Differential Thy-1 expression by splenic fibroblasts defines functionally distinct subsets

Single-cell computational machine learning approaches to immune-mediated inflammatory disease: New tools uncover novel fibroblast and macrophage interactions driving pathogenesis

Recent advances in single-cell sequencing technologies call for greater computational scalability and sensitivity to analytically decompose diseased tissues and expose meaningful biological relevance in individual cells with high resolution. And while fibroblasts, one of the most abundant cell types in tissues, were long thought to display relative homogeneity, recent analytical and technical advances in single-cell sequencing have exposed wide variation and sub-phenotypes of fibroblasts of potential and apparent clinical significance to inflammatory diseases. Alongside anticipated improvements in single cell spatial sequencing resolution, new computational biology techniques have formed the technical backbone when exploring fibroblast heterogeneity. More robust models are required, however. This review will summarize the key advancements in computational techniques that are being deployed to categorize fibroblast heterogeneity and their interaction with the myeloid compartments in specific biological and clinical contexts. First, typical machine-learning-aided methods such as dimensionality reduction, clustering, and trajectory inference, have exposed the role of fibroblast subpopulations in inflammatory disease pathologies. Second, these techniques, coupled with single-cell predicted computational methods have raised novel interactomes between fibroblasts and macrophages of potential clinical significance to many immune-mediated inflammatory diseases such as rheumatoid arthritis, ulcerative colitis, lupus, systemic sclerosis, and others. Third, recently developed scalable integrative methods have the potential to map cross-cell-type spatial interactions at the single-cell level while cross-tissue analysis with these models reveals shared biological mechanisms between disease contexts. Finally, these advanced computational omics approaches have the potential to be leveraged toward therapeutic strategies that target fibroblast-macrophage interactions in a wide variety of inflammatory diseases.

Plasma-derived extracellular vesicles from Plasmodium vivax patients signal spleen fibroblasts via NF-kB facilitating parasite cytoadherence

Plasmodium vivax is the most widely distributed human malaria parasite. Previous studies have shown that circulating microparticles during P. vivax acute attacks are indirectly associated with severity. Extracellular vesicles (EVs) are therefore major components of circulating plasma holding insights into pathological processes. Here, we demonstrate that plasma-derived EVs from Plasmodium vivax patients (PvEVs) are preferentially uptaken by human spleen fibroblasts (hSFs) as compared to the uptake of EVs from healthy individuals. Moreover, this uptake induces specific upregulation of ICAM-1 associated with the translocation of NF-kB to the nucleus. After this uptake, P. vivax-infected reticulocytes obtained from patients show specific adhesion properties to hSFs, reversed by inhibiting NF-kB translocation to the nucleus. Together, these data provide physiological EV-based insights into the mechanisms of human malaria pathology and support the existence of P. vivax-adherent parasite subpopulations in the microvasculature of the human spleen.

Extracellular vesicles (EVs) in plasma can affect pathogenesis of parasites, but details remain unclear. Here, Toda et al. characterize plasma-derived EVs from Plasmodium vivax patients and show that PvEVs are preferentially taken up by human spleen fibroblasts, facilitating parasite cytoadherence.

Lack of Thy1 defines a pathogenic fraction of cardiac fibroblasts in heart failure

In response to heart injury, inflammation, or mechanical overload, quiescent cardiac fibroblasts (CFs) can become activated myofibroblasts leading to pathological matrix remodeling and decline in cardiac function. Specific targeting of fibroblasts may thus enable new therapeutic strategies to delay or reverse the progression of heart failure and cardiac fibrosis. However, it remains unknown if all CFs are equally responsive to specific pathological insults and if there exist sub-populations of resident fibroblasts in the heart that have distinctive pathogenic phenotypes. Here, we show that in response to transverse aortic constriction (TAC)-induced heart failure, previously uncharacterized Thy1^neg (Thy1-/MEFSK4+/CD45-/CD31-) fraction of mouse ventricular fibroblasts became more abundant and attained a more activated, pro-fibrotic myofibroblast phenotype compared to Thy1^Pos fraction. In a tissue-engineered 3D co-culture model of healthy cardiomyocytes and freshly isolated CFs, Thy1^neg CFs from TAC hearts significantly decreased cardiomyocyte contractile function and calcium transient amplitude, and increased extracellular collagen deposition yielding a profibrotic heart tissue phenotype. In vivo, mice with global knockout of Thy1 developed more severe cardiac dysfunction and fibrosis in response to TAC-induced heart failure than wild-type mice. Taken together, our studies identify cardiac myofibroblasts lacking Thy1 as a pathogenic CF fraction in cardiac fibrosis and suggest important roles of Thy1 in pathophysiology of heart failure.

Functional genomics of stromal cells in chronic inflammatory diseases

PURPOSE OF REVIEW

Stroma is a broad term referring to the connective tissue matrix in which other cells reside. It is composed of diverse cell types with functions such as extracellular matrix maintenance, blood and lymph vessel development, and effector cell recruitment. The tissue microenvironment is determined by the molecular characteristics and relative abundances of different stromal cells such as fibroblasts, endothelial cells, pericytes, and mesenchymal precursor cells. Stromal cell heterogeneity is explained by embryonic developmental lineage, stages of differentiation to other cell types, and activation states. Interaction between immune and stromal cell types is critical to wound healing, cancer, and a wide range of inflammatory diseases. Here, we review recent studies of inflammatory diseases that use functional genomics and single-cell technologies to identify and characterize stromal cell types associated with pathogenesis.

RECENT FINDINGS

High dimensional strategies using mRNA sequencing, mass cytometry, and fluorescence activated cell-sorting with fresh primary tissue samples are producing detailed views of what is happening in diseased tissue in rheumatoid arthritis, inflammatory bowel disease, and cancer. Fibroblasts positive for CD90 (Thy-1) are enriched in the synovium of rheumatoid arthritis patients. Single-cell RNA-seq studies will lead to more discoveries about the stroma in the near future.

SUMMARY

Stromal cells form the microenvironment of inflamed and diseased tissues. Functional genomics is producing an increasingly detailed view of subsets of stromal cells with pathogenic functions in rheumatic diseases and cancer. Future genomics studies will discover disease mechanisms by perturbing molecular pathways with chemokines and therapies known to affect patient outcomes. Functional genomics studies with large sample sizes of patient tissues will identify patient subsets with different disease phenotypes or treatment responses.

Thy-1+/- fibroblast subsets in the human peritoneum

Fibrotic thickening of the peritoneum develops in patients receiving peritoneal dialysis (PD) for renal failure. For unknown reasons, however, in some patients it progresses to extensive fibrosis that compromises dialysis capacity of the peritoneum. It is increasingly clear that fibroblasts display large heterogeneity not only between but also within tissues. Differential surface expression of thymocyte differentiation antigen 1 (Thy-1) has been shown to identify functionally distinct fibroblast subsets in several organs. Here, we isolated Thy-1^+/- subsets of human peritoneal fibroblasts (HPFB) and analyzed them in terms of profibrotic myofibroblast features. In healthy individuals, Thy-1⁺ cells constituted ~45% of the HPFB population found in the greater omentum but were not detected in the parietal peritoneum. When propagated in culture and compared with Thy-1^- cells, omentum-derived Thy-1⁺ HPFB consistently displayed an increased expression of α-smooth muscle actin, collagen I, and transforming growth factor-β1. They also showed greater proliferation capacity and enhanced contractile properties. The number of Thy-1⁺ HPFB increased significantly in PD patients and made up more than 70 and 95% of all HPFB found in the omentum and parietal peritoneum, respectively. These data indicate that the expansion of Thy-1⁺ fibroblasts may contribute to fibrotic thickening of the peritoneal membrane during PD.

Immunological evaluation of an rsmD-like rRNA methyltransferase from Wolbachia endosymbiont of Brugia malayi

Wolbachia is a wonderful anti-filarial target with many of its enzymes and surface proteins (WSPs) representing potential drug targets and vaccine candidates. Here we report on the immunologic response of a drug target, rsmD-like rRNA methyltransferase from Wolbachia endosymbiont of Brugia malayi. The recombinant protein generated both humoral and cell-mediated response in BALB/c mice but compromised its immunity. The humoral response was transient and endured barely for six months in mice with or without B. Malayi challenge. In splenocytes of mice, the key humoral immunity mediating cytokine IL4 was lowered (IL4↓) while IFNγ, the major cytokine mediating cellular immunity was decreased along with upregulation of IL10 cytokine (IFNγ↓, IL10↑). The finding here indicates that the enzyme has low immunogenicity and triggers lowering of cytokine level in BALB/c mice. Interestingly the overall immune profile can be summed up with equivalent response generated by WSP or whole Wolbachia.

Nanobodies targeting mouse/human VCAM1 for the nuclear imaging of atherosclerotic lesions

RATIONALE

A noninvasive tool allowing the detection of vulnerable atherosclerotic plaques is highly needed. By combining nanomolar affinities and fast blood clearance, nanobodies represent potential radiotracers for cardiovascular molecular imaging. Vascular cell adhesion molecule-1 (VCAM1) constitutes a relevant target for molecular imaging of atherosclerotic lesions.

OBJECTIVE

We aimed to generate, radiolabel, and evaluate anti-VCAM1 nanobodies for noninvasive detection of atherosclerotic lesions.

METHODS AND RESULTS

Ten anti-VCAM1 nanobodies were generated, radiolabeled with technetium-99m, and screened in vitro on mouse and human recombinant VCAM1 proteins and endothelial cells and in vivo in apolipoprotein E-deficient (ApoE(-/-)) mice. A nontargeting control nanobody was used in all experiments to demonstrate specificity. All nanobodies displayed nanomolar affinities for murine VCAM1. Flow cytometry analyses using human human umbilical vein endothelial cells indicated murine and human VCAM1 cross-reactivity for 6 of 10 nanobodies. The lead compound cAbVCAM1-5 was cross-reactive for human VCAM1 and exhibited high lesion-to-control (4.95±0.85), lesion-to-heart (8.30±1.11), and lesion-to-blood ratios (4.32±0.48) (P<0.05 versus control C57Bl/6J mice). Aortic arch atherosclerotic lesions of ApoE(-/-) mice were successfully identified by single-photon emission computed tomography imaging. (99m)Tc-cAbVCAM1-5 binding specificity was demonstrated by in vivo competition experiments. Autoradiography and immunohistochemistry further confirmed cAbVCAM1-5 uptake in VCAM1-positive lesions.

CONCLUSIONS

The (99m)Tc-labeled, anti-VCAM1 nanobody cAbVCAM1-5 allowed noninvasive detection of VCAM1 expression and displayed mouse and human cross-reactivity. Therefore, this study demonstrates the potential of nanobodies as a new class of radiotracers for cardiovascular applications. The nanobody technology might evolve into an important research tool for targeted imaging of atherosclerotic lesions and has the potential for fast clinical translation.

Gene expression profiling in the skin of zebrafish infected with Citrobacter freundii

Skin is considered the largest immunologically active organ, but its molecular mechanism remains unclear in fish. Here, Affymetrix Zebrafish GeneChip was used to assess gene expression in the skin of zebrafish (Danio rerio) infected with the bacterium Citrobacter freundii. The results showed that 229 genes were differentially expressed, of which 196 genes were upregulated and 33 genes were downregulated. Gene Ontology and KEGG pathway analyses indicated 88 genes significantly associated with skin immunity involved in complement activation and acute phase response, defense and immune response, response to stress and stimulus, antigen processing and presentation, cell adhesion and migration, platelet activation and coagulation factors, regulation of autophagy and apoptosis. When compared with transcriptional profiles of previously reported carp (Cyprinus carpio) skin, a similar innate immunity (e.g., interferon, lectin, heat shock proteins, complements), and several different acute phase proteins (transferrin, ceruloplasmin, vitellogenin and alpha-1-microglobulin, etc.) were detected in zebrafish skin. The validity of the microarray results was verified by quantitative real-time PCR analysis of nine representative genes. This is first report that skin play important roles in innate immune responses to bacterial infection, which contribute to understanding the defense mechanisms of the skin in fish.

Strain-specific spleen remodelling in Plasmodium yoelii infections in Balb/c mice facilitates adherence and spleen macrophage-clearance escape

Knowledge of the dynamic features of the processes driven by malaria parasites in the spleen is lacking. To gain insight into the function and structure of the spleen in malaria, we have implemented intravital microscopy and magnetic resonance imaging of the mouse spleen in experimental infections with non-lethal (17X) and lethal (17XL) Plasmodium yoelii strains. Noticeably, there was higher parasite accumulation, reduced motility, loss of directionality, increased residence time and altered magnetic resonance only in the spleens of mice infected with 17X. Moreover, these differences were associated with the formation of a strain-specific induced spleen tissue barrier of fibroblastic origin, with red pulp macrophage-clearance evasion and with adherence of infected red blood cells to this barrier. Our data suggest that in this reticulocyte-prone non-lethal rodent malaria model, passage through the spleen is different from what is known in other Plasmodium species and open new avenues for functional/structural studies of this lymphoid organ in malaria.

Thy-1 attenuates TNF-alpha-activated gene expression in mouse embryonic fibroblasts via Src family kinase

Heterogeneous surface expression of Thy-1 in fibroblasts modulates inflammation and may thereby modulate injury and repair. As a paradigm, patients with idiopathic pulmonary fibrosis, a disease with pathologic features of chronic inflammation, demonstrate an absence of Thy-1 immunoreactivity within areas of fibrotic activity (fibroblast foci) in contrast to the predominant Thy-1 expressing fibroblasts in the normal lung. Likewise, Thy-1 deficient mice display more severe lung fibrosis in response to an inflammatory injury than wildtype littermates. We investigated the role of Thy-1 in the response of fibroblasts to the pro-inflammatory cytokine TNF-alpha. Our study demonstrates distinct profiles of TNF-alpha-activated gene expression in Thy-1 positive (Thy-1+) and negative (Thy-1-) subsets of mouse embryonic fibroblasts (MEF). TNF-alpha induced a robust activation of MMP-9, ICAM-1, and the IL-8 promoter driven reporter in Thy-1- MEFs, in contrast to only a modest increase in Thy-1+ counterparts. Consistently, ectopic expression of Thy-1 in Thy-1- MEFs significantly attenuated TNF-alpha-activated gene expression. Mechanistically, TNF-alpha activated Src family kinase (SFK) only in Thy-1- MEFs. Blockade of SFK activation abrogated TNF-alpha-activated gene expression in Thy-1- MEFs, whereas restoration of SFK activation rescued the TNF-alpha response in Thy-1+ MEFs. Our findings suggest that Thy-1 down-regulates TNF-alpha-activated gene expression via interfering with SFK- and NF-kappaB-mediated transactivation. The current study provides a novel mechanistic insight to the distinct roles of fibroblast Thy-1 subsets in inflammation.

Mast cell-derived prostaglandin D2 controls hyaluronan synthesis in human orbital fibroblasts via DP1 activation: implications for thyroid eye disease

Thyroid eye disease (TED) is a debilitating disorder characterized by the accumulation of adipocytes and hyaluronan (HA). Production of HA by fibroblasts leads to remarkable increases in tissue volume and to the anterior displacement of the eyes. Prostaglandin D(2) (PGD(2)), mainly produced by mast cells, promotes orbital fibroblast adipogenesis. The mechanism by which PGD(2) influences orbital fibroblasts and their synthesis of HA is poorly understood. We report here that mast cell-derived PGD(2) is a key factor that promotes HA biosynthesis by orbital fibroblasts. Primary orbital fibroblasts from TED patients were isolated and used to test the effects of PGD(2), prostaglandin J(2), as well as prostaglandin D receptor (DP) agonists and antagonists on HA synthesis. The expression of HA synthase (HAS), hyaluronidase, DP1, and DP2 mRNA levels was assessed by PCR. Small interfering RNAs against HAS1 or HAS2 were used to assess the importance of HAS isoforms on HA production. Treatment of human orbital fibroblasts with PGD(2) and PGJ(2) increased HA synthesis and HAS mRNA. HAS2 was the dominant isoform responsible for HA production by PGD(2). The effect of PGD(2) on HA production was mimicked by the selective DP1 agonist BW245C. The DP1 antagonist MK-0524 completely blocked PGD(2)-induced HA synthesis. Human mast cells (HMC-1) produced PGD(2). Co-culture of HMC-1 cells with orbital fibroblasts induced HA production and inhibition of mast cell-derived PGD(2) prevented HA synthesis. Mast cell-derived PGD(2) increased HA production via activation of DP1. Selectively targeting the production of PGD(2) and/or activation of DP1 may prevent pathological changes associated with TED.

Expression of mesenchymal stem cell marker CD90 on dermal sheath cells of the anagen hair follicle in canine species

The dermal sheath (DS) of the hair follicle is comprised by fibroblast-like cells and extends along the follicular epithelium, from the bulb up to the infundibulum. From this structure, cells with stem characteristics were isolated: they have a mesenchymal origin and express CD90 protein, a typical marker of mesenchymal stem cells. It is not yet really clear in which region of hair follicle these cells are located but some experimental evidence suggests that dermal stem cells are localized prevalently in the lower part of the anagen hair follicle. As there are no data available regarding DS stem cells in dog species, we carried out a morphological analysis of the hair follicle DS and performed both an immunohistochemical and an immunocytochemical investigation to identify CD90+ cells. We immunohistochemically evidenced a clear and abundant positivity to CD90 protein in the DS cells located in the lower part of anagen hair follicle. The positive cells showed a typical fibroblast-like morphology. They were flat and elongated and inserted among bundles of collagen fibres. The whole structure formed a close and continuous sleeve around the anagen hair follicle. Our immunocytochemical study allowed us to localize CD90 protein at the cytoplasmic membrane level.

Fibroblasts-a diverse population at the center of it all

The capacity of fibroblasts to produce and organize the extracellular matrix and to communicate with other cells makes them a central component of tissue biology. Even so, fibroblasts remain a somewhat enigmatic population. Our inability to fully comprehend these cells is in large part due to the paucity of unique cellular markers and to their pervasive diversity. Much of our understanding of fibroblast diversity has evolved from studies where subpopulations of these cells have been produced without resorting to cell surface markers. In this regard, cloning and mechanical separation of tissues prior to establishing cultures has provided multiple subpopulations. Nonetheless, in isolated situations, the expression or lack of expression of Thy-1/CD90 has been used to separate fibroblast subsets. The role of fibroblasts in intercellular communication is emerging through the implementation of organotypic studies in which three-dimensional fibroblast culture are combined with other populations of cells. Such studies have revealed critical paracrine loops that are essential for organ development and for wound repair. These studies also provide a backdrop for the emerging field of tissue engineering. The participation of fibroblasts in the regulation of tissue homeostasis and their contribution to the aging process are emerging issues that require better understanding. In short, fibroblasts represent a multifaceted, complex group of cells.

More Than Structural Cells, Fibroblasts Create and Orchestrate the Tumor Microenvironment

The tumor microenvironment comprises many cell types including infiltrating immune cells such as lymphocytes, endothelial cells and a complex stroma consisting mainly of fibroblasts. Fibroblasts are heterogeneous and consist of Thy-1+ and Thy-1- subsets that define different biosynthetic and differentiation potential. They produce mediators linked to carcinogenesis and metastasis, including Cox-2 and PGE2, both of which are also increased in most cancers. This review will highlight the emerging role of the complex fibroblastic stroma in establishing a microenvironment supporting malignant transformation, tumor growth and attenuation of host anti-tumor immune responses.

Evidence for enhanced Thy-1 (CD90) expression in orbital fibroblasts of patients with Graves' ophthalmopathy

BACKGROUND

Thy-1 is a surface protein that defines functionally distinct subpopulations of fibroblasts, with those lacking the antigen being capable of adipogenesis. Because increased fat cell development is a hallmark of the orbit in Graves' ophthalmopathy (GO), we wished to compare baseline Thy-1 expression in orbital fibroblasts from GO patients and normal individuals, and determine whether levels of the protein might be impacted by adipogenesis following peroxisome proliferator activator-gamma ligation.

METHODS

Orbital adipose/connective tissue specimens were obtained from euthyroid patients undergoing orbital decompression surgery for severe GO (n = 9) and from normal individuals (n = 9). Thy-1 mRNA and protein levels were assessed in tissue specimens and in orbital fibroblast cultures at baseline using RT-PCR, quantitative immunofluorescent staining, and flow cytometry using a specific Thy-1 mouse anti-human CD90/Thy-1 monoclonal antibody. In addition, some orbital fibroblast cultures were treated with rosiglitazone (1 microL/mL; 2 nM) or control for 10 days in culture.

RESULTS

We found that Thy-1 mRNA and protein expression was higher in uncultured GO connective/adipose tissue specimens (3.8-fold; 0.835 +/- 0.116 relative expression) compared with normal (0.22 +/- 0.062; p = 0.002) and in cultured orbital fibroblasts from GO patients (3.3-fold; 9.28 +/- 1.82 relative expression) compared with normal cultures (2.80 +/- 0.42; p = 0.013). Adipocyte differentiation had no effect on Thy-1 expression. Flow cytometry and immunofluorescent staining showed increased numbers of Thy-1-positive cells in the GO (mean 77.9 + 4.09%; range 66.5-84.8%) compared with the normal fibroblast cultures (66.8 + 1.6%; range 63.3-71.0% positive; p = 0.046), as well as higher levels of expression on the positive cells.

CONCLUSIONS

Increased Thy-1 expression in GO orbital tissues and cultures is likely a consequence of the orbital disease process, reflecting both the presence of increased numbers of Thy-1-positive cells and higher expression on those cells. Adipogenesis itself does not appear to impact Thy-1 expression. Increased expression of this protein in GO could represent an adaptive response to cell injury, in effect limiting disease progression within the orbital adipose/connective tissues.

Deep dermal fibroblasts contribute to hypertrophic scarring

Hypertrophic scar (HTS) following thermal injury is a dermal fibroproliferative disorder that leads to considerable morbidity. The development of HTS involves numerous cell types and cytokines with dermal fibroblasts being a key cell. We have previously reported that the phenotype of fibroblasts isolated from HTS was altered compared to fibroblasts from normal skin. In this study, normal skin was horizontally sectioned into five layers using a dermatome from which fibroblasts were isolated and cultured. Cells from the deeper layers were observed to proliferate at a slow rate, but were morphologically larger. In ELISA and FACS assays, cells from the deeper layers produced more TGF-beta1 and TGF-beta1 producing cells were higher. In quantitative RT-PCR, the cells from the deeper layers had higher CTGF and HSP47 mRNA levels compared to those from superficial layers. In western blot, FACS and collagen gel assays, fibroblasts from the deeper layers produced more alpha-smooth muscle actin (alpha-SMA), had higher alpha-SMA positive cells and contracted collagen gels more. Fibroblasts from the deeper layers were also found to produce more collagen, but less collagenase by mass spectrometry and collagenase assay. Interestingly, cells from the deeper layers also produced more of the proteoglycan, versican, but less decorin. Taken together, these data strongly demonstrate that fibroblasts from the deeper layers of the dermis resemble HTS fibroblasts, suggesting that the deeper layer fibroblasts may be critical in the formation of HTS.

P2Y2 nucleotide receptor activation up-regulates vascular cell adhesion molecule-1 [corrected] expression and enhances lymphocyte adherence to a human submandibular gland cell line

Sjögren's syndrome (SS) is a chronic inflammatory autoimmune disease that causes salivary and lacrimal gland tissue destruction resulting in impaired secretory function. Although lymphocytic infiltration of salivary epithelium is associated with SS, the mechanisms involved have not been adequately elucidated. Our previous studies have shown that the G protein-coupled P2Y2 nucleotide receptor (P2Y2R) is up-regulated in response to damage or stress of salivary gland epithelium, and in salivary glands of the NOD.B10 mouse model of SS-like autoimmune exocrinopathy. Additionally, we have shown that P2Y2R activation up-regulates vascular cell adhesion molecule-1 (VCAM-1) expression in endothelial cells leading to the binding of monocytes. The present study demonstrates that activation of the P2Y2R in dispersed cell aggregates from rat submandibular gland (SMG) and in human submandibular gland ductal cells (HSG) up-regulates the expression of VCAM-1. Furthermore, P2Y2R activation mediated the up-regulation of VCAM-1 expression in HSG cells leading to increased adherence of lymphocytic cells. Inhibitors of EGFR phosphorylation and metalloprotease activity abolished P2Y2R-mediated VCAM-1 expression and decreased lymphocyte binding to HSG cells. Moreover, silencing of EGFR expression abolished UTP-induced VCAM-1 up-regulation in HSG cells. These results suggest that P2Y2R activation in salivary gland cells increases the EGFR-dependent expression of VCAM-1 and the binding of lymphocytes, a pathway relevant to inflammation associated with SS.

Characterization of human lung tumor-associated fibroblasts and their ability to modulate the activation of tumor-associated T cells

The tumor microenvironment of human non-small cell lung cancer (NSCLC) is composed largely of stromal cells, including fibroblasts, yet these cells have been the focus of few studies. In this study, we established stromal cell cultures from primary NSCLC through isolation of adherent cells. Characterization of these cells by flow cytometry demonstrated a population which expressed a human fibroblast-specific 112-kDa surface molecule, Thy1, alpha-smooth muscle actin, and fibroblast activation protein, but failed to express CD45 and CD11b, a phenotype consistent with that of an activated myofibroblast. A subset of the tumor-associated fibroblasts (TAF) was found to express B7H1 (PD-L1) and B7DC (PD-L2) constitutively, and this expression was up-regulated by IFN-gamma. Production of cytokines and chemokines, including IFN-gamma, monokine induced by IFN-gamma, IFN-gamma-inducible protein-10, RANTES, and TGF-beta1 was also demonstrated in these cells. Together, these characteristics provide multiple opportunities for the TAF to influence cellular interactions within the tumor microenvironment. To evaluate the ability of TAF to modulate tumor-associated T cell (TAT) activation, we conducted coculture experiments between autologous TAF and TAT. In five of eight tumors, TAF elicited a contact-dependent enhancement of TAT activation, even in the presence of a TGF-beta1-mediated suppressive effect. In the three other tumors, TAF had a net suppressive effect upon TAT activation, and, in one of these cases, blockade of B7H1 or B7DC was able to completely abrogate the TAF-mediated suppression. We conclude that TAF in human NSCLC are functionally and phenotypically heterogeneous and provide multiple complex regulatory signals that have the potential to enhance or suppress TAT function in the tumor microenvironment.

Thy-1, a versatile modulator of signaling affecting cellular adhesion, proliferation, survival, and cytokine/growth factor responses

Thy-1 is a 25-37 kDa glycosylphosphatidylinositol (GPI)-anchored protein involved in T cell activation, neurite outgrowth, apoptosis, tumor suppression, wound healing, and fibrosis. To mediate these diverse effects, Thy-1 participates in multiple signaling cascades. In this review, we discuss Thy-1 signaling primarily in non-immunologic cell types, including neurons, mesangial cells, ovarian cancer cells, nasopharyngeal carcinoma cells, endothelial cells, and fibroblasts. We review the current literature regarding Thy-1 signaling via integrins, protein tyrosine kinases, and cytokines and growth factors; and the roles of these signaling pathways in cellular adhesion, apoptosis, cell proliferation, and cell adhesion and migration. We also discuss the role of Thy-1 localization to lipid rafts, and of the GPI anchor in Thy-1 signaling. Ongoing research on the mechanisms of Thy-1 signaling will add to our understanding of the diverse physiologic and pathologic processes in which Thy-1 plays a role.

Thy-1 as a regulator of cell-cell and cell-matrix interactions in axon regeneration, apoptosis, adhesion, migration, cancer, and fibrosis

Thy-1 (CD90) is a 25-37 kDa glycosylphosphatidylinositol (GPI) -anchored glycoprotein expressed on many cell types, including T cells, thymocytes, neurons, endothelial cells, and fibroblasts. Activation of Thy-1 can promote T cell activation, and this role of Thy-1 is reviewed elsewhere. Thy-1 also affects numerous nonimmunologic biological processes, including cellular adhesion, neurite outgrowth, tumor growth, migration, and cell death. In reviewing the nonimmunologic functions of Thy-1, we discuss the phenotype of the Thy-1 null mouse, signaling pathways modulated by Thy-1, the role of the GPI anchor in Thy-1 localization to lipid rafts and signaling, and regulation of Thy-1 expression. Thy-1 is an important regulator of cell-cell and cell-matrix interactions, with important roles in nerve regeneration, metastasis, inflammation, and fibrosis.

Contrasting Roles for Domain 4 of VCAM-1 in the Regulation of Cell Adhesion and Soluble VCAM-1 Binding to Integrin α4β1

Cell adhesion mediated by the interaction between integrin alpha4beta1 and VCAM-1 is important in normal physiologic processes and in inflammatory and autoimmune disease. Numerous studies have mapped the alpha4beta1 binding sites in VCAM-1 that mediate cell adhesion; however, little is known about the regions in VCAM-1 important for regulating soluble binding. In the present study, we demonstrate that 6D VCAM-1 (an alternatively spliced isoform of VCAM-1 lacking Ig-like domain 4) binds alpha4beta1 with a higher relative affinity than does the full-length form of VCAM-1 containing 7 Ig-like extracellular domains (7D VCAM-1). In indirect binding assays, the EC50 of soluble 6D VCAM-1 binding to alpha4beta1 on Jurkat cells (in 1 mM MnCl2) was 2 x 10(-9) M, compared with 7D VCAM-1 at 11 x 10(-9) M. When used in solution to inhibit alpha4beta1 mediated cell adhesion, the IC50 of 6D VCAM-1 was 13 x 10(-9) M, compared with 7D VCAM-1 measured at 150 x 10(-9) M. Removal of Ig-like domains 4, 5, or 6, or simply substituting Asp328 in domain 4 of 7D VCAM-1 with alanine, caused increased binding of soluble 7D VCAM-1 to alpha4beta1. In contrast, cells adhered more avidly to 7D VCAM-1 under shear force, as it induced cell spreading at lower concentrations than did 6D VCAM-1. Finally, soluble 6D VCAM-1 acts as an agonist through alpha4beta1 by augmenting cell migration and inducing cell aggregation. These results indicate that the domain 4 of VCAM-1 plays a contrasting role when VCAM-1 is presented in solution or as a cell surface-expressed adhesive substrate.

Loss of fibroblast Thy-1 expression correlates with lung fibrogenesis

Fibroblasts consist of heterogeneous subpopulations that have distinct roles in fibrotic responses. Previously we reported enhanced proliferation in response to fibrogenic growth factors and selective activation of latent transforming growth factor (TGF)-beta in fibroblasts lacking cell surface expression of Thy-1 glycoprotein, suggesting that Thy-1 modulates the fibrogenic potential of fibroblasts. Here we report that compared to controls Thy-1-/- C57BL/6 mice displayed more severe histopathological lung fibrosis, greater accumulation of lung collagen, and increased TGF-beta activation in the lungs 14 days after intratracheal bleomycin. The majority of cells demonstrating TGF-beta activation and myofibroblast differentiation in bleomycin-induced lesions were Thy-1-negative. Histological sections from patients with idiopathic pulmonary fibrosis demonstrated absent Thy-1 staining within fibroblastic foci. Normal lung fibroblasts, in both mice and humans, were predominantly Thy-1-positive. The fibrogenic cytokines interleukin-1 and tumor necrosis factor-alpha induced loss of fibroblast Thy-1 surface expression in vitro, which was associated with Thy-1 shedding, Smad phosphorylation, and myofibroblast differentiation. These results suggest that fibrogenic injury promotes loss of lung fibroblast Thy-1 expression, resulting in enhanced fibrogenesis.

Insights into the role of fibroblasts in human autoimmune diseases

Traditional wisdom has considered fibroblasts as contributing to the structural integrity of tissues rather than playing a dynamic role in physiological or pathological processes. It is only recently that they have been recognized as comprising diverse populations of cells exhibiting complex patterns of biosynthetic activity. They represent determinants that react to stimuli and help define tissue remodelling through the expression of molecules imposing constraints on their cellular neighbourhood. Moreover, fibroblasts can initiate the earliest molecular events leading to inflammatory responses. Thus they must now be viewed as active participants in tissue reactivity. In this short review, I will provide an overview of contemporary thought about the contribution of fibroblasts to the pathogenesis of autoimmune processes through their expression of, and responses to, mediators of inflammation and tissue remodelling.

Shared expression of phenotypic markers in systemic sclerosis indicates a convergence of pericytes and fibroblasts to a myofibroblast lineage in fibrosis

The mechanisms by which microvascular damage leads to dermal fibrosis in diffuse cutaneous systemic sclerosis (dcSSc) are unclear. We hypothesized that microvascular pericytes constitute a cellular link between microvascular damage and fibrosis by transdifferentiating into myofibroblasts. We used a combination of immunohistochemistry and double immunofluorescence labelling of frozen skin biopsies taken from normal and dcSSc patients to determine whether a phenotypic link between pericytes and myofibroblasts exists in dcSSc. Using α-smooth muscle actin, the ED-A splice variant of fibronectin (ED-A FN) and Thy-1 to identify myofibroblasts, we demonstrated the presence of myofibroblasts in fibrotic dcSSc skin. Myofibroblasts were totally absent from control skin, atrophic stage dcSSc skin and non-lesional skin. Using double immunofluorescence labelling, both myofibroblasts and pericytes were shown to express ED-A FN and Thy-1 in dcSSc skin but not in control skin. Proliferating cell nuclear antigen was also expressed by myofibroblasts and pericytes in dcSSc skin while being absent in control skin. These observations suggest that the presence of myofibroblasts may represent a transitional phase during the fibrotic stages of dcSSc and that Thy-1^+ve pericytes participate in the fibrogenic development of dcSSc by synthesizing ED-A FN, which may be associated with a proliferation and transition of pericytes and fibroblasts to myofibroblasts, thus linking microvascular damage and fibrosis.

Lung fibroblast clones from normal and fibrotic subjects differ in hyaluronan and decorin production and rate of proliferation

Development of fibrosis involves an increase in the deposition of connective tissue components including collagens, fibronectin and proteoglycans. One hypothesis to account for matrix deposition in fibrosis is that fibroblast with differing matrix producing capacity are involved in the fibrotic process. To test this hypothesis, primary fibroblast cultures and clones derived from these primary lines were established from the lung tissue of control patients and patients with pulmonary fibrosis. The primary lines and derived clones were studied in relation to their capacity to proliferate and to produce proteoglycans and hyaluronan. Primary fibroblast cultures and clones from normal subjects and patients with lung fibrosis differed considerably, with up to 13-fold difference, in both hyaluronan and proteoglycan production. The major proteoglycan produced was decorin in both controls and cultures from fibrotic patients, while cultures from patients with lung fibrosis had a higher expression of mRNA for both collagen and decorin. Clones derived from a primary line from a fibrotic patient secreted 3-fold greater amounts of decorin than those from a control subject. Furthermore, a negative correlation between proliferation and synthesis of decorin was noted. We suggest that different fibroblast clones accumulate in the lung, and that specific cell populations of high decorin producing fibroblasts may exist which are crucial in the pathogenesis of fibrosis.

Thrombospondin-1-induced focal adhesion disassembly in fibroblasts requires Thy-1 surface expression, lipid raft integrity, and Src activation

The hep I peptide of thrombospondin-1 is known to induce the disassembly of focal adhesions, a critical step in regulating cellular adhesive changes needed for cell motility. Fibroblasts that are heterogeneous with respect to the surface expression of Thy-1 differ markedly in morphology, cytoskeletal organization, and migration, suggesting differential regulation of focal adhesion dynamics. Here we demonstrate that disassembly of focal adhesions mediated by both full-length thrombospondin-1 and the hep I peptide in fibroblasts requires the expression of Thy-1, although it does not appear to function as a stable member of the hep I receptor complex. Consistent with a known function of Thy-1 in regulating lipid raft-associated signaling, intact lipid rafts are necessary for hep I-mediated focal adhesion disassembly. Furthermore, we establish Src family kinase (SFK) activation as a novel component required for hep I-induced signaling leading to focal adhesion disassembly. hep I induces transient phosphorylation of SFKs in Thy-1-expressing fibroblasts only. Therefore, we conclude that Thy-1 surface expression is required for thrombospondin-1-induced focal adhesion disassembly in fibroblasts through an SFK-dependent mechanism. This represents a novel role for Thy-1 in the regulation of fibroblast-matrix interactions critical to tissue homeostasis and remodeling.

Thy-1 expression in human fibroblast subsets defines myofibroblastic or lipofibroblastic phenotypes

Fibroblasts represent a dynamic population of cells, exhibiting functional heterogeneity within and among tissues. Fibroblast heterogeneity also results from phenotypic differences and may arise from activation or differentiation processes taking place in the cells. We previously reported that human fibroblasts were heterogeneous with respect to surface Thy-1 expression and that separation into Thy-1(+) and Thy-1(-) subsets resulted in functionally distinct subpopulations, leading to the concept of fibroblast subset specialization. In this report we investigated whether Thy-1(+) and/or Thy-1(-) fibroblasts were capable of differentiating into myofibroblasts or lipofibroblasts. Fibroblast subsets were used from human myometrium and orbit to test this hypothesis. Only Thy-1(+) human myometrial and orbital fibroblasts were capable of myofibroblast differentiation after treatment with TGFbeta or platelet concentrate supernatant, assessed by alpha smooth muscle actin expression. Interestingly, only Thy-1(-), but not Thy-1(+) subsets differentiated to lipofibroblasts, as determined by the accumulation of cytoplasmic lipid droplets after treatment with 15-deoxy-Delta(12, 14)-PGJ(2) or ciglitazone. We propose that fibroblast Thy-1 display pre-determines lineage to a contractile or lipid-like phenotype in the human myometrium and orbit. This additional distinction between Thy-1(+) and Thy-1(-) human fibroblast subtypes has important consequences in normal tissue homeostasis and in pathogenesis of orbital and myometrial diseases characterized by persistent myofibroblasts or fat accumulation, such as occurs in Graves' ophthalmopathy, tissue fibrosis, abnormal wound healing, and scarring.

Establishment of mouse embryonic fibroblast cell lines that promote ex vivo expansion of human cord blood CD34+ hematopoietic progenitors

The development of culture systems that facilitate ex vivo maintenance and expansion of transplantable hematopoietic progenitor cells (HPC) is vital to stem cell transplantation. The use of a monolayer of stromal cells on which to grow HPC in direct contact allows high efficiency ex vivo expansion of HPC. Here, we report an establishment of three murine embryonic fibroblast stromal cell lines from adherent cells of day-12 mouse embryos. Among them, HYMEQ-5 was most efficient in supporting long-term maintenance of human umbilical cord blood (CB) CD34(+) cells. Human CB CD34(+) cells cultured on HYMEQ-5 in the presence of stem cell factor (SCF), thrombopoietin, and flk-ligand (FL) showed high expansion of CD34(+)CD38(-) cells and highly proliferative potential-colony forming cells (HPP-CFC). Direct cell-to-cell contact between CD34(+) cells and HYMEQ-5 was important for this expansion. RT-PCR analysis showed that HYMEQ-5 produced FL, SCF, interleukin-6, and macrophage colony-stimulating factor (M-CSF). Expanded CB CD34(+) cells efficiently reconstituted hematopoiesis in nonobese diabetic/severe combined immunodeficient disease (NOD/SCID) mice. These findings suggest that HYMEQ-5 provides a milieu that supports long-term human hematopoiesis as well as ex vivo expansion of human CB CD34(+) HPC. This cell line may facilitate elucidation of the mechanism of cellular interactions between HPC and stromal cells.

Differential COX localization and PG release in Thy-1(+) and Thy-1(-) human female reproductive tract fibroblasts

A key role exists for prostaglandins (PGs) in reproductive health, including fertility and parturition. However, the cellular sources and regulation of PG production by cyclooxygenase (COX) in the human female reproductive tract remain poorly understood. We recently reported that human female reproductive tract fibroblasts are divisible into distinct subsets based on their Thy-1 surface expression. Herein, we demonstrate that the expression, induction, and subcellular localization of COX-1 and COX-2 and the downstream PG biosynthesis are markedly different between these subsets. Specifically, Thy-1(+) fibroblasts highly express COX-1, which is responsible for high-level PGE(2) production, a feature usually attributed to the COX-2 isoenzyme. In contrast, COX-2, generally considered an inducible isoform, is constitutively expressed in the Thy-1(-) subset, which only minimally produces PGE(2). The intracellular signaling pathways for COX regulation also differ between the subsets. Determination of differences in signal transduction, COX expression and localization, and PG production by human reproductive fibroblast subtypes supports the concept of fibroblast heterogeneity and the possibility that these subsets may play unique roles in tissue homeostasis and in inflammation.

Fibroblast subsets in the human orbit: Thy-1+ and Thy-1- subpopulations exhibit distinct phenotypes

An emerging concept is that fibroblasts are not homogeneous, but rather consist of subsets, capable of producing regulatory mediators that control regional inflammatory responses. Fibroblasts are key effector cells in Graves' ophthalmopathy, responsible for the connective tissue remodeling, and are a rich source of inflammatory mediators. The purpose of this research was to characterize subsets of the fibroblasts in the human orbit. The strategy used was to define fibroblast subpopulations based on surface expression of the Thy-1 antigen. Fibroblast strains derived from human orbital connective tissue exhibit heterogeneous Thy-1 expression. We show, for the first time, separation of orbital fibroblasts into functionally distinct Thy-1+ and Thy-1- subsets using magnetic beading techniques. Both subsets produced the pro-inflammatory cytokine interleukin-6 (IL-6) after stimulation with IL-1beta or the CD40 pathway, whereas Thy-1+ fibroblasts produced higher levels of prostaglandin endoperoxide H synthase-2 (PGHS-2) and prostaglandin E2 (PGE(2)). Thy-1- fibroblasts produced more IL-8 than Thy-1+ fibroblasts, and when treated with interferon-gamma (IFN-gamma) up-regulated MHC class II expression more robustly. Furthermore, CD40 was expressed in a bimodal distribution within each fibroblast subset. These observations suggest that fibroblast subsets in the human orbit play distinct roles in the regulation of immune and inflammatory responses crucial in the initiation and development of thyroid-associated ophthalmopathy.

Phenotypic identification and development of distinct microvascular compartments in the postnatal mouse spleen

In this paper we report the development of the sinus network of mouse spleen during the first postnatal month as studied with a set of new rat monoclonal antibodies (mAbs) against mouse splenic endothelial cell subpopulations. One of the new mAbs (IBL-7/1) also stained B-cell lineage cells in the spleen shortly after the birth as confirmed by three-color flow cytometry. This B-cell staining in the primordial follicles vanished by the fourth postnatal week, so that the expression of IBL-7/1 antigen was restricted to the marginal sinus endothelium and some red pulp sinuses and a minor B-cell subset in the spleen, presumably distinct from the follicular B-cell compartment. The other mAb (IBL-9/2) selectively labeled the sinusoids of the deeper part of the red pulp, without any reactivity against hemopoietic cells. The IBL-9/2-reactive cells in newborns appeared as isolated elements throughout spleen, and during the segregation of white and red pulps they formed an extensive network in the red pulp outside the marginal zone. Double-labeling immunofluorescence revealed that most of these sinusoids also stained weakly with IBL-7/1 mAb, whereas the strongly IBL-7/1-positive vessels of this region were IBL-9/2 negative. Neither of these mAbs reacted with the central artery. The comparative phenotypic analysis of the various vascular segments indicates that the splenic sinusoids of the marginal zone and red pulp, respectively, are lined with a heterogeneous array of endothelium. For the precise identification, isolation, and characterization of the possible homing function of these endothelium subsets these region-specific mAbs may be of potential value.

Fibroblast heterogeneity: existence of functionally distinct Thy 1(+) and Thy 1(-) human female reproductive tract fibroblasts

Little is known about fibroblasts from the female reproductive tract, much less whether or not functional subsets exist. Fibroblasts are key as sentinel cells for recruiting white blood cells and for wound healing. The purpose of this research was to evaluate the possibility that functional subsets of fibroblasts exist in the human female reproductive tract. The strategy used was to define fibroblast subpopulations based on their surface expression of the Thy 1 antigen. In situ staining of human myometrium and endometrium showed heterogeneous staining for Thy 1. Freshly derived strains of fibroblasts from the myometrium and endometrium also demonstrated heterogeneous Thy 1 expression. For the first time, using magnetic beading and fluorescence-activated cell sorting, human myometrial fibroblasts were successfully separated into functionally unique Thy 1(+) and Thy 1(-) subsets. Both subsets produced the proinflammatory cytokines interleukin (IL)-6 and IL-8 after IL-1beta stimulation, but only the Thy 1(+) subset produced MCP-1. Furthermore, only Thy 1(+) fibroblasts up-regulated CD40 surface expression with IL-1beta or interferon-gamma treatment. Engagement of CD40 in the Thy 1(+) subpopulation induced IL-6, IL-8, and MCP-1. The discovery of functional subsets of reproductive tract fibroblasts now permits assessment of their roles in the normal functions of the reproductive tract and in disease states such as adhesions and menorrhagia.

Regulation of cytokine production in human gingival fibroblasts following treatment with nicotine and lipopolysaccharide

BACKGROUND

Patients who smoke are at increased risk for chronic periodontitis (CP). Most studies suggest that the microbial flora in these patients is similar to that found in non-smoking CP patients. Thus, the increased risk for development of CP is not dependent on an altered microbial profile, but rather to some change in the host response to these periopathogens. There is evidence that human gingival fibroblasts (HGF) derived from diseased sites produce greater amounts of interleukin (IL)-6 and IL-8 in vitro than cells derived from healthy sites. This suggests that HGF subpopulations may be selected based upon the inflammatory milieu in which they reside. The hypothesis to be tested was that the combination of nicotine and lipopolysaccharide (LPS) could regulate HGF inflammatory mediator production.

METHODS

HGF cell cultures were established from explants derived from 10 patients with CP. HGF cell cultures were stimulated with 1 mM, 1 microM, or 1 nM nicotine +/- Escherichia coli or Porphyromonas gingivalis LPS. At 12, 24, or 48-hour time points, the cells were counted and the supernatant was collected for subsequent IL-6 and IL-8 determination in an enzyme-linked immunosorbent assay.

RESULTS

At the 24-hour time point, 1 nM nicotine stimulated IL-6 production compared to control (P=0.02). E. coli LPS alone caused a 3- to 4-fold increase in IL-6 and IL-8 production, whereas P gingivalis LPS did not augment IL-6 or IL-8. A synergistic effect upregulating IL-6 was observed with combined treatment of 1 mM nicotine and E. coli LPS or P gingivalis LPS at the 24-hour time point (P<0.0005 and P=0.002, respectively). Similar effects were seen when IL-8 production was evaluated following HGF stimulation with high doses of nicotine and E. coli LPS or P gingivalis LPS.

CONCLUSIONS

These results demonstrate that nicotine by itself can stimulate HGF IL-6 and IL-8 production. Moreover, the combination of high doses of nicotine and either E. coli or P gingivalis LPS can synergistically upregulate cytokine production. These findings support the hypothesis that a proinflammatory fibroblast phenotype may be elicited in an environment enriched with bacterial LPS and nicotine.

Conditional vascular cell adhesion molecule 1 deletion in mice: impaired lymphocyte migration to bone marrow

We generated vascular cell adhesion molecule (VCAM)-1 "knock-in" mice and Cre recombinase transgenic mice to delete the VCAM-1 gene (vcam-1) in whole mice, thereby overcoming the embryonic lethality seen with conventional vcam-1-deficient mice. vcam-1 knock-in mice expressed normal levels of VCAM-1 but showed loss of VCAM-1 on endothelial and hematopoietic cells when interbred with a "TIE2Cre" transgene. Analysis of peripheral blood from conditional vcam-1-deficient mice revealed mild leukocytosis, including elevated immature B cell numbers. Conversely, the bone marrow (BM) had reduced immature B cell numbers, but normal numbers of pro-B cells. vcam-1-deficient mice also had reduced mature IgD+ B and T cells in BM and a greatly reduced capacity to support short-term migration of transferred B cells, CD4+ T cells, CD8+ T cells, and preactivated CD4+ T cells to the BM. Thus, we report an until now unappreciated dominant role for VCAM-1 in lymphocyte homing to BM.

Isolation and characterization of rheumatoid arthritis synovial fibroblasts from primary culture--primary culture cells markedly differ from fourth-passage cells

To reduce culture artifacts by conventional repeated passaging and long-term culture in vitro, the isolation of synovial fibroblasts (SFB) was attempted from rheumatoid arthritis (RA) synovial membranes by trypsin/collagenase digest, short-term in vitro adherence (7 days), and negative isolation using magnetobead-coupled anti-CD14 monoclonal antibodies. This method yielded highly enriched SFB (85% prolyl-4-hydroxylase+/74% Thy-1/CD90+ cells; <2% contaminating macrophages; <1% leukocytes/endothelial cells) that, in comparison with conventional fourth-passage RA-SFB, showed a markedly different phenotype and significantly lower proliferation rates upon stimulation with platelet-derived growth factor and IL-1beta. This isolation method is simple and reliable, and may yield cells with features closer to the in vivo configuration of RA-SFB by avoiding extended in vitro culture.

Regulation of gingival fibroblast interleukin-6 secretion by cyclosporine A

BACKGROUND

Cyclosporine A (CsA) is a widely used immunosuppressant, with clinical applications ranging from organ transplants to chronic inflammatory diseases. One of the side effects associated with CsA treatment is the development of gingival overgrowth. Exuberant growth of connective tissue within the periodontium can result from hyperactivity of resident fibroblasts. Fibroblasts are capable of secreting interleukin-6 (IL-6), which has been shown to enhance proliferation as well as collagen and glycosaminoglycan synthesis by these cells. We tested the hypothesis that one of the pathogenetic mechanisms underlying CsA-induced fibrosis is an enhanced IL-6 secretion by gingival fibroblasts (GF) in response to this drug.

METHODS

The ability of CsA to upregulate GF IL-6 secretion alone or in combination with bacterial challenge or other inflammatory cytokines was tested in an in vitro system. Fibroblast cultures were established from systemically healthy gingival tissue donors and were challenged with CsA in the absence or presence of bacteria, IL-1beta, or tumor necrosis factor (TNF) alpha as co-stimulants. Nifedipine and phenytoin were also tested to further support findings with CsA. After 72 hours of incubation, culture supernatants were collected and analyzed for IL-6 content by ELISA.

RESULTS

We have shown that GF respond to CsA with an increase in IL-6 secretion. The magnitude of this response varies among cultures derived from different tissue donors. We have also demonstrated that GF IL-6 responses to bacterial challenge or TNFalpha are downregulated by CsA. However, CsA synergizes with IL-1beta to further upregulate IL-6 secretion, and this effect is shared by phenytoin and nifedipine.

CONCLUSIONS

We conclude that one of the pathogenetic mechanisms underlying drug-induced gingival overgrowth may be enhanced secretion of IL-6 by GF in response to these medications. This is the first report on direct and indirect effects of gingival overgrowth-related medications on GF IL-6 metabolism. This work will lay the foundation for future studies directed towards the development of prevention or treatment modalities for gingival overgrowth based on blocking the fibrogenic activities of IL-6 at the cellular level.

Fibroblast-Secreted Macrophage Colony-Stimulating Factor Is Responsible for Generation of Biphenotypic B/Macrophage Cells from a Subset of Mouse B Lymphocytes

Normal and malignant CD5+ B lymphocytes can develop macrophage-like characteristics. One stimulus of this phenotypic shift is culture of normal mouse splenic B lymphocytes with splenic fibroblasts or their conditioned media. These biphenotypic B/macrophage (B/Mφ) cells simultaneously display macrophage characteristics, such as phagocytosis and F4/80 expression, while retaining B cell features, including expression of surface Ig, CD5, B220, and rearranged Ig genes. The present study investigated the fibroblast-secreted factor that promotes this phenotypic change from B cell to B/Mφ cell. RT-PCR analysis demonstrated that mRNA for M-CSF is produced by splenic fibroblasts. Recombinant M-CSF (CSF-1) could replace fibroblast-conditioned medium to elicit the development and survival of B/Mφ cells from splenic B lymphocytes. In addition, neutralization of fibroblast-secreted M-CSF with specific mAbs abrogated the ability of conditioned supernatants to promote outgrowth of B/Mφ cells. The transition from B lymphocyte to B/Mφ cell was marked by the kinetic appearance of mRNA for the M-CSF receptor, c-fms, at day 3 following culture initiation. These results demonstrate that M-CSF is important in the development and physiology of mouse B/Mφ cells and potentially in the growth of human biphenotypic hematological malignancies. Interestingly, the presence of IFN-γ in splenic B lymphocyte cultures abrogated the effect of fibroblast-conditioned medium or M-CSF on outgrowth of B/Mφ cells. Furthermore, these findings suggest that a Th1 microenvironment favored by typical macrophages is detrimental to the outgrowth of B/Mφ cells.

Peripheral nerve fibroblasts as a source of IL-6, TNFalpha and IL-1 and their modulation by IFNgamma

Interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha), and interleukin-1 (IL-1) are immunomodulatory cytokines produced by Schwann cells of the peripheral nervous system (PNS). Their upregulation has been associated with autoimmune inflammatory diseases of the PNS such as Guillain-Barré Syndrome (GBS) and Chronic Inflammatory Demyelinating Neuropathy (CIDP). We now report that PNS fibroblasts and a PNS fibroblast cell line - MA-1 express mRNA for IL-6, TNFalpha and IL-I and that the MA-1 cell line secretes these molecules. Flow cytometry and fluorescent activated cell sorting defined that 76% of MA-1 fibroblasts were Thy1.1+ and 24% were Thy1.1-. Each subset expressed major histocompatibility class (MHC) I molecules and intercellular adhesion molecule-1 (ICAM-1). IFNgamma stimulation induced the expression of MHC II molecules in Thy1.1+, but not Thy1.1(-) cells. All MA-1 cells expressed mRNA for IL-6, TNFalpha, and IL-1 plus or minus IFNgamma stimulation. IFNgamma stimulation significantly reduced the production of IL-6 but increased TNFalpha production. Direct in situ reverse-transcriptase polymerase chain reaction (RT-PCR) showed that IL-1 mRNA staining increased significantly following IFNgamma stimulation. These results provide evidence for the first time that not only Schwann cells, but also peripheral nerve fibroblasts are a source of immunomodulatory cytokines within the PNS and may contribute to inflammatory processes in PNS disease.

Human thyroid fibroblasts exhibit a distinctive phenotype in culture: characteristic ganglioside profile and functional CD40 expression

Fibroblasts from different regions of the human body exhibit substantial phenotypic diversity, some of which relates to the capacity for cross-talk with cells of the immune system. We examine, for the first time, thyroid fibroblast biology in culture. Thyroid explants were placed in culture, and fibroblasts were outgrown and serially passaged. These fibroblasts take on a morphology in culture resembling cells from other anatomic regions. When treated with PGE2, they assume a stellate morphology similar to that of prostanoid-treated orbital fibroblasts. The ganglioside profile exhibited by these cells is distinct from that observed previously in orbital and dermal fibroblasts. They uniformly express Thy-1, a surface glycoprotein. Messenger RNA encoding CD40, a surface receptor found on bone marrow-derived cells, and CD40 protein were expressed constitutively at low levels. Interferon-gamma (500 U/ml) treatment for 48-72 h resulted in high levels of surface HLA-DR and CD40 display. When CD40 is engaged with CD40 ligand (CD40L), nuclear factor-kappaB binding activity is up-regulated as is interleukin (IL)-6 and IL-8 expression. IL-1beta treatment up-regulates the expression of IL-1alpha, IL-1beta, and PGE2. These observations suggest that thyroid fibroblasts possess the molecular machinery necessary for cross-talk with immunocompetent cells such as lymphocytes and mast cells through the CD40/CD40L complex, as well as through classic cytokine networks, and to participate potentially in the inflammatory response of the thyroid gland.