Receptor tyrosine kinase-GPCR signal complexes.

The formation of complexes between growth factor receptors and members of a family of G-protein-coupled receptors whose natural ligands are S1P (sphingosine 1-phosphate) and LPA (lysophosphatidic acid) represents a new signalling entity. This receptor complex allows for integrated signalling in response to growth factor and/or S1P/LPA and provides a mechanism for more efficient activation (due to integrated close-proximity signalling from both receptor classes) of the p42/p44 MAPK (mitogen-activated protein kinase) pathway. This article provides information on the molecular events at the interface between receptor tyrosine kinases and S1P/LPA receptors. Examples include the PDGF (platelet-derived growth factor)-induced tyrosine phosphorylation of G(i)alpha, released upon S1P(1) receptor activation, which is required for initiation of the p42/p44 MAPK pathway. Critical to this event is the formation of endocytic vesicles containing functionally active PDGFbeta receptor-S1P(1) receptor complexes, which are internalized and relocated with components of the p42/p44 MAPK pathway. We also report examples of cross-talk signal integration between the Trk A (tropomyosin receptor kinase A) receptor and the LPA(1) receptor in terms of the NGF (nerve growth factor)-dependent regulation of the p42/p44 MAPK pathway. NGF induces recruitment of the LPA(1) receptor to the nucleus (delivery might be Trk A-dependent), whereupon the LPA(1) receptor may govern gene expression via novel nuclear signalling processes.

Acute-phase proteins in gingival crevicular fluid during experimentally induced gingivitis.

The dynamics of four acute-phase proteins were investigated in gingival crevicular fluid (GCF) during the course of a 21 day experimental gingivitis study. These acute-phase proteins were the protease inhibitors alpha 2-macroglobulin (alpha 2-M) and alpha 1-antitrypsin (alpha 1-AT) and the iron-binding proteins transferrin (TF) and lactoferrin (LF). 6 healthy volunteers ceased all oral hygiene procedures for 3 weeks. GCF was sampled at seven day intervals from two sites per subject by paper strips for 30 s during the experimental gingivitis period and for two additional weeks after the reinstitution of oral hygiene. The mainly serum derived alpha 2-M, alpha 1-AT and TF exhibited very similar dynamics which reflects their common origin in GCF. Their levels increased significantly from baseline and remained high for at least one week after the reinstitution of oral hygiene measures (repeated measures MANOVA; alpha 2-M: p = 0.015; alpha 1-AT: p = 0.012; TF: p = 0.02). This probably reflects increased vascular permeability in the gingivae and, to a lesser degree, local production by gingival inflammatory cells. In contrast to the serum derived acute-phase proteins, the neutrophil derived LF rose significantly from baseline (repeated measures MANOVA; p = 0.001) but dropped rapidly after the reinstitution of oral hygiene measures. This could be because dental plaque was removed and thus neutrophil chemotactic agents in the crevice were decreased.

Lactoferrin in the gingival crevice as a marker of polymorphonuclear leucocytes in periodontal diseases.

This study examined lactoferrin (LF) levels in gingival crevicular fluid (GCF) and set out to test the hypothesis that LF could act as a marker of crevicular polymorphonuclear leucocytes (PMN). Therefore, 2 experiments were conducted: (a) to quantify total LF (ng/30 s sample) in GCF; (b) to correlate LF levels (ng/microliters) and PMN numbers (PMNs/microliters) in gingival crevicular washings (GCW). GCF was collected from 71 sites in a total of 22 patients. These sites were classified on the basis of clinical indices of gingivitis (GI) and pocket depth (PD) into three clinical groups: 'healthy', 'gingivitis' and 'periodontitis'. GCWs were obtained from an additional 63 sites in 21 patients. LF in GCF and GCWs was assayed by a sandwich ELISA. Total leucocyte and differential counts were performed on the GCWs. GCF LF (ng/30 s) correlated positively with GI (r = 0.418, p < 0.001), PD (r = 0.415, p < 0.001) and GCF volume (r = 0.624, p < 0.001). Gingivitis (n = 21) and periodontitis sites (n = 24) demonstrated significantly higher (p < 0.05) total GCF LF than healthy (n = 26) sites. In GCWs LF (ng/microliters) showed stronger correlations with clinical indices (GI: r = 0.452, PD: r = 0.513, p < 0.001) than did PMN numbers (PMNs/microliters) (GI: r = 0.279, PD: r = 0.388, p < 0.05). LF correlated strongly with PMNs in GCWs (r = 0.531, p < 0.001) and provides a simple and effective marker of crevicular PMN numbers.

Endothelial cell leukocyte adhesion molecule-1 (ELAM-1) and intercellular adhesion molecule-1 (ICAM-1) expression in gingival tissue during health and experimentally-induced gingivitis.

The changes in vascular adhesion molecule expression and numbers of infiltrating leukocytes during a 21-day experimental gingivitis episode were investigated immunohistochemically. Monoclonal antibodies to ELAM-1 (1.2B6), ICAM-1 (6.5B5), CD3 (OKT3-pan-T cell) and neutrophils (PMN-elastase) were used to identify positive vessels and leukocytes within gingival biopsies taken on d 0, 7, 14 and 21. Vascular endothelium expressed ELAM-1 and ICAM-1 both in clinically 'healthy' tissue (d 0) and in experimentally inflamed tissue (d 7 to 21). Positive vessels were found mainly in the connective tissue subjacent to the junctional epithelium where the highest numbers of T cells and neutrophils were also seen. Although T cells were found in all tissue areas studied, neutrophils were largely concentrated in the junctional epithelium and the subjacent connective tissue but were absent from the oral epithelial region. As the experimental gingivitis developed, the number of T cells or neutrophils in the different tissue regions did not change significantly although the most intense vascular ICAM-1 and ELAM-1 staining redistributed to the CT adjacent to the junctional epithelium. A prominent feature was the intense ICAM-1 positive staining of the junctional epithelium and its absence in the closely adjacent oral epithelium, in both clinically 'healthy' and inflamed tissue. The gradient of ICAM-1 in junctional epithelium, with the strongest staining on the crevicular aspect plus the vascular expression of ELAM-1 and ICAM-1 in both clinically 'healthy' and inflamed tissue may be crucial processes which direct leukocyte migration towards the gingival crevice.

Langerhans cell dynamics in human gingiva during experimentally induced inflammation.

The changes in the number of Langerhans cells within the gingiva during a 21 day experimental gingivitis episode were investigated immunohistochemically. Monoclonal antibodies to CD1a (specific for Langerhans cells and thymocytes) and HLA-DR (class II major histocompatibility antigens - (MHC)) were used to identify Langerhans cells within gingival biopsies taken on days 0, 7, 14 and 21. HLA-DR antibody stained dendritic cells within the oral epithelium which were morphologically identical to the CD1a+ Langerhans cells. Class II MHC LC numbers rose and plateaued between day 7 and 14 then decreased to baseline by day 21. As plaque accumulated and initial inflammation developed there was an increase in the number of CD1a+ Langerhans cells which peaked at day 7 and stayed high (day 14). As inflammation developed there was a statistically significant decrease in the number of CD1a+ Langerhans cells by day 21 (p = 0.028). The initial increase, followed by a decrease in CD1a+ Langerhans cells as inflammation developed, suggests that migration of Langerhans cells occurs within the gingival epithelium and this may represent an important early event in the gingival immune response to plaque.

Bioassay of interleukin 1 (IL-1) in human gingival crevicular fluid during experimental gingivitis.

The cytokine IL-1 was demonstrated in crevicular fluid during a 14- and 21-day experimental gingivitis in healthy human volunteers. A sensitive and specific bioassay allowed detection of biologically active IL-1 at levels ranging from 0.18 ng/microliters at baseline to 1.70 ng/microliters in inflamed gingiva. Levels of IL-1 increased rapidly with plaque accumulation and in advance of the subsequent gingival inflammation, peaking within 7 days of the start of gingivitis. As changes in IL-1 were detected before clinically recognizable gingival changes, IL-1 may have potential as an early marker of gingival inflammatory changes.

Expression of transferrin receptors by monocytes and peritoneal macrophages from renal failure patients treated by continuous ambulatory peritoneal dialysis (CAPD).

Approximately 20% of monocytes and peritoneal macrophages from renal failure patients undergoing continuous ambulatory peritoneal dialysis (CAPD) were transferrin-receptor (TfR) positive by immunofluorescence, whereas cells from normal controls were generally TfR negative, as were monocytes from rheumatoid arthritis patients and from renal failure patients treated by haemodialysis. There was a significant correlation between the length of time on CAPD and the proportion of TfR-positive blood monocytes. CAPD peritoneal macrophages possessed 6.7-37.1 x 10(3) transferrin binding sites per cell, with a Ka of 3-25 x 10(7) mol l-1. In culture, monocytes from CAPD patients showed a progressive decrease in TfR expression, while in contrast about 20% of monocytes from normal controls which were originally 100% TfR negative expressed TfR after 3 days in culture. These findings indicate that regulation of TfR in monocytes/macrophages is complex, and that frequent removal of peritoneal cells during dialysate exchange may place a strain on the bone marrow, resulting in the release of an increasingly immature population of TfR positive monocytes to the circulation in CAPD patients.