FDC-like Cells Research Articles

Akt, IL-4, and STAT Proteins Play Distinct Roles in Prostaglandin Production in Human Follicular Dendritic Cell-like Cells.

This study aimed to explore the role of Akt protein in the induction and inhibition of prostaglandin (PG) in human follicular dendritic cell (FDC)-like cells. FDC-like cells and B cells were isolated from human tonsils. PG production was assessed using enzyme immunoassay, while the upstream cyclooxygenase-2 (COX-2) protein levels were measured using immunoblotting with FDC-like cells transfected with Akt siRNA to analyze the impact of Akt knockdown. The COX-2 expression and PG production induced with IL-1β were significantly increased by Akt knockdown. However, IL-1β did not significantly alter either total or phosphorylated Akt protein levels. Akt knockdown resulted in the augmentation of COX-2 expression induced by B cells, although the addition of B cells did not significantly modulate both total and phosphorylated Akt proteins. In contrast, IL-4 specifically exhibited a potent inhibitory effect on COX-2 protein induction and PG production via STAT6. The inhibitory activity of IL-4 was not hampered by Akt knockdown. Interestingly, COX-2 expression levels induced with IL-1β were markedly modulated with STAT1 and STAT3 knockdown. STAT1 silencing resulted in further augmentation of COX-2, whereas STAT3 silencing prohibited IL-1β from stimulating COX-2 expression. The current results suggest that Akt, IL-4, and STAT1 play inhibitory roles in PG production in FDC-like cells and expand our knowledge of the immune inflammatory milieu.

Does HTLV-1 Infection Show Phenotypes Found in Sjögren's Syndrome?

Viruses are a possible cause for Sjögren’s syndrome (SS) as an environmental factor related to SS onset, which exhibits exocrine gland dysfunction and the emergence of autoantibodies. Although retroviruses may exhibit lymphocytic infiltration into exocrine glands, human T-cell leukemia virus type 1 (HTLV-1) has been postulated to be a causative agent for SS. Transgenic mice with HTLV-1 genes showed sialadenitis resembling SS, but their phenotypic symptoms differed based on the adopted region of HTLV-1 genes. The dominance of tax gene differed in labial salivary glands (LSGs) of SS patients with HTLV 1-associated myelopathy (HAM) and adult T-cell leukemia. Although HTLV-1 was transmitted to salivary gland epithelial cells (SGECs) by a biofilm-like structure, no viral synapse formation was observed. After infection to SGECs derived from SS patients, adhesion molecules and migration factors were time-dependently released from infected SGECs. The frequency of the appearance of autoantibodies including anti-Ro/SS-A, La/SS-B antibodies in SS patients complicated with HAM is unknown; the observation of less frequent ectopic germinal center formation in HTLV-1-seropositive SS patients was a breakthrough. In addition, HTLV-1 infected cells inhibited B-lymphocyte activating factor or C-X-C motif chemokine 13 through direct contact with established follicular dendritic cell-like cells. These findings show that HTLV-1 is directly involved in the pathogenesis of SS.

Inhibitory effect of HTLV-1 infection on the production of B-cell activating factors in established follicular dendritic cell-like cells.

IntroductionThe low frequency of ectopic germinal center in labial salivary glands of patients with human T‐cell leukemia virus type 1 (HTLV‐1) antibody‐positive Sjögren's syndrome (SS) suggests that HTLV‐1 has some effects on follicular dendritic cells (FDCs).MethodsWe used flow cytometry, immunofluorescence, and enzyme‐linked immunosorbent assays (ELISAs) to investigate the direct effect of HTLV‐1 on B‐cell activating factors produced by established FDC like cells obtained from excised human tonsils. We then measured the serum B‐cell activating factor (BAFF) and C‐X‐C motif ligand (CXCL) 13 concentrations of the HTLV‐1‐seropositive SS patients and the HTLV‐1‐seronegative SS patients by ELISA.ResultsAmong the 31 isolated specimens, 22 showed morphological characteristics of FDCs. Day 2‐cultured specimens showed expressions of CD14, CD23, CD40, intracellular adhesion molecule‐1 (ICAM‐1), and vascular cell adhesion molecule‐1. After 2 weeks, 12 of these specimens expressed ICAM‐1, FDC, and fibroblast cell marker. Intracellular BAFF and CXCL13 were constitutively expressed regardless of stimulation. After direct coculture with the HTLV‐1‐infected T‐cell line HCT‐5 or MT‐2, the BAFF and CXCL13 expressions on the FDC‐like cells were decreased in accord with the increased number of HCT‐5 and MT‐2 cells with styliform change and without HTLV‐1 Gag protein expression. Interferons upregulated the concentration of BAFF (but not CXCL13) in the culture supernatant, which showed a declining trend under the presence of HCT‐5 or MT‐2. The serum concentrations of BAFF and CXCL13 in the HTLV‐1‐seropositive SS patients were lower than those of the HTLV‐1 seronegative SS patients.ConclusionsHTLV‐1 partially inhibited the BAFF and CXCL13 expressions of established FDC‐like cells.

A paracrine effect of 15 (S)-hydroxyeicosatetraenoic acid revealed in prostaglandin production by human follicular dendritic cell-like cells

Lipid mediators play active roles in each stage of inflammation under physiological and pathologic conditions. We have investigated the cellular source and functions of several prostanoids in the immune inflammatory responses using follicular dendritic cell (FDC)-like cells. In this study, we report a novel finding on the role of 15(S)- hydroxyeicosatetraenoic acid (HETE). Our observation of 15(S)-HETE uptake by FDC-like cells prompted to hypothesize that 15(S)-HETE might have a regulatory role in the other branch of eicosanoid production. The effects of 15(S)-HETE on COX-2 expression and prostaglandin (PG) production were analyzed by immunoblotting and specific enzyme immunoassays. The addition of 15(S)-HETE resulted in elevated levels of COX-2 expression and PG production. The enhanced PG production was not due to growth stimulation of FDC-like cells since 15(S)-HETE did not modulate FDC-like cell proliferation by the culture period of PG measurement. Peroxisome proliferator-activated receptor gamma (PPARγ) seems to mediate the augmenting activity as the antagonist GW9662 dose- dependently prevented 15(S)-HETE from increasing PG production. In addition, PPARγ protein expression was readily detected in FDC-like cells. These effects of 15(S)-HETE were displayed in the combined addition with IL-1β. Based on these results, we suggest that 15(S)-HETE is an inflammatory costimulator of FDC acting in a paracrine fashion.

Prostaglandin E2 stimulates COX-2 expression via mitogen-activated protein kinase p38 but not ERK in human follicular dendritic cell-like cells

BackgroundProstaglandin E2 (PGE2) is an endogenous lipid mediator of inflammation. Its production is regulated by the rate-limiting upstream enzyme cyclooxygenase-2 (COX-2). We have recently demonstrated that the major cell type expressing COX-2 in the germinal center is follicular dendritic cell (FDC). In this study, to elucidate the molecular mechanism of PGE2 in COX-2 production, we asked whether mitogen-activated protein kinases ERK and p38 might regulate COX-2 expression.ResultsFDC-like cells were used to analyze the phosphorylation kinetics of ERK and p38 and the impact of genetic knockdown. PGE2 stimulation gave rise to a rapid increase of p38 but not ERK phosphorylation. In contrast, IL-1β induced phosphorylation of both MAPKs. Knockdown of p38 resulted in a marked suppression of COX-2 expression induced by either PGE2 or IL-1β. ERK knockdown did not significantly affect the effect of PGE2 and IL-1β on COX-2 induction. The differential results of p38 and ERK siRNA transfection were reproduced in the production of prostaglandins and in experiments performed with pharmacologic inhibitors.ConclusionsOur data indicate that p38 is essentially required for PGE2 to induce COX-2 expression in FDC-like cells. The current study helps to expand our understanding of the biological function of FDC at the molecular level and provides a potential rationale for the pharmacologic or genetic approaches to regulate p38 MAPK in the treatment of various inflammatory disorders.

15(S)-HETE plays a regulatory role in the immune inflammatory responses

Abstract Arachidonic acids are subjected to the enzymatic transformation by PGH2 synthase or lipoxygenase upon the liberation from the membrane phospholipid. Using in vitro and in vivo experimental models, we have investigated the cellular and molecular mechanisms in the production and function of arachidonic acid metabolites. Here we report that a downstream product of 15-lipoxygenase, 15-S-hydroxyeicosatetraenoic acid (15-S-HETE) is not produced by human follicular dendritic cell (FDC)-like cells but exerts a regulatory effect on prostaglandin production by this type of cells. 15-S-HETE appears to derive from endothelial cells. FDC-like cells, which were isolated from human tonsil, do not express 15-lipoxyenase or 5-lipoxygenase but metabolize 15-S-HETE into downstream products. Immunoblotting analysis and results with chemical inhibitors imply that 15-S-HETE acts on FDC-like cells via PPAR-γ and leukotriene B4 receptor 2. 15-S-HETE enhances or inhibits the expression of PGH2 synthase and resultant prostaglandin production in FDC-like cells, which depends on the types of co-stimulation. Based on these data, we suggest a novel cellular and molecular pathway of immune regulation mediated by arachidonic acid metabolites.

PGE2 stimulates COX-2 expression via EP2/4 receptors and acts in synergy with IL-1β in human follicular dendritic cell-like cells

PGE2 is the major lipid mediator of inflammation produced by multiple cell types including follicular dendritic cells (FDCs) of the lymphoid tissue. We have investigated the immunoregulatory function of PGE2 and its production mechanism using FDC-like cells isolated from human tonsil. Our recent observation of COX-2-inducing effect of PGE2 prompted us to identify the responsible receptor in this study. Pharmacologic approaches were adopted and Western blotting was utilized to measure protein expression levels. Agonists selective for EP2 and EP4 significantly stimulated COX-2 expression, while antagonists for these receptors prevented PGE2 from triggering COX-2 induction. The combined addition of EP2 and EP4 antagonists resulted in further inhibition of PGE2. In contrast, EP1 and EP3 antagonists failed to exhibit the inhibitory effect on PGE2-induced COX-2 expression. Since PGE2 achieves COX-2 induction by repressing Akt activation in FDC-like cells, we confirmed EP2 and EP4 being the targets of PGE2 by examining the effects of E-prostanoid (EP) agonists and antagonists on the level of Akt phosphorylation. After the identification of PGE2 receptor, we examined the effect of PGE2 on IL-1β-induced COX-2 expression. PGE2 and IL-1β brought about a synergistic induction of COX-2 expression. Taken together, this study implies the impact of the combined role of eicosanoids and cytokines in inflammatory milieu.

Activated human B cells stimulate COX-2 expression in follicular dendritic cell-like cells via TNF-α

In spite of the potential importance of cyclooxygenase (COX)-2 expression in the germinal center, its underlying cellular and molecular mechanisms are largely unknown. COX-2 is the key enzyme generating pleiotropic prostaglandins. Based on our previous findings, we hypothesized that lymphocytes would stimulate COX-2 expression in follicular dendritic cell (FDC) by liberating cytokines. In this study, we examined the effect of tonsillar lymphocytes on COX-2 expression in FDC-like cells by immunoblotting. B but not T cells induced COX-2 protein in a time- and dose-dependent manner. Sub-fractionation analysis of B cell subsets revealed that activated but not resting B cells were responsible for the COX-2 induction. Confocal microscopy of frozen tonsils demonstrated that FDCs indeed express COX-2 in situ, in line with the in vitro results. To identify the stimulating molecule, we added neutralizing antibodies to the coculture of FDC-like cells and B cells. COX-2 induction in FDC-like cells was markedly inhibited by TNF-α neutralizing antibody. Finally, the actual production of TNF-α by activated B cells was confirmed by an enzyme immunoassay. The current study implies an unrecognized cellular interaction between FDC and B cells leading to COX-2 expression during immune inflammatory responses.

Positive feedback effect of PGE2 on cyclooxygenase-2 expression is mediated by inhibition of Akt phosphorylation in human follicular dendritic cell-like cells

Prostaglandins (PGs) are bioactive lipid mediators generated from the phospholipids of cell membrane in response to various inflammatory signals. To understand the potential role of PGs in PG production itself during immune inflammatory responses, we examined the effect of PGE2, PGF2α, and beraprost on COX-2 expression using follicular dendritic cell (FDC)-like HK cells isolated from human tonsils. Those three PGs specifically augmented COX-2 protein expression in a dose-dependent manner after 4 or 8h of treatment. The enhancing effect was also reflected in the actual production of PGs and the viable cell recovery of germinal center B-cells. To investigate the underlying molecular mechanism, we examined the impact of PI3K inhibitors on PG-induced COX-2 expression. Interestingly, COX-2 induction by PGE2 and beraprost, but not PGF2α, was enhanced by wortmannin and LY294002. In line with this result, Akt phosphorylation was inhibited by PGE2 and beraprost but not by PGF2α. The distinct effect of PGE2 and beraprost from PGF2α was reproduced in Akt-knockdowned HK cells. Our current findings imply that PGE2 and PGI2 stimulate COX-2 expression in FDC by inhibiting Akt phosphorylation. Additional studies are warranted to determine the potential role of Akt as a therapeutic target in patients with inflammatory disorders.

Opposing roles of TGF-β in prostaglandin production by human follicular dendritic cell-like cells.

Prostaglandins (PGs) are recognized as important immune regulators. Using human follicular dendritic cell (FDC)-like HK cells, we have investigated the immunoregulatory role of PGs and their production mechanisms. The present study was aimed at determining the role of TGF-β in IL-1β-induced cyclooxygenase-2 (COX-2) expression by immunoblotting. COX-2 is the key enzyme responsible for PG production in HK cells. TGF-β, when added simultaneously with IL-1β, gave rise to an additive effect on COX-2 expression in a dose-dependent manner. However, TGF-β inhibited IL-1β-stimulated COX-2 expression when it was added at least 12h before IL-1β addition. The inhibitory effect of TGF-β was specific to IL-1β-induced COX-2 expression in HK cells. The stimulating and inhibitory effects of TGF-β were reproduced in IL-1β-stimulated PG production. Based on our previous results of the essential requirement of ERK and p38 MAPKs in TGF-β-induced COX-2 expression, we examined whether the differential activation of these MAPKs would underlie the opposing activities of TGF-β. The phosphorylation of ERK and p38 MAPKs was indeed enhanced or suppressed by the simultaneous treatment or pre-treatment, respectively. These results suggest that TGF-β exerts opposing effects on IL-1β-induced COX-2 expression in HK cells by differentially regulating activation of ERK and p38 MAPKs.

Context-Dependent Development of Lymphoid Stroma from Adult CD34(+) Adventitial Progenitors.

Despite the key role of primary and secondary lymphoid organ stroma in immunity, our understanding of the heterogeneity and ontogeny of these cells remains limited. Here, we identify a functionally distinct subset of BP3(-)PDPN(+)PDGFRβ(+)/α(+)CD34(+) stromal adventitial cells in both lymph nodes (LNs) and thymus that is located within the vascular niche surrounding PDPN(-)PDGFRβ(+)/α(-)Esam-1(+)ITGA7(+) pericytes. CD34(+) adventitial cells developed in late embryonic thymus and in postnatal LNs and in the thymus originated, along with pericytes, from a common anlage-seeding progenitor population. Using lymphoid organ re-aggregate grafts, we demonstrate that adult CD34(+) adventitial cells are capable of differentiating into multiple lymphoid stroma-like subsets including pericyte-, FRC-, MRC-, and FDC-like cells, the development of which was lymphoid environment-dependent. These findings extend the current understanding of lymphoid mesenchymal cell heterogeneity and highlight a role of the CD34(+) adventitia as a potential ubiquitous source of lymphoid stromal precursors in postnatal tissues.

Tonsil-derived mesenchymal stromal cells produce CXCR2-binding chemokines and acquire follicular dendritic cell-like phenotypes under TLR3 stimulation

We previously isolated mesenchymal stromal cells from human tonsils (T-MSCs) and showed the potential of these cells to differentiate into the mesodermal lineage and acquire a follicular dendritic cell (FDC) phenotype under cytokine stimulation. Because these T-MSCs were originally isolated from inflamed tonsillar tissues, we were curious about their activation status in response to innate immune stimuli, such as Toll-like receptors (TLRs). Therefore, we analyzed the expression profile of TLRs in T-MSCs and stimulated the T-MSCs with TLR agonists. TLR3 stimuli induced C–C chemokine receptor type 6 expression in T-MSCs after 24h. Furthermore, results from cytokine arrays showed increases in epithelial neutrophil-activating peptide-78/C-X-C motif chemokine (CXCL) 5, granulocyte chemotactic protein-2/CXCL6, growth-related oncogene-α/CXCL1, interleukin-8/CXCL8, and interferon gamma-induced protein-10/CXCL10. CD54 expression was also increased after TLR3 stimulation. However, co-culturing T-MSCs with human B cells did not induce B-cell proliferation. This suggests that TLR3 stimulates the differentiation of T-MSCs into FDC-like cells and induces chemokine secretion, possibly by recruiting C–X–C chemokine receptor 2-expressing immune cells. In addition, T-MSCs also appeared to exert immunomodulatory effects by inhibiting B-cell proliferation, possibly by down-regulating CD18.

Human follicular dendritic cells promote germinal center B cell survival by providing prostaglandins

Evidence for the immunoregulatory function of lipid molecules in addition to proteins is accumulating. Based on our previous reports on the production of prostaglandin E2 (PGE2) and prostacyclin by human follicular dendritic cells (FDCs), we hypothesized that these prostaglandins (PGs) have a regulatory effect on the survival, proliferation, and differentiation of germinal center B (GC) cells. We observed that PGE2 and a prostacyclin analog (beraprost) specifically enhanced the viable recovery of GC B cells in dose-dependent manners. FDC-like cells also mimicked the effect of PGE2, which was significantly inhibited in the presence of indomethacin. The viable recovery was due to the prevention of cell death by PGE2 and beraprost but did not result from augmented proliferation of GC B cells. The effect of PGE2 and beraprost was manifest when they were added at early times of the culture. Interestingly, we found that the combined addition of a pan-caspase inhibitor and a necroptosis inhibitor gave rise to a similar result to PGE2. Finally, PGE2 and beraprost enhanced the generation of both CD20−CD38+ plasma cells and CD20+CD38− memory B cells from GC B cells. Our current data suggest that FDCs play an important function of sustaining GC B cell survival by providing PGs. Our data also implies that selective cyclooxygenase inhibitors administered during infection or vaccination may have an adverse effect on the course of humoral immune response.

IL-4 and HDAC Inhibitors Suppress Cyclooxygenase-2 Expression in Human Follicular Dendritic Cells

Evidence for immunoregulatory roles of prostaglandins (PGs) is accumulating. Since our observation of PG production by human follicular dendritic cells (FDCs), we investigated the regulatory mechanism of PG production in FDC and attempted to understand the functions of released PGs in the responses of adjacent lymphocytes. Here, using FDC-like cells, HK cells, we analyzed protein expression alterations in cyclooxygenase-2 (COX-2) in the presence of IL-4 or histone deacetylase (HDAC) inhibitors. Both IL-4 and HDAC inhibitors suppressed COX-2 expression in dose-dependent manners. Their effect was specific to COX-2 and did not reach to COX-1 expression. Interestingly, HDAC inhibitors gave rise to an opposing effect on COX-2 expression in peripheral blood monocytes. Our results suggest that IL-4 may regulate COX-2 expression in FDCs by affecting chromatin remodeling and provide insight into the role of cellular interactions between T cells and FDC during the GC reaction. Given the growing interests in wide-spectrum HDAC inhibitors, the differential results on COX-2 expression in HK cells and monocytes raise cautions on their clinical use.

Syntenin Is Expressed in Human Follicular Dendritic Cells and Involved in the Activation of Focal Adhesion Kinase

Syntenin is an adaptor molecule containing 2 PDZ domains which mediate molecular interactions with diverse integral or cytoplasmic proteins. Most of the results on the biological function of syntenin were obtained from studies with malignant cells, necessitating exploration into the role of syntenin in normal cells. To understand its role in normal cells, we investigated expression and function of syntenin in human lymphoid tissue and cells in situ and in vitro. Syntenin expression was denser in the germinal center than in the extrafollicular area. Inside the germinal center, syntenin expression was obvious in follicular dendritic cells (FDCs). Flow cytometric analysis with isolated cells confirmed a weak expression of syntenin in T and B cells and a strong expression in FDCs. In FDC-like cells, HK cells, most syntenin proteins were found in the cytoplasm compared to weak expression in the nucleus. To study the function of syntenin in FDC, we examined its role in the focal adhesion of HK cells by depleting syntenin by siRNA technology. Knockdown of syntenin markedly impaired focal adhesion kinase phosphorylation in HK cells. These results suggest that syntenin may play an important role in normal physiology as well as in cancer pathology.

Tonsil-derived mesenchymal progenitor cells acquire a follicular dendritic cell phenotype under cytokine stimulation

Tonsils comprise part of the mucosal immune system and contain lymphocytes, macrophages, and follicular dendritic cells (FDCs). FDCs are located in the B cell area of the follicles of secondary lymphoid organs, such as the spleen, tonsils, or lymph nodes, and they trap and retain immune complexes on their surfaces to regulate B cell activation and maturation. Stromal cells from the palatine tonsils are often used for FDC in vitro studies, and it has been reported that human palatine tonsils may be a good source of multipotent mesenchymal cells. Therefore, we assessed whether tonsil-derived mesenchymal stromal cells could differentiate into a FDC-like phenotype. We discovered that stromal cells isolated from human tonsils not only had the potential to differentiate into various cell types of mesenchymal origin, but they also could differentiate into FDC-like cells under cytokine stimulation in vitro.

Tonsil-derived mesenchymal progenitor cells acquire a follicular dendritic cell phenotype under cytokine stimulation (120.34)

Abstract Tonsils comprise part of the mucosal immune system and contain lymphocytes, macrophages, and follicular dendritic cells (FDCs). FDCs are located in the B cell area of the follicles of secondary lymphoid organs, such as the spleen, tonsils, or lymph nodes, and they trap and retain immune complexes on their surfaces to regulate B cell activation and maturation. Stromal cells from the palatine tonsils are often used for FDC in vitro studies, and it has been reported that human palatine tonsils may be a good source of multipotent mesenchymal cells. Therefore, we assessed whether tonsil-derived mesenchymal stromal cells could differentiate into a FDC-like phenotype. We discovered that stromal cells isolated from human tonsils not only had the potential to differentiate into various cell types of mesenchymal origin, but they also could differentiate into FDC-like cells under cytokine stimulation in vitro.

Human follicular dendritic cells promote the APC capability of B cells by enhancing CD86 expression levels

Follicular dendritic cells (FDCs) are an essential cellular component of the germinal center (GC) and are believed to exert regulatory effects on the various stages of GC reactions. According to our previous reports, human FDCs express prostacyclin synthase, and prostacyclin analogues augment adhesion and co-stimulatory molecules on the surface of activated B cells. These findings prompted us to investigate whether FDCs would contribute to the antigen-presenting capability of B cells by using the well-established FDC-like cells, HK cells, and tonsillar B cells. Our results show that HK cells significantly enhance the expression levels of CD54, CD80, and CD86 on the surface of activated B cells. The enhancing effect of HK cells on CD86 is impeded by indomethacin and an EP4 antagonist, implying that a certain prostaglandin is mediating the up-regulation. Prostacyclin indeed recapitulates the enhancing effect on CD86, which is inhibited by EP4 as well as IP antagonists. B cells co-cultured with HK cells exhibit an augmented APC activity, which is inhibited by CD86 neutralization. These results reveal another unrecognized function of human FDC.

Identification and characterization of chondrogenic progenitor cells in the fascia of postnatal skeletal muscle

Intramuscular injection of bone morphogenetic proteins (BMPs) has been shown to induce ectopic bone formation. A chondrogenic phase is typically observed in this process, which suggests that there may exist a chondrogenic subpopulation of cells residing in skeletal muscle. Two prospective cell populations were isolated from rat skeletal muscle: fascia-derived cells (FDCs), extracted from gluteus maximus muscle fascia (epimysium) and muscle-derived cells (MDCs) isolated from the muscle body. Both populations were investigated for their cell surface marker profiles (flowcytometry analysis), proliferation rates as well as their myogenic and chondrogenic potentials. The majority of FDCs expressed mesenchymal stromal cell markers but not endothelial cell markers. FDCs underwent chondrogenic differentiation after BMP4 treatment in vitro, but not myogenic differentiation. Although MDCs showed chondrogenic potential, they expressed the myogenic cell marker desmin and readily underwent myogenic differentiation in vitro; however, the chondrogenic potential of the MDCs is confounded by the presence of FDC-like cells residing in the muscle perimysium and endomysium. To clarify the role of the muscle-derived myogenic cells in chondrogenesis, mixed pellets with varying ratios of FDCs and L6 myoblasts were formed and studied for chondrogenic potential. Our results indicated that the chondrogenic potential of the mixed pellets decreased with the increased ratio of myogenic cells to FDCs supporting the role of FDCs in chondrogenesis. Taken together, our results suggest that non-myogenic cells residing in the fascia of skeletal muscle have a strong chondrogenic potential and may represent a novel donor cell source for cartilage regeneration and repair.

Production of Prostaglandin E2and I2Is Coupled with Cyclooxygenase-2 in Human Follicular Dendritic Cells

BackgroundProstaglandins (PGs) play pathogenic and protective roles in inflammatory diseases. The novel concept of PGs as immune modulators is being documented by several investigators. By establishing an in vitro experimental model containing human follicular dendritic cell-like cells, HK cells, we reported that HK cells produce prostaglandin E2 (PGE2) and prostaglandin I2 (PGI2) and that these PGs regulate biological functions of T and B cells.MethodsTo investigate the respective contribution of cyclooxygenase-1 (COX-1) and COX-2 to PGE2 and PGI2 production in HK cells, we performed siRNA technology to knock down COX enzymes and examined the effect on PG production.ResultsBoth PGE2 and PGI2 productions were almost completely inhibited by the depletion of COX-2. In contrast, COX-1 knockdown did not significantly affect PG production induced by lipopolysaccharide (LPS).ConclusionThe current results suggest that mPGES-1 and PGIS are coupled with COX-2 but not with COX-1 in human follicular dendritic cell (FDC) and may help understand the potential effects of selective COX inhibitors on the humoral immunity.