Evidence for a role of VLA integrins in lymphocyte-human gingival fibroblast adherence

Induction of CD13 on T-lymphocytes by adhesive interaction with gingival fibroblasts

Lymphocytes in peripheral blood do not express CD13 (aminopeptidase N), a membrane alanyl metallopeptidase. However, it has been demonstrated that locally infiltrated lymphocytes in chronic inflammatory sites can be CD13-positive, and possible involvement of stromal cell adherence in the induction of CD13 has been suggested. In this study, we examined whether T-lymphocyte/gingival-fibroblast interaction can activate T-lymphocytes to express CD13. CD13 expression was induced on PMA-activated T-lymphocytes only when they adhered directly to human gingival fibroblasts (HGF) at 2 hrs after the co-culture began, while an increase in the enzyme activity of CD13 was also confirmed in activated T-lymphocytes that had been co-cultured with HGF. Furthermore, CD13-positive T-lymphocytes were detected in inflamed gingival tissues in vivo. Analysis of these results indicates that direct interaction with HGF is essential for the induction of CD13 expression on T-lymphocytes that was also observed in periodontitis lesions.

Adenosine regulates the IL-1 beta-induced cellular functions of human gingival fibroblasts

In this study we examined the influence of adenosine on the cellular functions of human gingival fibroblasts (HGF), such as the production of inflammatory cytokines and extracellular matrices (ECM), and the expression and function of adhesion molecules. Concerning the expression of adenosine receptors, RT-PCR analysis revealed that HGF expressed adenosine receptor A1, A2a and A2b, but not A3 mRNA. Ligation of adenosine receptors by adenosine or its related analogue, 2-chloroadenosine (2-CADO), N(6)-cyclopentyladenosine (CPA) or CGS21680 synergistically increased IL-1beta-induced IL-6 and IL-8 production. In terms of ECM expression, adenosine and the adenosine receptor agonists, 2-CADO and CPA, enhanced constitutive and IL-1beta-induced expression of hyaluronate synthase mRNA, but not the mRNA levels of other ECM, such as collagen type I, III and fibronectin. Moreover, the adherence of IL-1beta-stimulated HGF to activated lymphocytes was also inhibited by adenosine, which is in part explained by the fact that adenosine down-regulated the IL-1beta-induced expression of ICAM-1 on HGF. These results provide new evidence for the possible involvement of adenosine in the regulation of inflammatory responses in periodontal tissues.

Interleukin-1beta regulation of adhesion molecules on human gingival and periodontal ligament fibroblasts

BACKGROUND

Adhesion molecules have been implicated in the pathogenesis of rheumatoid arthritis and may also play a role in the pathogenesis of periodontal disease by promoting the recruitment and retention of leukocytes in gingival tissue.

METHODS

The aim of the present study was to evaluate the capacity of interleukin-1beta (IL-1beta) to regulate adhesion molecule expression on clinically healthy human gingival (HGF) and periodontal ligament (PDL) fibroblasts. The HGF (n = 6) and PDL (n = 3) fibroblasts were treated with 1.0 ng/ml of IL-1beta for 24 hours and then incubated with primary intercellular adhesion molecule-1 (ICAM-1) and vascular cellular adhesion molecule-1 (VCAM-1) antibodies followed by FITC-conjugated secondary antibodies. The expression of ICAM-1 and VCAM-1 was measured by immunofluorescence flow cytometry.

RESULTS

The levels of ICAM-1 expression in IL-1beta treated HGF and PDL fibroblasts were statistically significant (P < or = 0.05) compared to normal untreated controls using log-transformed data and 3-way analysis of variance. Both cells expressed VCAM-1 after IL-1beta treatment, but the levels were not statistically different from controls.

CONCLUSIONS

This study demonstrated that IL-1beta upregulated ICAM-1 expression in both HGF and PDL fibroblasts. Even though the level of VCAM-1 was not statistically different from both HGF and PDL fibroblasts treated with IL-1beta compared to controls, both cells do express the VCAM-1 molecules. These results suggest that ICAM-1 and VCAM-1 might be involved in the pathogenesis of periodontal disease.

Natural killer cells activate human dermal fibroblasts

Human dermal fibroblasts (HDF) undergo activation and secrete cytokines when cocultured with T cells. Here, we identify potent activators of HDF among human peripheral CD2(+)-lymphocytes. Populations with strong HDF activating capacity consisted essentially of cells with a natural killer (NK) surface marker phenotype (CD3(-), CD4(-), CD8(-), CD56(+)). Addition of these cells to HDF resulted in rapid increase of intracellular free calcium concentrations as an early rapid cell activation signal. Upregulation of mRNA encoding for the inflammatory cytokines IL-1 beta and IL-6 as well as for chemokines IL-8 and MCP-1 was detected after cells were cocultured. Elevated concentrations of IL-6 and IL-8 were found in coculture supernatants of HDF and NK-cells. Skin-homing NK cells leaving the blood-stream during an inflammatory skin reaction might therefore represent potent activators of local inflammatory cytokine and chemokine production.

Transcriptional activation of mRNA of intercellular adhesion molecule 1 and induction of its cell surface expression in normal human gingival fibroblasts by Mycoplasma salivarium and Mycoplasma fermentans

Lipoproteins in the cell membranes of both Mycoplasma salivarium and Mycoplasma fermentans were demonstrated to trigger the transcription of intercellular adhesion molecule-1 mRNA in normal fibroblasts isolated from human gingival tissue and to induce its cell surface expression by a mechanism distinct from that of Escherichia coli lipopolysaccharide. The lipid moiety of the lipoproteins was suggested to play a key role in the expression of the activity.

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.

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.

CD44-hyaluronate interaction participates in the adherence of T-lymphocytes to gingival fibroblasts

It has already been clarified that peripheral blood T-lymphocytes which had been activated with phorbol 12-myristate 13-acetate (PMA) acquired the ability to bind to human gingival fibroblasts (HGF) and that the adherence was mediated by VLA integrins. However, these studies also raised the possibility that molecules other than VLA integrins should be involved in the adherence between T-lymphocytes and HGF. In this study, the possible involvement of CD44, a hyaluronate receptor, in heterotypic cell-cell interactions was investigated. It was confirmed that PMA-activated T-lymphocytes strongly adhered to plate-coated hyaluronate and that the hyaluronate binding was clearly inhibited by the addition of OS/37, a newly established mAb specific for the hyaluronate-binding epitope on CD44. Interestingly, OS/37 also blocked the HGF binding of the activated T-lymphocytes when the adherence to HGF was assessed at 4 degrees C, at which temperature the adhesion of integrin molecules diminished, while that of CD44 functioned normally. Immunofluorescence staining revealed that hyaluronate was anchored along the cell surface of HGF. Furthermore, the binding of activated T-lymphocytes to HGF was significantly inhibited by the treatment of HGF with hyaluronidase. These results clearly demonstrated that CD44-hyaluronate interactions participated at least in part in the adhesiveness of T-lymphocytes to HGF.

Antigen-presenting-cell function of interferon gamma-treated human gingival fibroblasts

The present study was carried out to examine the antigen-presenting cell (APC) functions of human gingival fibroblasts (HGF) elicited with IFN gamma. Stimulation of HGF with IFN gamma clearly induced HLA-DR expression and enhanced expression of intercellular adhesion molecule-1 (ICAM-1) on HGF. Despite the phenotypical resemblance of IFN gamma-treated HGF to so-called APC, HLA-DR positive HGF were unable to induce proliferation of allo-reactive peripheral blood T cells (PBT) isolated from different donors. The failure of IFN gamma-treated HGF to stimulate unprimed allo-reactive PBT was not due to the lack of production of IL-1 or the immunosuppressive effect of PGE2 from HGF. On the other hand, the fact that detectable expression of CD80, ligand for CD28, was not found on IFN gamma-treated HGF may at least in part explain the ineffective function of HGF as APC. Interestingly, IFN gamma-treated HGF induced proliferation of primed allo-reactive CD4+ T cells in a HLA-DR dependent manner, suggesting that IFN gamma-treated HGF may have the ability to stimulate pre-activated T cells. We then confirmed that high levels of IFN gamma mRNA were detectable in inflamed gingival tissue. Although it cannot be concluded from this study that HGF are incapable of effectively presenting antigenic peptides to autologous T cells bearing appropriate T cell receptors, present results suggest that HGF may be affected by locally-secreted IFN gamma and that the IFN gamma-stimulated HGF may play a role in regulating immune responsiveness in inflammatory periodontal lesions.