Aspects of cell biology of the normal periodontium

Bone Regeneration Around Implants in the Canine Mandible With Cultured Fibroblasts in Polyglactin Mesh

BACKGROUND

Human fibroblast-derived dermal substitute (HFDDS) is a tissue-engineered material that consists of polyglactin mesh seeded with cultured fibroblasts. Cultured fibroblasts are not as differentiated as tissue fibroblasts and retain the ability to differentiate into other cells types. HFDDS also is capable of stimulating angiogenesis and wound healing. The purpose of this study was to attempt to evaluate the effects of HFDDS on guided bone regeneration at sites with 1.5-mm peri-implant defects in the canine mandible.

METHODS

Fifty sand-blasted acid-etched test implants were placed into the edentulous areas of mandibular ridges of five American foxhounds. Each site had a standardized 1.5-mm circumferential peri-implant defect in the coronal half of the implant, created by a specialized drill at the time of osteotomy. In each canine two implants received no treatment of the defects, four implants were treated with polyglactin mesh (carrier only) wrapped around the circumference of the defect wall, and four implants were treated with HFDDS placed in a similar fashion to the mesh. Implant sites healed submerged for 10 weeks, at which time sacrifice took place and sections were prepared, processed, and analyzed histomorphometrically.

RESULTS

The mean distance from the top of the fixture to the first point of bone-implant contact was 2.20 mm, 2.25 mm, and 2.60 mm for the HFDDS, carrier, and control sites, respectively (P = 0.202). Overall mean percentage of bone-to-implant contact (BIC) in the defects was 32.8%, 31.0%, and 22.8% for the HFDDS, carrier, and control groups, respectively. These differences were not statistically significant, but approached statistical significance for the control group compared to HFDDS and carrier (P = 0.057). Overall mean bone fill in the defects calculated histometrically was 36.0%, 35.8%, and 33.9% for the HFDDS, carrier, and control groups, respectively. These differences were not statistically significant. Sites with dehiscence at the time of implant placement had significantly greater distance to first bone-implant contact (P = 0.002), a smaller percentage of BIC (P = 0.006), and significantly less bone fill (P = 0.006) in the defects. It was consistently found that when dehiscence occurred on the buccal side of the implant, the outcomes for all parameters measured were significantly inferior on the lingual side as well. Factorial analysis, which grouped outcomes by dehiscence categories (none, partial, or full dehiscence), revealed that with intact defects without dehiscence, HFDDS had less bone fill compared to the carrier. However, in defects with partial or full dehiscence, HFDDS had more bone fill compared to carrier sites. These differences were statistically significant (P = 0.034).

CONCLUSIONS

In intact sites without dehiscence, the presence of cultured fibroblasts in 1.5-mm-wide peri-implant defects did not significantly enhance bone regeneration compared to the carrier, polyglactin mesh. However, sites with partial or full dehiscence treated with HFDDS had significantly greater bone fill compared to the carrier (P = 0.034). When dehiscence occurs during immediate implant placement on narrow ridges without the use of membranes, bone regeneration tends to be inferior on the side of the dehiscence as well as the opposite side of the implant.

Lipopolysaccharide-binding protein down-regulates the expression of interleukin-6 by human gingival fibroblast

BACKGROUND

Lipopolysaccharide-binding protein (LBP) participates in the interaction of lipopolysacchaide (LPS) with CD14 to modulate the expression of cytokines. Human gingival fibroblast may actively participate in LPS-induced immuno-inflammatory responses through CD14, toll-like receptor (TLR) superfamily, MD-2 and related adaptive proteins, leading to the expression of cytokines.

OBJECTIVES

The present in vitro study aimed to investigate the possible effect of LBP and E. coli LPS interaction on the expression of cellular LPS receptors and IL-6 by human gingival fibroblast.

METHODS

The mRNA expression of CD14, LBP, TLR-2, TLR-4, MD-2 and IL-6 in human gingival fibroblast explants was detected by reverse transcriptionpolymerase chain reaction (RT-PCR) in the presence or absence of E. coli LPS and recombinant human LBP (rhLBP), while IL-6 peptides were analyzed by ELISA and immunohistochemistry, respectively.

RESULTS

Human gingival fibroblast could constitutively express CD14, MD-2 and IL-6 mRNAs, but not TLR-2, TLR-4 and LBP mRNAs. E. coli LPS induced the messages expression of MD-2, TLR-2 and -4. The expression of both IL-6 message and peptide was up-regulated by E. coli LPS in a dose dependent manner. Whereas rhLBP could significantly down-regulate the expression of both mRNAs and peptides of CD14 and IL-6 but not MD-2 signals in the presence or absence of E. coli LPS. The up-regulated expression of TLR-2 and -4 by E. coli LPS no longer existed in the presence of rhLBP.

CONCLUSIONS

This study suggests that LBP may down-regulate the expression of IL-6 by human gingival fibroblast. Further studies are warranted to clarify the molecular mechanisms of LBP in regulation of cytokine expression by host cells and to elaborate the relevant clinical implications.

Expression of growth factors in the gingival crevice fluid of patients with phenytoin-induced gingival enlargement

The mechanism underlying phenytoin (PHT)-induced gingival enlargement (GE) is not yet known. The aim of the present study was to investigate transforming growth factor-beta1 (TGF-beta1), platelet-derived growth factor-BB (PDGF-BB) and basic fibroblast growth factor (bFGF) profiles in the gingival crevice fluid (GCF) of patients with PHT-induced GE and to compare the results with healthy controls. Five PHT-treated patients and five healthy subjects with normal periodontal tissue were included in this study. GCF samples were collected from (i) enlarged gingival sites in patients receiving PHT (GE+); (ii) non-enlarged gingival sites in the same patients (GE-); (iii) normal gingival sites of healthy subjects (control). The levels of TGF-beta1, PDGF-BB and bFGF in the GCF samples were analysed by ELISA. The results showed that the total amounts of TGF-beta1 and PDGF-BB in the GE+ group were higher than in the GE- group and significantly higher than in the control group (P < 0.05). However, no significant differences were found between the groups when the concentrations of these growth factors were compared. bFGF levels were not compared as this growth factor could be detected in only 33, 41 and 44% of the GE+, GE- and control GCF samples, respectively. These results show that TGF-beta1 and PDGF-BB are readily detectable in GCF obtained from enlarged and non-enlarged sites of PHT recipients and suggest that since the amounts were markedly higher at the GE+ than the GE- sites, the systemic administration of PHT has a pronounced localised effect on the levels of these growth factors. Moreover, our findings provide evidence that both TGF-beta1 and PDGF-BB are closely associated with the clinical manifestation of PHT-induced GE.

Porphyromonas gingivalis lipopolysaccharide signaling in gingival fibroblasts-CD14 and Toll-like receptors

Periodontal disease is the major cause of adult tooth loss and is commonly characterized by a chronic inflammation caused by infection of oral bacteria. Porphyromonas gingivalis (P. gingivalis) is one of the suspected periodontopathic bacteria and is frequently isolated from the periodontal pockets of patients with chronic periodontal disease. The lipopolysaccharide (LPS) of P. gingivalis is a key factor in the development of periodontitis. Gingival fibroblasts, which are the major constituents of gingival connective tissue, may directly interact with bacteria and bacterial products, including LPS, in periodontitis lesions. It is suggested that gingival fibroblasts play an important role in the host responses to LPS in periodontal disease. P. gingivalis LPS enhances the production of inflammatory cytokines such as interleukin (IL)-1, IL-6, IL-8, and tumor necrosis factor alpha (TNF-alpha) in gingival fibroblasts. However, the receptor that binds with P. gingivalis LPS on gingival fibroblasts remained unknown for many years. Recently, it was demonstrated that P. gingivalis LPS binds to gingival fibroblasts. It was also found that gingival fibroblasts express CD14, Toll-like receptor 4 (TLR4), and myeloid differentiation primary response gene 88 (MyD88). P. gingivalis LPS treatment of gingival fibroblasts activates several intracellular proteins, including protein tyrosine kinases, and up-regulates the expression of monocyte chemoattractant protein-1 (MCP-1), extracellular signal-regulated kinase 1 (ERK1), and signal-regulated kinase 2 (ERK2), IL-1 receptor-associated kinase (IRAK), nuclear factor-kappaB (NF-kappaB), and activating protein-1 (AP-1). These results suggest that the binding of P. gingivalis LPS to CD14 and TLR4 on gingival fibroblasts activates various second-messenger systems. In this article, we review recent findings on the signaling pathways induced by the binding of P. gingivalis LPS to CD14 and Toll-like receptors (TLRs) in gingival fibroblasts.

Quantitative evaluation of the vasculature and fibronectin localization in gingival connective tissue of smokers and non-smokers

BACKGROUND

It has been shown that tobacco is a significant risk factor for periodontal disease. The reason for decreased gingival bleeding in smokers is not known. The aim of the present study was to demonstrate the localization of fibronectin in the extracellular matrix of the inflamed gingiva of smokers and non-smokers and to evaluate the chronic effect of smoking on the gingival microvessel number (NVES) and vascular surface density (VSD).

METHODS

Seventy-four (74) adult patients with periodontitis were included in this investigation. Of these patients, 38 were smokers and 36 were non-smokers. Probing depths (PD), papillary bleeding index (PBI) of both groups, and the smoking habits of the smokers were recorded. Biopsy specimens obtained during periodontal surgery were prepared to evaluate fibronectin distribution and to quantitate the vasculature.

RESULTS

The mean VSD values of smokers and non-smokers were 6.721 +/- 1.845 and 5.721 +/- 3.118 (mean +/- SD), and the mean NVES of smokers and non-smokers was 31.582 +/- 11.810 and 30.145 +/- 15.442, respectively. The difference between the mean PD and PBI values of the 2 groups was not statistically significant. The location of the biopsy specimen, whether in the anterior or posterior area of the mouth, did not lead to any statistically significant differences between the groups. In addition, the number of years smoked and the tobacco brand used did not result in statistically significant differences. The most intense staining of fibronectin was observed beneath the epithelium around the blood vessels of the uppermost region of the connective tissue, showing a fibrillar and diffuse distribution; however, there was no significant difference between smokers and non-smokers.

CONCLUSION

The results of the present study indicate that smoking does not affect the vascular surface density, number of vessels per mm2 stroma, or fibronectin distribution in subepithelial gingival connective tissue.

Evaluation of p53, bcl-2, and interleukin-15 levels in gingival crevicular fluid of cyclosporin A-treated patients

BACKGROUND

Apoptosis plays an important role in the maintenance of tissue homeostasis. Considering that apoptosis mediators may play a role in the pathogenesis of drug-induced gingival overgrowth, this study was conducted to evaluate p53, bcl-2, and interleukin-15 (IL-15) levels in gingival crevicular fluid (GCF) of cyclosporin A (CsA)-treated patients.

METHODS

Twenty renal transplant patients exhibiting CsA-induced gingival overgrowth and 15 systemically healthy gingivitis patients were included in the study; 15 systemically and periodontally healthy volunteer subjects served as the healthy control group. GCF samples were obtained from one interdental site with gingival overgrowth (GO+) and one site without (GO-) from each CsA-treated patient; hyperplasia index, probing depth, papilla bleeding index, and plaque presence were recorded. One site from each gingivitis patient and healthy control was selected, GCF samples were obtained, and the same clinical parameters were recorded. GCF p53, bcl-2, and IL-15 levels were analyzed by enzyme-linked immunosorbent assay. The results were tested statistically.

RESULTS

p53 and bcl-2 levels were below the minimum detectable level in all GCF samples analyzed. CsA GO+ and CsA GO- sites, as well as gingivitis sites, exhibited significantly higher GCF levels of IL-15 compared to healthy controls (P<0.05). The difference between CsA GO+ sites and gingivitis sites was not statistically significant, although the total amount of IL-15 in CsA GO+ sites was lower than gingivitis sites (P>0.05). The total amount of IL-15 in CsA GO- sites was significantly lower than gingivitis sites (P<0.05). No significant correlation was found between the clinical parameters and GCF IL-15 levels (P>0.05).

CONCLUSIONS

The pathogenesis of CsA-induced gingival overgrowth is multifactorial. The findings of the present study indicate that IL-15 may play a role in the pathogenesis of CsA-induced gingival overgrowth due to its interactions with CsA and its role in apoptosis and inflammation.

Salivary carcinoembryonic antigen as an inflammatory marker

In this study we examined concentration of carcinoembryonic antigen (CEA) in paired saliva and serum samples from healthy individuals and patients with periodontal disease. CEA concentration was determined immunoradiometrically using highly specific anti-CEA antibodies. The salivas from periodontally healthy subjects revealed CEA concentrations with median value of 62 mg/L. Distribution of salivary CEA concentrations in patients with periodontal diseases were very broad with median values: 74 mg/L (stage I), 84 mg/L (stage II), 240 mg/L (stage III) and 412 mg/L (necrotizing ulcerative periodontitis-NUP). Analysis of the obtained values indicated statistically significant increase in salivary CEA, in subjects with periodontal diseases. Metronisadole treatment in patients with NUP leads to statistically significant decrease in salivary CEA. The results obtained suggested salivary CEA as a potential marker of the alterations of periodontium.

Cytokine regulation of syndecan-1 and -2 gene expression in human periodontal fibroblasts and osteoblasts

Cell-surface proteoglycans participate in several biological functions including interactions with a variety of growth factors and cytokines. Regulation of syndecan-1 and -2 gene expression was investigated in human periodontal ligament fibroblasts (PDLF), osteoblasts (OB) and gingival fibroblasts (GF), in response to platelet-derived growth factor (PDGF-BB), transforming growth factor (TGF-beta 1), and interleukin (IL-1 beta) by Northern blot analyses. We also compared the effect of PDGF-BB and TGF-beta 1, separately and in combination, in the prolonged presence of IL-1 beta on the expression of both syndecan genes. The results demonstrated that the three cell lines regulated the expression of syndecan-1 and -2 in response to growth factors and cytokines in different manners. These cell lines increased syndecan-1 mRNA levels in response to either PDGF-BB or TGF-beta 1 and decreased levels in response to IL-1 beta. The effect of IL-1 beta on syndecan-1 mRNA synthesis was partially reversed after adding PDGF-BB and TGF-beta 1, separately or in combination, in the presence of IL-1 beta. In contrast, syndecan-2 mRNA level was markedly upregulated in response to either TGF-beta 1 or IL-1 beta in OB when compared with the other two cell lines. However, the stimulatory effect of TGF-beta 1 on syndecan-2 mRNA production in OB was abolished in the prolonged presence of IL-1 beta. These findings lend support to the notion that syndecan-1 and syndecan-2 have distinct functions which correlate with their source and functions within the periodontium.

Evaluation of transforming growth factor-beta 1 level in crevicular fluid of cyclosporin A-treated patients

BACKGROUND

The aim of the present study was to investigate the level of transforming growth factor-beta 1 (TGF-beta 1) in gingival crevicular fluid (GCF) samples of cyclosporin A (CsA)-treated patients and to compare the results with control groups.

METHODS

Fourteen renal transplant patients exhibiting severe CsA-induced gingival overgrowth, 10 patients with chronic gingivitis, and 10 subjects with clinically healthy periodontium were included in the study. In CsA-treated patients, GCF samples were harvested from sites exhibiting gingival overgrowth (CsA GO+) and sites not exhibiting gingival overgrowth (CsA GO-). The TGF-beta 1 levels in a total of 96 GCF samples from the 34 participants were analyzed by enzyme-linked immunosorbent assay. The results were expressed in terms of total amount (pg/2 sites) and concentration (ng/ml).

RESULTS

TGF-beta 1 total amounts in CsA GO+ and CsA GO- sites were similar and significantly higher than that of healthy sites (P < 0.02 and P < 0.01, respectively). The total amount of TGF-beta 1 was also higher in gingivitis sites compared to the healthy sites, but the difference was not statistically significant (P > 0.05). CsA GO+ and CsA GO- sites exhibited higher total amount and concentration of TGF-beta 1 than that of gingivitis sites, but the differences were insignificant (P > 0.05).

CONCLUSIONS

The results of the present study support the theory that CsA increases the synthesis of TGF-beta 1 in GCF. However, since the difference between CsA GO+ and CsA GO- sites was not statistically significant, it seems unlikely that GCF TGF-beta 1 level is the sole factor responsible for the CsA-induced gingival overgrowth. Complex interactions between various mediators of inflammation and tissue modeling are possibly involved in the pathogenic mechanisms of this side effect.

Growth factors and cytokines modulate gene expression of cell-surface proteoglycans in human periodontal ligament cells

Cell-surface proteoglycans have been known to be involved in many functions including interactions with components of the extracellular microenvironment, and act as co-receptors which bind and modify the action of various growth factors and cytokines. The purpose of this study was to determine the regulation by growth factors and cytokines on cell-surface proteoglycan gene expression in cultured human periodontal ligament (PDL) cells. Subconfluent, quiescent PDL cells were treated with various concentrations of serum, bFGF, PDGF-BB, TGF-beta1, IL-beta1, and IFN-gamma. RT-PCR technique was used, complemented with Northern blot for syndecan-1, to examine the effects of these agents on the mRNA expression of five cell-surface proteoglycans (syndecan-1, syndecan-2, syndecan-4, glypican and betaglycan). Syndecan-1 mRNA levels increased in response to serum, bFGF and PDGF-BB, but decreased in response to TGF-beta1, IL-1beta and IFN-gamma. In contrast, syndecan-2 mRNA levels were upregulated by TGF-beta1 and IL-1beta stimulation, but remained unchanged with the other agents. Betaglycan gene expression decreased in response to serum, but was upregulated by TGF-beta1 and unchanged by the other stimulants. Additionally, syndecan-4 and glypican were not significantly altered in response to the regulator molecules studied, with the exception that glypican is decreased in response to IFN-gamma. These data demonstrate that the gene expression of the five cell-surface proteoglycans studied is differentially regulated in PDL cells lending support to the notion of distinct functions for these cell-surface proteoglycans.

Direct interaction between gingival fibroblasts and lymphoid cells induces inflammatory cytokine mRNA expression in gingival fibroblasts

In inflamed periodontal lesions, dense infiltration of lymphocytes is usually observed in the extravascular periodontal connective tissue, adjacent to gingival fibroblasts. Our previous study revealed that activated lymphocytes can adhesively interact with gingival fibroblasts in vitro. In the present study, we investigated whether gingival fibroblasts are activated through direct interaction with lymphoid cells by monitoring the expression of inflammatory cytokine mRNA in human gingival fibroblasts (HGF). Co-culture with various human lymphoid cells in vitro resulted in a marked increase in the expression of IL-1alpha, IL-1beta, and IL-6 mRNA by the HGF. In addition, expression of the mRNA of the IL-1beta-converting enzyme (ICE), which is essential to produce the mature form of IL-1beta, was constitutively observed in the HGF, suggesting that mature IL-1beta is produced by these cells. When HGF were cultured with the culture supernatant of the lymphoid cells, the increase in the inflammatory cytokine mRNA expression was not observed. Similarly, when HGF and lymphoid cells were cultured in the same well but separated by a membrane which prevented direct contact between the cells, no increase in inflammatory cytokine mRNA expression was observed. These results strongly indicate that direct interaction between these heterotypic cell types transduces activation signals into HGF that induce an increase in inflammatory cytokine mRNA expression. Furthermore, IL-1beta mRNA expression in the HGF was synergistically increased when HGF directly interacted with lymphoid cells in the presence of exogeneous IL-1beta. The present study demonstrates that direct interaction between HGF and lymphoid cells stimulates HGF to increase inflammatory cytokine mRNA expression, and raises the possibility that heterotypic cell-cell interaction may facilitate local inflammatory reactions.

Cytokine expression in periodontal health and disease

Soluble proteins that serve as mediators of cell function and are produced by various cell types, such as structural and inflammatory cells, are collectively called cytokines. Several lines of evidence have revealed that cytokines play important roles not only in tissue homeostasis but also in the pathogenesis of many infectious diseases. Recent research on biological activities in normal periodontium and the pathogenesis of periodontal diseases has clarified the involvement of various cytokines in the biological activities observed in the sites. Cytokines play crucial roles in the maintenance of tissue homeostasis, a process which requires a delicate balance between anabolic and catabolic activities. In particular, growth factors--such as fibroblast growth factor (FGF), platelet-derived growth factor (PDGF), insulin-like growth factor (IGF), transforming growth factor-beta (TGF-beta)--are thought to play important roles in modulating the proliferation and/or migration of structural cells in the periodontium and the production of various extracellular matrices by these cells. On the other hand, there is little doubt that excessive and/or continuous production of cytokines in inflamed periodontal tissues is responsible for the progress of periodontitis and periodontal tissue destruction. Particularly, inflammatory cytokines--such as IL-1 alpha, IL-1 beta, IL-6, and IL-8--are present in the diseased periodontal tissues, and their unrestricted production seems to play a role in chronic leukocyte recruitment and tissue destruction. It is possible that monitoring cytokine production or its profile may allow us to diagnose an individual's periodontal disease status and/or susceptibility to the disease. In addition, although the hypothesis is still controversial, it has been suggested that discrete T-cell subsets (Th1 and Th2) with different cytokine profiles play specific roles in the immunopathogenesis of periodontal diseases.

Expression of receptors for basic fibroblast growth factor on human periodontal ligament cells

Basic fibroblast growth factor (FGF-2; bFGF) is a major mitogen for connective tissue cells, and participates in the healing process. It has already been reported that FGF-2 could be applicable to enhance periodontal regeneration. In the present study, we examined FGF receptor (FGFR) expression on human periodontal ligament (PDL) cells. The binding of [125I]-labeled FGF-2 to human PDL cells was studied by radioreceptor assay. The binding of [125I]-FGF-2 to PDL cells reached a plateau after 2.5 h incubation at 4 degrees C and was inhibited by the addition of unlabeled FGF-2 and acidic FGF (FGF-1; aFGF), but not insulin-like growth factor-I, platelet-derived growth factor and transforming growth factor-beta 1. Scatchard analysis revealed the presence of approximately 1.0 x 10(5) FGF-2 binding sites per cell with an apparent Kd of 1.2 x 10(-10) M. Interestingly, the binding of [125I]-FGF-2 on PDL cells reached its maximum at d 6 of the culture and then gradually decreased. Scatchard analysis also demonstrated that the number of FGFRs on a PDL cell was altered during the course of the culture, while the affinity between FGF-2 and its receptor was not. The responsiveness of PDL cells to FGF-2, which was monitored by the inhibitory effect on alkaline phosphatase activity, was reduced in proportion to the decrease in the number of FGFRs on the PDL cells. The present study suggests that PDL cells alter the responsiveness to FGF-2 during the course of the culture by changing the density of its receptor, and that the density of FGFR expression might be a marker of the cytodifferentiation of PDL cells into mineralized tissue forming cells.

Cyclosporin A and hydroxycyclosporine (M-17) affect the secretory phenotype of human gingival fibroblasts

The responsiveness of human gingival fibroblast populations to cyclosporin A (CsA) and its principal metabolite, hydroxycyclosporine (M17), was evaluated in cell culture. Gingival fibroblasts exhibited a dose-dependent accumulation and bell-shaped distribution of dansylated CsA. A 100-fold excess of non-labeled CsA prevented the accumulation of the fluorescent probe in the fibroblasts. Both CsA (400 ng/ml) and M17 (100 ng/ml) stimulated mean gingival fibroblast cell number to 23.2% and 36.7% above controls, and reduced mean collagen production by 37.7% and 37.4% below controls, respectively; however, neither CsA nor M17 affected mean protein production in comparison to control cultures. Analyses of responses to CsA and M17 by ligand-accumulating and non-accumulating fibroblasts sorted out from the parent cultures did not provide consistent interstrain responses either by cells representing the upper quartile of fluorescence or cells representing the bottom quartiles of fluorescence. These data demonstrate that CsA is accumulated by gingival fibroblasts and that CsA and M17 are potent modulators of gingival fibroblast phenotype.

Effects of basic fibroblast growth factor on human periodontal ligament cells

In order to clarify the regulatory mechanisms of periodontal regeneration by basic fibroblast growth factor (bFGF), effects of bFGF on proliferation, alkaline phosphatase activity, calcified nodule formation and extracellular matrix synthesis of human periodontal ligament (PDL) cells were examined in this study. bFGF enhanced the proliferative responses of PDL cells in a dose-dependent manner. The maximum mitogenic effect of bFGF on PDL cells was observed at the concentration of 10 ng/ml. In contrast, bFGF inhibited the induction of alkaline phosphatase activity and the mineralized nodule formation by PDL cells. Moreover, employing the reverse transcription-polymerase chain reaction (RT-PCR) technique, we observed that the levels of laminin mRNA of human PDL cells was specifically upregulated by bFGF stimulation, but that of type I collagen mRNA was downregulated. On the other hand, the expression of type III collagen and fibronectin mRNA were not altered even when the cells were activated by bFGF. These results suggest that suppressing cytodifferentiation of PDL cells into mineralized tissue forming cells, bFGF may play a role in wound healing by inducing growth of immature PDL cells and that in turn accelerates periodontal regeneration.

Lymphocyte-fibroblast interactions

Chronic inflammatory reactions are usually characterized by inflammatory cell accumulation in the extravascular connective tissue. In such sites, inappropriate activation of circulating or resident lymphocytes becomes self-perpetuating and can lead to chronic tissue destruction. In addition to that, the locally infiltrated lymphocytes should have an opportunity to interact directly with fibroblasts composing the connective tissue. The direct interactions of those different cell types seem to play important roles in lymphocyte lodging and retention in such sites. Thus, for clarification of the immunopathogenesis of the chronic inflammatory diseases, including periodontitis, it is important that the molecular mechanisms involved in the heterotypic cell-cell interactions be revealed. In fact, it has been demonstrated that lymphocytes interact with various non-hematopoietic cells, such as epithelial cells and endothelial cells. Regarding interactions with fibroblasts, it has been shown that IFN gamma-stimulated fibroblasts can regulate the proliferative responses of T-lymphocytes both positively and negatively. Furthermore, activated lymphocytes have demonstrated strong binding ability to various fibroblast cell lines. Blocking experiments utilizing monoclonal antibodies specific to various cell adhesion molecules revealed that very late antigen (VLA) integrins, lymphocyte-function-associated antigen (LFA-1)/intercellular adhesion molecule-1 (ICAM-I), CD44/hyarulonate are, at least in part, involved in lymphocyte-fibroblast interactions. In addition, recent findings raised the possibility that the adhesive interactions between lymphocytes and fibroblasts influenced the various cellular functions of each cell type. In fact, it was recently demonstrated that the adhesive interactions stimulated fibroblasts to increase expression of inflammatory cytokine mRNA. These results strongly suggest that fibroblasts are not merely innocent bystanders but actively participate in local inflammatory reactions by directly interacting with locally infiltrated lymphocytes.