the CD11c molecule possesses four different cellular patterns in the periprosthetic tissues. Three of them are associated with the occurrence of UHMWPE abrasive material. Double staining with CD14 and CD68 was used for a more detailed analysis of the CD11c expressing cells. We observed that all forms of CD11c positive cells are CD68 positive however, only two forms of CD11c expressing cells are positive for CD14. Providing cellular diversity of CD11c expression in periprosthetic tissue, our results provide a contribution toward the further understanding of different cellular mechanisms to foreign body material.

Phenotypic expression in human monocyte-derived interleukin-4-induced foreign body giant cells and macrophages in vitro: dependence on material surface properties

The effects of different material surfaces on phenotypic expression in macrophages and foreign body giant cells (FBGC) were addressed using our in vitro system of interleukin (IL)-4-induced macrophage fusion and FBGC formation. Arginine-glycine-aspartate (RGD)-, vitronectin (VN)-, and chitosan (CH)-adsorbed cell culture polystyrene, carboxylated (C, negatively charged) polystyrene, and unmodified (PS, non-cell culture treated) polystyrene were compared for their abilities to support monocyte/macrophage adhesion and IL-4-induced macrophage fusion. Pooled whole cell lysates from four different donors were evaluated by immunoblotting for expression of selected components in monocytes, macrophages, and FBGC. In addition to RGD and VN as previously shown, we find that CH supports macrophage adhesion and FBGC formation, whereas C or PS support macrophage adhesion but do not permit macrophage fusion under otherwise identical conditions of IL-4 stimulation. Likewise, components related to macrophage fusion (CD206, CD98, CD147, CD13) are strongly expressed on RGD-, VN-, and CH-adsorbed surfaces but are greatly diminished or not detected on C or PS. Importantly, material surfaces also influence the FBGC phenotype itself, as demonstrated by strong differences in patterns of expression of HLA-DR, B7-2, B7-H1, and toll-like receptor (TLR)-2 on RGD, VN, and CH despite morphologic similarities between FBGC on these surfaces. Likewise, we observe differences in the expression of B7-2, α2-macroglobulin, TLR-2, and fascin-1 between mononuclear macrophages on C and PS. Collectively, these findings reveal the extent to which material surface chemistry influences macrophage/FBGC phenotype beyond evident morphological similarities or differences and identify CH as an FBGC-supportive substrate.

Loss of monocyte chemoattractant protein-1 alters macrophage polarization and reduces NFκB activation in the foreign body response

Implantation of biomaterials elicits a foreign body response characterized by fusion of macrophages to form foreign body giant cells and fibrotic encapsulation. Studies of the macrophage polarization involved in this response have suggested that alternative (M2) activation is associated with more favorable outcomes. Here we investigated this process in vivo by implanting mixed cellulose ester filters or polydimethylsiloxane disks in the peritoneal cavity of wild-type (WT) and monocyte chemoattractant protein-1 (MCP-1) knockout mice. We analyzed classical (M1) and alternative (M2) gene expression via quantitative polymerase chain reaction, immunohistochemistry and enzyme-linked immunosorbent assay in both non-adherent cells isolated by lavage and implant-adherent cells. Our results show that macrophages undergo unique activation that displays features of both M1 and M2 polarization including induction of tumor necrosis factor α (TNF), which induces the expression and nuclear translocation of p50 and RelA determined by immunofluorescence and Western blot. Both processes were compromised in fusion-deficient MCP-1 KO macrophages in vitro and in vivo. Furthermore, inclusion of BAY 11-7028, an inhibitor of NFκB activation, reduced nuclear translocation of RelA and fusion in WT macrophages. Our studies suggest that peritoneal implants elicit a unique macrophage polarization phenotype leading to induction of TNF and activation of the NFκB pathway.

The significance of macrophage phenotype in cancer and biomaterials

Macrophages have long been known to exhibit heterogeneous and plastic phenotypes. They show functional diversity with roles in homeostasis, tissue repair, immunity and disease. There exists a spectrum of macrophage phenotypes with varied effector functions, molecular determinants, cytokine and chemokine profiles, as well as receptor expression. In tumor microenvironments, the subset of macrophages known as tumor-associated macrophages generates byproducts that enhance tumor growth and angiogenesis, making them attractive targets for anti-cancer therapeutics. With respect to wound healing and the foreign body response, there is a necessity for balance between pro-inflammatory, wound healing, and regulatory macrophages in order to achieve successful implantation of a scaffold for tissue engineering. In this review, we discuss the multitude of ways macrophages are known to be important in cancer therapies and implanted biomaterials.

Cultured human bone marrow-derived CD31(+) cells are effective for cardiac and vascular repair through enhanced angiogenic, adhesion, and anti-inflammatory effects

BACKGROUND

Cell therapy for cardiovascular disease has been limited by low engraftment of administered cells and modest therapeutic effects. Bone marrow (BM) -derived CD31(+) cells are a promising cell source owing to their high angiovasculogenic and paracrine activities.

OBJECTIVES

This study sought to identify culture conditions that could augment the cell adhesion, angiogenic, and anti-inflammatory activities of BM-derived CD31(+) cells, and to determine whether these cultured CD31(+) cells are effective for cardiac and vascular repair.

METHODS

CD31(+) cells were isolated from human BM by magnetic-activated cell sorting and cultured for 10 days under hematopoietic stem cell, mesenchymal stem cell, or endothelial cell culture conditions. These cells were characterized by adhesion, angiogenesis, and inflammatory assays. The best of the cultured cells were implanted into myocardial infarction (MI) and hindlimb ischemia (HLI) models to determine therapeutic effects and underlying mechanisms.

RESULTS

The CD31(+) cells cultured in endothelial cell medium (EC-CD31(+) cells) showed the highest adhesion and angiogenic activities and lowest inflammatory properties in vitro compared with uncultured or other cultured CD31(+) cells. When implanted into mouse MI or HLI models, EC-CD31(+) cells improved cardiac function and repaired limb ischemia to a greater extent than uncultured CD31(+) cells. Histologically, injected EC-CD31(+) cells exhibited higher retention, neovascularization, and cardiomyocyte proliferation. Importantly, cell retention and endothelial transdifferentiation was sustained up to 1 year.

CONCLUSIONS

Short-term cultured EC-CD31(+) cells have higher cell engraftment, vessel-formation, cardiomyocyte proliferation, and anti-inflammatory potential, are highly effective for both cardiac and peripheral vascular repair, and enhance survival of mice with heart failure. These cultured CD31(+) cells may be a promising source for treating ischemic cardiovascular diseases.

Additive effect of recombinant Mycobacterium tuberculosis ESAT-6 protein and ESAT-6/CFP-10 fusion protein in adhesion of macrophages through fibronectin receptors

BACKGROUND/PURPOSE

Tuberculous granulomas are the sites of interaction between the T cells, macrophages, and extracellular matrix (ECM) to control the infection caused by Mycobacterium tuberculosis (M. tuberculosis). A predominant role of RD-1-encoded secretory proteins, early secreted antigenic target-6 (ESAT-6), and culture filtrate protein-10 (CFP-10) in the formation of granulomas has recently been emphasized. However, the precise molecular events that induce the formation of these granulomatous structures are yet to be elucidated. Macrophages use integrins to adhere to fibronectin (FN) as a major component of the ECM. The major goal of this study was to investigate whether recombinant M. tuberculosis antigens can modulate integrin-mediated macrophage adhesion.

METHODS

Differentiated THP-1 cell line was stimulated with recombinant ESAT-6, CFP-10, and ESAT-6/CFP-10 proteins and evaluated for alterations in the expression levels of α5β1 and α4β1 by semiquantitative real-time polymerase chain reaction. The role of these recombinant antigens in the cytoskeleton rearrangement was determined by adhesion assay and immunofluorescent microscopy.

RESULTS

Our data showed that ESAT-6 and ESAT-6/CFP-10 fusion proteins could induce adhesion of macrophages to FN through α4β1 integrin. An increased expression level of α4β1 integrin in comparison with α5β1 integrin in differentiated THP-1 cells was also observed. Results of immunofluorescence studies showed that recombinant proteins-treated THP-1 cells form well-organized stress fibers and focal contacts containing vinculin compared with untreated THP-1 cells.

CONCLUSION

Increased expression level of α4β1 in differentiated THP-1 cells could suggest the important role of α4β1 integrin in adhesion and focal contact formation of macrophages exposed to M. tuberculosis antigens.

In vitro expression of IL-1α, GM-CSF, and TNF-α by multinucleated macrophages from BCG-infected mice

Peritoneal cells from intact and BCG-infected mice were explanted in vitro. In these cultures, multinucleated macrophages in different number of nuclei were formed. The intensity of multinucleated cell formation was higher in cultures from BCG-infected mice. Increasing role of amitosis in the formation of multinucleated macrophages with relatively high number of nuclei was noted with presumable domination of cell fusion mechanism. Relatively high level of IL-1α expression was noted only in the population of binucleated macrophages of BCG-infected mice in comparison with mononuclear cells. It was found macrophages from BCG-infected mice demonstrate a kind of "lineage commitment" towards multinucleated cells, which manifested in culture in initially high and increasing (with increasing the number of nuclei in cells) expression of granulocyte-macrophage CSF and TNF-α as well as initially high amitotic activity of macrophages.

Integrin-directed modulation of macrophage responses to biomaterials

Macrophages are the primary mediator of chronic inflammatory responses to implanted biomaterials, in cases when the material is either in particulate or bulk form. Chronic inflammation limits the performance and functional life of numerous implanted medical devices, and modulating macrophage interactions with biomaterials to mitigate this response would be beneficial. The integrin family of cell surface receptors mediates cell adhesion through binding to adhesive proteins nonspecifically adsorbed onto biomaterial surfaces. In this work, the roles of integrin Mac-1 (αMβ2) and RGD-binding integrins were investigated using model systems for both particulate and bulk biomaterials. Specifically, the macrophage functions of phagocytosis and inflammatory cytokine secretion in response to a model particulate material, polystyrene microparticles were investigated. Opsonizing proteins modulated microparticle uptake, and integrin Mac-1 and RGD-binding integrins were found to control microparticle uptake in an opsonin-dependent manner. The presence of adsorbed endotoxin did not affect microparticle uptake levels, but was required for the production of inflammatory cytokines in response to microparticles. Furthermore, it was demonstrated that integrin Mac-1 and RGD-binding integrins influence the in vivo foreign body response to a bulk biomaterial, subcutaneously implanted polyethylene terephthalate. A thinner foreign body capsule was formed when integrin Mac-1 was absent (~30% thinner) or when RGD-binding integrins were blocked by controlled release of a blocking peptide (~45% thinner). These findings indicate integrin Mac-1 and RGD-binding integrins are involved and may serve as therapeutic targets to mitigate macrophage inflammatory responses to both particulate and bulk biomaterials.

Adsorbed fibrinogen enhances production of bone- and angiogenic-related factors by monocytes/macrophages

Macrophages are phagocytic cells with great importance in guiding multiple stages of inflammation and tissue repair. By producing a large number of biologically active molecules, they can affect the behavior of other cells and events, such as the foreign body response and angiogenesis. Since protein adsorption to biomaterials is crucial for the inflammatory process, we addressed the ability of the pro-inflammatory molecule fibrinogen (Fg) to modulate macrophage behavior toward tissue repair/regeneration. For this purpose, we used chitosan (Ch) as a substrate for Fg adsorption. Freshly isolated human monocytes were seeded on Ch substrates alone or previously adsorbed with Fg, and allowed to differentiate into macrophages for 10 days. Cell adhesion and morphology, formation of foreign body giant cells (FBGC), and secretion of a total of 80 cytokines and growth factors were evaluated. Both substrates showed similar numbers of adherent macrophages along differentiation as compared with RGD-coated surfaces, which were used as positive controls. Fg did not potentiate FBGC formation. In addition, actin cytoskeleton staining revealed the presence of punctuate F-actin with more elongated and interconnecting cells on Ch substrates. Antibody array screening and quantification of inflammation- and wound-healing-related factors indicated an overall reduction in Ch-based substrates versus RGD-coated surfaces. At late times, most inflammatory agents were down-regulated in the presence of Fg, in contrast to growth factor production, which was stimulated by Fg. Importantly, on Ch+Fg substrates, fully differentiated macrophages produced significant amounts of macrophage inflammatory protein-1delta (MIP-1δ), platelet-derived growth factor-BB, bone morphogenetic protein (BMP)-5, and BMP-7 compared with Ch alone. In addition, other important factors involved in bone homeostasis and wound healing, such as growth hormone, transforming growth factor-β3, and insulin-like growth factor-binding proteins, as well as several angiogenic mediators, including endocrine gland-derived vascular endothelial factor, fibroblast growth factor-7, and placental growth factor, were significantly promoted by Fg. This work provides a new perspective on the inflammatory response in the context of bone repair/regeneration mediated by a pro-inflammatory protein (Fg) adsorbed onto a biomaterial (Ch) that does not otherwise exhibit osteogenic properties.

The recognition of biomaterials: pattern recognition of medical polymers and their adsorbed biomolecules

All biomedical materials are recognized as foreign entities by the host immune system despite the substantial range of different materials that have been developed by material scientists and engineers. Hydrophobic biomaterials, hydrogels, biomaterials with low protein binding surfaces, and those that readily adsorb a protein layer all seem to incite similar host responses in vivo that may differ in magnitude, but ultimately result in encapsulation by fibrotic tissue. The recognition of medical materials by the host is explained by the very intricate pattern recognition system made up of integrins, toll-like receptors, scavenger receptors, and other surface proteins that enable leukocytes to perceive almost any foreign body. In this review, we describe the various pattern recognition receptors and processes that occur on biomedical material surfaces that permit detection of a range of materials within the host.

Macrophage fusion is controlled by the cytoplasmic protein tyrosine phosphatase PTP-PEST/PTPN12

Macrophages can undergo cell-cell fusion, leading to the formation of multinucleated giant cells and osteoclasts. This process is believed to promote the proteolytic activity of macrophages toward pathogens, foreign bodies, and extracellular matrices. Here, we examined the role of PTP-PEST (PTPN12), a cytoplasmic protein tyrosine phosphatase, in macrophage fusion. Using a macrophage-targeted PTP-PEST-deficient mouse, we determined that PTP-PEST was not needed for macrophage differentiation or cytokine production. However, it was necessary for interleukin-4-induced macrophage fusion into multinucleated giant cells in vitro. It was also needed for macrophage fusion following implantation of a foreign body in vivo. Moreover, in the RAW264.7 macrophage cell line, PTP-PEST was required for receptor activator of nuclear factor kappa-B ligand (RANKL)-triggered macrophage fusion into osteoclasts. PTP-PEST had no impact on expression of fusion mediators such as β-integrins, E-cadherin, and CD47, which enable macrophages to become fusion competent. However, it was needed for polarization of macrophages, migration induced by the chemokine CC chemokine ligand 2 (CCL2), and integrin-induced spreading, three key events in the fusion process. PTP-PEST deficiency resulted in specific hyperphosphorylation of the protein tyrosine kinase Pyk2 and the adaptor paxillin. Moreover, a fusion defect was induced upon treatment of normal macrophages with a Pyk2 inhibitor. Together, these data argue that macrophage fusion is critically dependent on PTP-PEST. This function is seemingly due to the ability of PTP-PEST to control phosphorylation of Pyk2 and paxillin, thereby regulating cell polarization, migration, and spreading.

Actin-propelled invasive membrane protrusions promote fusogenic protein engagement during cell-cell fusion

Cell-cell fusion is critical for the conception, development, and physiology of multicellular organisms. Although cellular fusogenic proteins and the actin cytoskeleton are implicated in cell-cell fusion, it remains unclear whether and how they coordinate to promote plasma membrane fusion. We reconstituted a high-efficiency, inducible cell fusion culture system in the normally nonfusing Drosophila S2R+ cells. Both fusogenic proteins and actin cytoskeletal rearrangements were necessary for cell fusion, and in combination they were sufficient to impart fusion competence. Localized actin polymerization triggered by specific cell-cell or cell-matrix adhesion molecules propelled invasive cell membrane protrusions, which in turn promoted fusogenic protein engagement and plasma membrane fusion. This de novo cell fusion culture system reveals a general role for actin-propelled invasive membrane protrusions in driving fusogenic protein engagement during cell-cell fusion.

The effect of adsorbed fibronectin and osteopontin on macrophage adhesion and morphology on hydrophilic and hydrophobic model surfaces

Macrophages play a crucial role in the host response to biomaterials. Here we investigated the effect of adsorbed fibronectin (FN) and osteopontin (OPN), two important proteins for tissue repair, on macrophage adhesion and morphology. Since cell-biomaterial interactions are modulated via proteins adsorbed onto biomaterial surfaces, FN and OPN were adsorbed on model self-assembled monolayers (SAMs) of alkanethiols on gold with different functional terminal groups (CH(3), OH and tetra(ethylene-glycol)). The initial interaction of inflammatory cells with a biomaterial is crucial for the ensuing phases of an inflammatory reaction. For this reason short-term cultures of primary human macrophages were performed. To account for the competitive adsorption of other proteins serum was added to the culture medium and the effect compared with serum-free medium cultures. In the presence of serum hydrophilic surfaces increased macrophage adhesion. In particular, FN induced a higher cell density, while OPN tended to decrease it. In serum-free medium cell adhesion was greater on hydrophobic surfaces, except for OPN-coated SAMs. Importantly, FN no longer enhanced macrophage adhesion, while OPN maintained its inhibitory effect. Cell polarization studies indicated that macrophage morphology variations induced by surface chemistry are overcome by pre-adsorbed OPN. Taken together our results show that in the presence of serum macrophage adhesion is promoted by FN hydrophilic surfaces, but impaired on OPN-coated surfaces. The effects of inhibited macrophage adhesion on macrophage fusion, and its relevance to the initial stages of the inflammatory response to biomaterials are discussed.

Rho GTPase protein expression and activation in murine monocytes/macrophages is not modulated by model biomaterial surfaces in serum-containing in vitro cultures

The Rho GTPase cellular signaling cascade was investigated in pro-monocyte and (monocyte-)macrophage cells by examining GTPase expression and activation in serum-containing cultures on model biomaterials. Abundance of Rho GDI and the Rho GTPase proteins RhoA, Cdc42 and Rac1 was determined in cells grown on tissue culture polystyrene, polystyrene, poly-l-lactide and Teflon(®) AF surfaces. Protein expression was compared based on cell maturity (pro-monocyte to monocyte to macrophage lineages) and by model surface chemistry: Rho proteins were present in the majority of macrophage cells tested on model surfaces suggesting that a pool of Rho proteins is readily available for signaling events in response to numerous activating cues, including biomaterials surface encounter. Rho GTPase activation profiles in these cell lines indicate active Cdc42 and Rho proteins in RAW 264.7, Rac1 and Rho in J774A.1, and Cdc42 and Rac1 in IC-21 cell lines, respectively. Collectively, these proteins are known to play critical roles in all actin-based cytoskeletal rearrangement necessary for cell adhesion, spreading and motility, and remain important to establishing cellular responses required for foreign body reactions in vivo. Differences in Rho GTPase protein expression levels based on cell sourcing (primary versus secondary-derived cell source), or as a function of surface chemistry were insignificant. Rho GTPase expression profiles varied between pro-monocytic non-adherent precursor cells and mature adherent monocyte/macrophage cells. The active GTP-bound forms of the Rho GTPase proteins were detected from monocyte-macrophage cell lines RAW 264.7 and J774A.1 on all polymer surfaces, suggesting that while these proteins are central to cell adhesive behavior, differences in surface chemistry are insufficient to differentially regulate GTPase activation in these cell types. Active Cdc42 was detected from cells cultured on the more-polar tissue culture polystyrene and poly-l-lactide surfaces after several days, but absent from those grown on apolar polystyrene and Teflon(®) AF, indicating some surface influence on this GTPase in serum-containing cultures.

The effects of substrate stiffness on the in vitro activation of macrophages and in vivo host response to poly(ethylene glycol)-based hydrogels

Poly(ethylene glycol) (PEG) hydrogels, modified with RGD, are promising platforms for cell encapsulation and tissue engineering. While these hydrogels offer tunable mechanical properties, the extent of the host response may limit their in vivo applicability. The overall objective was to characterize the effects of hydrogel stiffness on the in vitro macrophage response and in vivo host response. We hypothesized that stiffer substrates induce better attachment, adhesion, and increased cell spreading, which elevates the macrophage classically activated phenotype and leads to a more severe foreign body reaction (FBR). PEG-RGD hydrogels were fabricated with compressive moduli of 130, 240, and 840 kPa, and the same RGD concentration. Hydrogel stiffness did not impact macrophage attachment, but elicited differences in cell morphology. Cells retained a round morphology on 130 kPa substrates, with localized and dense F-actin and localized α(V) integrin stainings. Contrarily, cells on stiffer substrates were more spread, with filopodia protruding from the cell, a more defined F-actin, and greater α(V) integrin staining. When stimulated with lipopolysaccharide, macrophages had a classical activation phenotype, with increased expression of TNF-α, IL-1β, and IL-6, however the degree of activation was significantly reduced with the softest hydrogels. A FBR ensued in response to all hydrogels when implanted subcutaneously in mice, but 28 days postimplantation the layer of macrophages at the implant surface was significantly lower in the softest hydrogels. In conclusion, hydrogels with lower stiffness led to reduced macrophage activation and a less severe and more typical FBR, and therefore are more suited for in vivo tissue engineering applications.

Foreign body-type multinucleated giant cells induced by interleukin-4 express select lymphocyte co-stimulatory molecules and are phenotypically distinct from osteoclasts and dendritic cells

Foreign body-type multinucleated giant cells (FBGC), formed by macrophage fusion, are a prominent cell type on implanted biomaterials, although the roles they play at these and other sites of chronic inflammation are not understood. Why lymphocytes are present in this scenario and the effects of fusing macrophages/FBGC on subsequent lymphocyte responses are also unclear. To address the physiological significance of FBGC in this regard, we employed our in vitro system of interleukin (IL)-4-induced human monocyte-derived macrophage fusion/FBGC formation. Initially, we pursued the identities of lymphocyte co-stimulatory molecules on fusing macrophages/FBGC. In addition, we further compared the FBGC phenotype to that currently associated with osteoclasts and dendritic cells using recognized markers. Immunoblotting of cell lysates and immunochemistry of macrophages/FBGC in situ, revealed that IL-4-induced macrophages/FBGC strongly express HLA-DR, CD98, B7-2 (CD86), and B7-H1 (PD-L1), but not B7-1 (CD80) or B7-H2 (B7RP-1). Furthermore, molecules currently recognized to be expressed on osteoclasts (calcitonin receptor, tartrate-resistant acid phosphatase, RANK) or dendritic cells (CD1a, CD40, CD83, CD95/fas) are undetectable. In contrast, fusing macrophages/FBGC strongly express the macrophage markers αX integrin (CD11c), CD68, and dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN), whereas CD14 is completely down-modulated with IL-4-induced macrophage fusion. These novel data demonstrate that IL-4-induction of macrophage multinucleation/FBGC formation features the acquisition of a CD14-negative phenotypic profile which is distinguishable from that of dendritic cells and osteoclasts, yet potentially exhibits multiple capacities for lymphocyte interactions with resultant lymphocyte down-modulation.

Multinucleated giant cells from fibroblast cultures

Many multinucleated giant cells are well-known to form from macrophage origin. Those formed from other cell types are less described, but may be as prevalent in pathological tissue. Giant multinucleated cells derived from secondary and primary fibroblast sources in various cultures with similar characteristics to foreign body giant cells are reported. Secondary-transformed NIH 3T3 fibroblasts rapidly fuse within 24 h in contact co-cultures with RAW 264.7 immortalized macrophages, while 3T3 monocultures, non-contact (transwell) co-cultures, and macrophage-conditioned media-treated 3T3 monocultures all do not fuse. Primary-derived murine fibroblasts also form multinucleated cells, both in the presence or absence of co-cultured macrophages that increase during long-term culture (5-30 days). In contrast to 3T3 fusion, this primary cell phenomenon is not due to fibroblast fusion, but rather to nuclear division without cytokinesis. That these multinucleated fibroblasts can originate via different mechanisms may influence and distinguish their behaviors in conditions under which they may arise, including various in vitro culture assays, and in certain fibroblastic pathologies such as the foreign body response, fibrosis, cancer and aged tissue.

Molecular and cellular mechanisms of mammalian cell fusion

The fusion of one cell with another occurs in development, injury and disease. Despite the diversity of fusion events, five steps in sequence appear common. These steps include programming fusion-competent status, chemotaxis, membrane adhesion, membrane fusion, and post-fusion resetting. Recent advances in the field start to reveal the molecules involved in each step. This review focuses on some key molecules and cellular events of cell fusion in mammals. Increasing evidence demonstrates that membrane lipid rafts, adhesion proteins and actin rearrangement are critical in the final step of membrane fusion. Here we propose a new model for the formation and expansion of membrane fusion pores based on recent observations on myotube formation. In this model, membrane lipid rafts first recruit adhesion molecules and align with opposing membranes, with the help of a cortical actin "wall" as a rigid supportive platform. Second, the membrane adhesion proteins interact with each other and trigger actin rearrangement, which leads to rapid dispersion of lipid rafts and flow of a highly fluidic phospholipid bilayer into the site. Finally, the opposing phospholipid bilayers are then pushed into direct contact leading to the formation of fusion pores by the force generated through actin polymerization. The actin polymerization generated force also drives the expansion of the fusion pores. However, several key questions about the process of cell fusion still remain to be explored. The understanding of the mechanisms of cell fusion may provide new opportunities in correcting development disorders or regenerating damaged tissues by inhibiting or promoting molecular events associated with fusion.

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.

Macrophage fusion and multinucleated giant cells of inflammation

Macrophages undergo fusion with other macrophages to form the hallmark multinucleated giant cells of chronic inflammation. However, neither the existence of distinct morphological types of giant cells, the signaling pathways that induce their formation, the molecular mechanism(s) of macrophage fusion, nor the significance of macrophage multinucleation at chronic inflammatory sites are well understood. Our efforts have been focused on these unknowns, particularly as they relate to the foreign body-type giant cells that form on implanted biomaterials and biomedical devices. We have pursued the discoveries of human macrophage fusion factors (interleukin-4, interleukin-13, α-tocopherol) with emphasis on foreign body giant cells, and identified adhesion receptors and signaling intermediates, as well as an adhesion protein substrate (vitronectin) that supports macrophage fusion. Studies on the molecular mechanism of macrophage fusion have revealed it to be a mannose receptor-mediated phagocytic process with participation of the endoplasmic reticulum. Further phenotypic and functional investigations will foster new perspectives on these remarkable multinucleated cells and their physiological significances in multiple inflammatory processes.

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.

Effect of subcutaneous glucose sensor implantation on skin mRNA expression in pigs

BACKGROUND

Tight glycemic control has the potential to reduce long- and short-term effects of diabetes mellitus. New and improved glucose sensors for short-term implantation in the subcutis offer an alternative to the classical self-monitored blood glucose concentration in the management of diabetes. The use of glucose sensors has an advantage over the latter due to its capacity to obtain continuous glucose measurements. However, instability of in vivo glucose sensor measurements has been reported, and this bioinstability is likely to be influenced by the inflammatory reaction to the implanted sensor. Gene expression analysis is now performed in an existing porcine model of subcutaneous glucose sensor implantation to investigate the time course of inflammation from a new perspective.

METHODS

Tissue surrounding glucose sensors was sampled to different time points (2 h, 24 h, 3 days, and 7 days) after implantation in the subcutis of pigs. From the tissue RNA was extracted, cDNA was synthesized, and real-time reverse transcription-polymerase chain reaction (RT-PCR) was performed for the quantification of immunoregulatory genes.

RESULTS

Genes coding for adhesion molecules, chemokines, cytokines, CD markers, and antigen presentation molecules were differentially expressed over time. Most of the investigated genes were significantly up-regulated 24 h and 7 days after implantation.

CONCLUSIONS

The present study demonstrated that the technology for targeted multiple-gene expression by real-time RT-PCR is useful in the evaluation of the immune response to subcutaneously implanted glucose sensors and that the expression levels also seemed to correspond to the histomorphological observations over time.

Polymorphonuclear leukocyte inhibition of monocytes/macrophages in the foreign body reaction

The effect of polymorphonuclear leukocytes (PMNs) on the subsequent chronic phase macrophage-mediated foreign body reaction has not been previously investigated. Furthermore, while monocyte/macrophage-produced cytokines such as GM-CSF, G-CSF, or IL-1beta have been shown to increase PMN survival in vitro, few studies have examined the impact of directly cocultured monocytes/macrophages on PMN viability. To this end, we used our established in vitro system of interleukin (IL)-4-induced monocyte-derived macrophage fusion to examine the role of PMNs in the subsequent foreign body reaction. Monocytes were directly cultured with PMNs for 3 days before the addition of IL-4 to induce monocyte-derived macrophage fusion to facilitate foreign body giant cell (FBGC) formation by days 7 and 10 of culture. Optical microscopy was used to quantitatively determine adherent monocyte density, percent macrophage fusion, and FBGC density. A colorimetric MTT assay was used to assess PMN viability for direct cocultures of monocytes/macrophages and PMNs. Our results strongly suggest that the presence of PMNs inhibit IL-4-induced macrophage fusion and FBGC formation. Additionally, our findings demonstrate that cocultures containing PMNs and monocytes/macrophages increases PMN survival with respect to PMN-only cultures in vitro.

Chronic inflammatory responses to microgel-based implant coatings

Inflammatory responses to implanted biomedical devices elicit a foreign body fibrotic reaction that limits device integration and performance in various biomedical applications. We examined chronic inflammatory responses to microgel conformal coatings consisting of thin films of poly(N-isopropylacrylamide) hydrogel microparticles cross-linked with poly(ethylene glycol) diacrylate deposited on poly(ethylene terephthalate) (PET). Unmodified and microgel-coated PET disks were implanted subcutaneously in rats for 4 weeks and explants were analyzed by histology and immunohistochemistry. Microgel coatings reduced chronic inflammation and resulted in a more mature/organized fibrous capsule. Microgel-coated samples exhibited 22% thinner fibrous capsules that contained 40% fewer cells compared to unmodified PET disks. Furthermore, microgel-coated samples contained significantly higher levels of macrophages (80%) than unmodified PET controls. These results demonstrate that microgel coatings reduce chronic inflammation to implanted biomaterials. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

The glycoprotein B disintegrin-like domain binds beta 1 integrin to mediate cytomegalovirus entry

Cellular integrins were identified as human cytomegalovirus (HCMV) entry receptors and signaling mediators in both fibroblasts and endothelial cells. The goal of these studies was to determine the mechanism by which HCMV binds to cellular integrins to mediate virus entry. HCMV envelope glycoprotein B (gB) has sequence similarity to the integrin-binding disintegrin-like domain found in the ADAM (a disintegrin and metalloprotease) family of proteins. To test the ability of this region to bind to cellular integrins, we generated a recombinant soluble version of the gB disintegrin-like domain (gB-DLD). The gB-DLD protein bound to human fibroblasts in a specific, dose-dependent and saturable manner that required the expression of an intact beta1 integrin ectodomain. Furthermore, a physical association between gB-DLD and beta1 integrin was demonstrated through in vitro pull-down assays. The function of this interaction was shown by the ability of cell-bound gB-DLD to efficiently block HCMV entry and the infectivity of multiple in vivo target cells. Additionally, rabbit polyclonal antibodies raised against gB-DLD neutralized HCMV infection. Mimicry of the ADAM family disintegrin-like domain by HCMV gB represents a novel mechanism for integrin engagement by a virus and reveals a unique therapeutic target for HCMV neutralization. The strong conservation of the DLD across beta- and gammaherpesviruses suggests that integrin recognition and utilization may be a more broadly conserved feature throughout the Herpesviridae.

The topographical effect of electrospun nanofibrous scaffolds on the in vivo and in vitro foreign body reaction

Topographical cues play an important role in influencing cellular behavior and are considered as significant parameters to be controlled in tissue engineering applications. This work investigated the biocompatibility with regard to scaffold architecture and topographical effect of nanofibrous scaffolds on the in vivo and in vitro foreign body reaction. Random and aligned polycaprolactone (PCL) nanofibers were fabricated by electrospinning technique, with diameters of 313 +/- 5 nm and 506 +/- 24 nm, respectively. Primary monocytes isolated from five human donors were cultured on PCL nanofibers, PCL film, and RGD-coated glass in vitro and cell density and morphology was evaluated at time points of day 0 (2 h), day 3, day 7, and day 10. The in vivo study was carried out by implanting PCL nanofibers and film scaffolds subcutaneously in rats to test the biocompatibility and host response at time points of week 1, week 2, and week 4. The in vitro studies revealed that the initial monocyte adhesion on the aligned fiber scaffold was significantly less (p < 0.001) when compared to the random fiber scaffold. The in vivo study showed that the thicknesses of fibrous capsule on fibrous scaffolds were 7.55 +/- 0.54 microm for aligned fibers and 4.13 +/- 0.31 microm for random fibers, which were significantly thinner than that of film implants 37.7 +/- 0.25 microm (p < 0.001). Additionally, cell infiltration was observed in aligned fibrous scaffolds both in vitro and in vivo, while on random fibers and films, distinct fibrous capsule boundaries were found on the surfaces. These results indicate that aligned electrospun nanofibers may serve as a promising scaffold for tissue engineering by minimizing host response, enhancing tissue-scaffold integration, and eliciting a thinner fibrous capsule.

Comparative characterization of cultures of primary human macrophages or dendritic cells relevant to biomaterial studies

Macrophages are central mediators of biomaterial-associated wound healing. Dendritic cells (DCs) link innate and adaptive immunity and are important in the context of the host response to combination products. Starting with human peripheral blood mononuclear cells (PBMCs), DCs were derived from monocytes upon culture with granulocyte macrophage colony-stimulating factor and interleukin-4; macrophages were derived from monocytes upon culture without cytokines. Macrophage or DC cultures were characterized at relevant timepoints in both adherent and nonadherent fractions on control Primaria surfaces to characterize and define these inflammatory/immune cells as a prequel to their use in in vitro test biomaterial-host response studies. At day 10 (typical time for harvesting macrophages for subsequent treatment with test biomaterials), macrophages were CD11c+, macrophage mannose receptor (MMR)+, CD14+, and CD64+. At day 6 (typical time for harvesting of DCs after 24-h treatment with test biomaterials), DCs were CD1c+, CD11c+, CD123+, MMR+, CD14+, and CD64-. Furthermore, CD3+ and CD4+ T lymphocytes and CD19+ and CD24+ B lymphocytes were present in both cultures at all timepoints, although to different extents. Immature DCs (approximately 15 microm), were rounded but presented extensive dendritic processes upon maturation with lipopolysaccharide. Alternatively, adherent macrophages (approximately 15-20 microm) displayed internalized lipids and exhibited few membrane processes. The characterization and comparison of existing techniques to establish reliable, reproducible primary cultures of DCs or macrophages provides an important basis for examining and interpreting complex macrophage/DC-lymphocyte-orchestrated host responses in future studies with equivalent cell populations on test biomaterials.

Characterization of topographical effects on macrophage behavior in a foreign body response model

Current strategies to limit macrophage adhesion, fusion and fibrous capsule formation in the foreign body response have focused on modulating material surface properties. We hypothesize that topography close to biological scale, in the micron and nanometric range, provides a passive approach without bioactive agents to modulate macrophage behavior. In our study, topography-induced changes in macrophage behavior was examined using parallel gratings (250 nm-2 mum line width) imprinted on poly(epsilon-caprolactone) (PCL), poly(lactic acid) (PLA) and poly(dimethyl siloxane) (PDMS). RAW 264.7 cell adhesion and elongation occurred maximally on 500 nm gratings compared to planar controls over 48 h. TNF-alpha and VEGF secretion levels by RAW 264.7 cells showed greatest sensitivity to topographical effects, with reduced levels observed on larger grating sizes at 48 h. In vivo studies at 21 days showed reduced macrophage adhesion density and degree of high cell fusion on 2 mum gratings compared to planar controls. It was concluded that topography affects macrophage behavior in the foreign body response on all polymer surfaces examined. Topography-induced changes, independent of surface chemistry, did not reveal distinctive patterns but do affect cell morphology and cytokine secretion in vitro, and cell adhesion in vivo particularly on larger size topography compared to planar controls.

Vascular smooth muscle cell motility: From migration to invasion

Over the past decade, extensive research has focused on identifying the molecular mechanisms and signal transduction pathways involved in the modulation of vascular smooth muscle cell phenotypes. In the present review, the characteristics of vascular smooth muscle cell (VSMC) phenotypes as they relate to cell migration are discussed based on insights from recent molecular findings. A central theme is the mechanisms involved in nonpathogenic VSMC migration during tissue repair versus VSMC invasion that leads to the development of vascular diseases. The issue of how various factors that are released locally following tissue injury influence cell migration will also be addressed.

Plasticity of cell migration: a multiscale tuning model

Cell migration underlies tissue formation, maintenance, and regeneration as well as pathological conditions such as cancer invasion. Structural and molecular determinants of both tissue environment and cell behavior define whether cells migrate individually (through amoeboid or mesenchymal modes) or collectively. Using a multiparameter tuning model, we describe how dimension, density, stiffness, and orientation of the extracellular matrix together with cell determinants—including cell–cell and cell–matrix adhesion, cytoskeletal polarity and stiffness, and pericellular proteolysis—interdependently control migration mode and efficiency. Motile cells integrate variable inputs to adjust interactions among themselves and with the matrix to dictate the migration mode. The tuning model provides a matrix of parameters that control cell movement as an adaptive and interconvertible process with relevance to different physiological and pathological contexts.

Multi-nucleated giant cell formation from human cord blood monocytes in vitro, in comparison with adult peripheral blood monocytes

Multi-nucleated giant cells (MGCs; Langhans-type cell), formed from macrophage fusion, are recognized as a hallmark histological feature in chronic inflammation. However, their precise pathological role is still poorly understood, especially for microorganism pathogens in the neonatal immune system, which are capable of surviving intracellularly in phagocytes. To conduct a partial evaluation of the monocyte function of neonates, we investigated the ability of human cord blood monocytes to form MGCs in vitro by stimulating various cytokines and comparing them with adult peripheral blood monocytes. Monocytes from cord blood and adult peripheral blood were isolated and cultured for 14 days with cytokines known to induce MGC in vitro. The fusion index in experiments with a combination of interleukin (IL)-4 and macrophage colony-stimulating factor (M-CSF) and a combination of IL-4 and granulocyte-macrophage colony-stimulating factor (GM-CSF) was significantly lower in cord blood than in adult blood monocytes (P = 0.0018 and P = 0.0141, respectively). The number of nuclei per MGC was significantly lower in cord blood than in adult blood monocytes in experiments with IL-4 alone, the combination of IL-4 and M-CSF, and the combination of IL-4 and GM-CSF (P < 0.0001). These results suggest the possibility that the susceptibility of newborns to mycobacterium infection is due partly to impaired MGC formation.