Philip B. Sugerman

The pathogenesis of oral lichen planus

Both antigen-specific and non-specific mechanisms may be involved in the pathogenesis of oral lichen planus (OLP). Antigen-specific mechanisms in OLP include antigen presentation by basal keratinocytes and antigen-specific keratinocyte killing by CD8(+) cytotoxic T-cells. Non-specific mechanisms include mast cell degranulation and matrix metalloproteinase (MMP) activation in OLP lesions. These mechanisms may combine to cause T-cell accumulation in the superficial lamina propria, basement membrane disruption, intra-epithelial T-cell migration, and keratinocyte apoptosis in OLP. OLP chronicity may be due, in part, to deficient antigen-specific TGF-beta1-mediated immunosuppression. The normal oral mucosa may be an immune privileged site (similar to the eye, testis, and placenta), and breakdown of immune privilege could result in OLP and possibly other autoimmune oral mucosal diseases. Recent findings in mucocutaneous graft-versus-host disease, a clinical and histological correlate of lichen planus, suggest the involvement of TNF-alpha, CD40, Fas, MMPs, and mast cell degranulation in disease pathogenesis. Potential roles for oral Langerhans cells and the regional lymphatics in OLP lesion formation and chronicity are discussed. Carcinogenesis in OLP may be regulated by the integrated signal from various tumor inhibitors (TGF-beta 1, TNF-alpha, IFN-gamma, IL-12) and promoters (MIF, MMP-9). We present our recent data implicating antigen-specific and non-specific mechanisms in the pathogenesis of OLP and propose a unifying hypothesis suggesting that both may be involved in lesion development. The initial event in OLP lesion formation and the factors that determine OLP susceptibility are unknown.

Autocytotoxic T-cell clones in lichen planus

We examined the in vitro cytotoxic activity of cutaneous T‐cell lines and clones from lichen planus (LP) patients against autologous epidermal keratinocytes. T cells were cultured from LP lesions and adjacent clinically normal skin and cloned by limiting dilution. Keratinocytes were cultured from LP lesions and adjacent clinically normal skin and immortalized by transfection with the E6 and E7 genes from human papillomavirus 16 (HPV16). The lesional T‐cell line from one LP patient contained 27% γδ+ T cells and was significantly more cytotoxic against autologous lesional keratinocytes than the T‐cell line from clinically normal skin. Clones isolated from the lesional T‐cell line were significantly more cytotoxic against autologous lesional keratinocytes than clones isolated from the non‐lesional T‐cell line. Most cytotoxic clones from LP lesions were CD8+ and most non‐cytotoxic clones from LP lesions were CD4+. One cytotoxic clone was CD4– and CD8– and expressed the γδ T‐cell receptor. Two CD8+ LP lesional T‐cell clones showed dose‐dependent killing of HPV16 E6/E7‐immortalized autologous lesional and normal keratinocytes, but no cytotoxic activity against Epstein–Barr virus‐transformed autologous B‐cell blasts. The cytotoxic activity of CD8+ lesional T‐cell clones against autologous lesional keratinocytes was partially blocked with anti‐major histocompatibility complex (MHC) class I monoclonal antibodies. These data support the hypothesis that CD8+ lesional T cells recognize an antigen associated with MHC class I on lesional keratinocytes and that CD8+ cytotoxic T cells lyse keratinocytes in LP lesions.

Matrix metalloproteinases and their inhibitors in oral lichen planus

Background: Oral lichen planus (OLP) is characterized by a sub‐epithelial lymphocytic infiltrate, basement membrane (BM) disruption, intra‐epithelial T‐cell migration and apoptosis of basal keratinocytes. BM damage and T‐cell migration in OLP may be mediated by matrix metalloproteinases (MMPs).

Kinetics of gene expression in murine cutaneous graft-versus-host disease.

The kinetics of gene expression associated with the development of cutaneous graft-versus-host disease (GVHD) were examined in a mouse model of MHC-matched allogeneic hematopoietic stem cell transplantation. Ear skin was obtained from recipient mice with or without GVHD between 7 and 40 days after transplantation for histopathological analysis and gene expression profiling. Gene expression patterns were consistent with early infiltration and activation of CD8(+) T and mast cells, followed by CD4(+) T, natural killer, and myeloid cells. The sequential infiltration and activation of effector cells correlated with the histopathological development of cutaneous GVHD and was accompanied by up-regulated expression of many chemokines and their receptors (CXCL-1, -2, -9, and -10; CCL-2, -5, -6, -7, -8, -9, -11, and -19; CCR-1 and CCR-5), adhesion molecules (ICAM-1, CD18, Ly69, PSGL-1, VCAM-1), molecules involved in antigen processing and presentation (TAP1 and TAP2, MHC class I and II, CD80), regulators of apoptosis (granzyme B, caspase 7, Bak1, Bax, and BclII), interferon-inducible genes (STAT1, IRF-1, IIGP, GTPI, IGTP, Ifi202A), stimulators of fibroblast proliferation and matrix synthesis (interleukin-1beta, transforming growth factor-beta1), and markers of keratinocyte proliferation (keratins 5 and 6), and differentiation (small proline-rich proteins 2E and 1B). Many acute-phase proteins were up-regulated early in murine cutaneous GVHD including serum amyloid A2 (SAA2), SAA3, serpins a3g and a3n, secretory leukocyte protease inhibitor, and metallothioneins 1 and 2. The kinetics of gene expression were consistent with the evolution of cutaneous pathology as well as with current models of disease progression during cutaneous GVHD.

Disease mechanisms in oral lichen planus. A possible role for autoimmunity.

Current evidence for the involvement of cell‐mediated immunological mechanisms in the pathogenesis of oral lichen planus is reviewed. Both a spatial and temporal relationship between cytotoxic T Lymphocytes and epithelial damage have been reported. Although keratinocytes appear to be the target for destruction in oral lichen planus, their role in antigen presentation is unclear. We propose that in oral lichen planus patients, diverse exogenous agents such as drugs, trauma and infection, stimulate the expression of a common self molecule by oral mucosal keratinocytes. An autoimmune reaction by cytotoxic T lymphocytes to these activated keratinocytes may result in the tissue destruction which is characteristic of oral lichen planus.

PHENOTYPE AND SUPPRESSOR ACTIVITY OF T-LYMPHOCYTE CLONES EXTRACTED FROM LESIONS OF ORAL LICHEN PLANUS

Lymphocytes were extracted from six biopsy specimens of oral lichen planus. T‐lymphocyte lines were expanded in culture with phytohaemagglutinin and interleukin 2, and cloned by limiting dilution. Fifteen T‐cell clones were isolated with a probability of clonality of 96.3%. The majority of clones (n=13) expressed the αβ T‐cell receptor, and of these, 11 were CD8+ and two were CD4+. Two clones were CD4− and CD8−, and expressed the γδ T‐cell receptor. The ability of these clones (effectors) to suppress concanavalin‐A‐stimulated proliferation of autologous lesional T‐cell lines (responders) was assessed. Maximum suppressor activity ranged from 17 to 100%. The majority of clones (n=12), including a CD3+ CD4+CD8−αβ+ clone, displayed suppressor activity which was proportional to the effector to responder ratio. A CD3+CD4+CD8−αβ+ clone and a CD3+CD4−CD8−γδ+ clone displayed substantial helper activity at higher effector to responder ratios. These results demonstrate differential helper and suppressor activity of T‐lymphocyte clones extracted from oral lichen planus lesions. The balance between help and suppression may be a fundamental determinant of immunological activity within the lymphocytic infiltrate of oral lichen planus, and hence may dictate the clinical behaviour of the disease.

Heat-Shock Protein Expression in Oral Epithelial Dysplasia and Squamous-Cell Carcinoma

Heat shock protein (HSP) expression is upregulated in tumour cells and, therefore, HSP expression is a likely marker of the malignant potential of oral epithelial lesions. Furthermore, the 70-kDa HSP (HSP 70) is implicated in the degree of tumour differentiation, the rate of tumour proliferation and the magnitude of the anti-tumour immune response. Accordingly, the distribution and intensity of HSP 70 expression was assessed in the epithelial compartment of oral squamous cell carcinoma (SCC, n = 29), dysplastic oral epithelium (n = 18) and benign oral mucosal lesions (n = 22) using avidin-biotin complex immunohistochemistry and microdensitometry under standardised conditions. Staining intensity was recorded in kilo-ohms (k omega). Normal oral mucosa (n = 15) was used for comparison, and results were analysed using Kruskall-Wallis and Fishers exact tests. The distribution of HSP 70 expression in well differentiated SCC was significantly different from that in poorly differentiated SCC (P < 0.05), the latter demonstrating a more focal staining pattern. Median staining intensity in SCC (6.22 k omega), epithelial dysplasia (9.61 k omega) and the benign oral mucosal lesions (8.28 k omega) was significantly greater than that in normal oral mucosa (5.64 k omega; P < 0.05). Staining intensity in poorly differentiated SCC (7.66 k omega) was greater than that in moderately differentiated SCC (4.77 k omega), although this result just failed to reach statistical significance (P = 0.06). These results suggest that, as employed currently, HSP 70 expression is not a definitive marker of oral malignancy or malignant potential.(ABSTRACT TRUNCATED AT 250 WORDS)

P. gingivalis-specific T-cell Lines Produce Th1 and Th2 Cytokines

Cytokines produced by T-cells in periodontal lesions may determine the nature of the adaptive immune response. Since different antigen-presenting cells (APC) may direct the Th1/Th2 response, P. gingivalis-specific T-cell lines were established by different APC subpopulations, and their cytokine profiles were determined. Peripheral blood mononuclear cells induced similar percentages of IL-4+ and IFN-gamma+ T-cells and lower percentages of IL-10+ T-cells. Epstein-Barr virus-transformed B-cells (LCL) induced higher percentages of IL-4+ cells than IFN-gamma+ cells, with lower percentages of IL-10+ cells. Peripheral blood mononuclear cells induced a higher percent of IFN-gamma+ CD8 cells than LCL (p = 0.004). Purified B-cells, monocytes, and dendritic cells induced similar percentages of IL-4+ and IFN-gamma+ cells, although again, the percentage of IL-10+ cells was lower. The results of the present study have demonstrated that, as measured by FACS analysis of intracytoplasmic cytokines, P. gingivalis-specific T-cells produce both Th1 and Th2 cytokines, regardless of the APC population.

Oral premalignancies and squamous cell carcinoma

Approximately 20% of oral squamous cell carcinoma (OSCC) cases arise without any identifiable environmental cause, suggesting involvement of genetic influences in their aetiology. DNA double-strand breaks (DSBs) sever both strands of DNA and pose a potential threat to genomic integrity. A hastened accumulation of somatic mutations consequent to DSB repair is deemed to be a likely event in tumorigenesis of OSCC.

Suppressor Cell Function in Oral Lichen Planus

Oral lichen planus (OLP) is a common inflammatory condition of the oral mucous membranes which affects between one and two percent of the general population. In accordance with the protracted clinical course of OLP and its association with known auto-immune diseases, the level of self-tolerance is questionable and possibly diminished in patients with this disorder. Normal suppressor T lymphocyte function is reputedly an essential element in the maintenance of self-tolerance, and deficient cell-mediated suppressor activity is implicated in the pathogenesis of auto-immune diseases. For assessment of in vitro cell-mediated suppressor activity in OLP, peripheral blood mononuclear cells (PBMC) from ten patients with OLP and from 11 control subjects were activated with the plant mitogen concanavalin A (Con A), followed by co-culture with autologous responder cells. The ability of irradiated Con A-activated cells to suppress the proliferation of Con A-stimulated responder cells was determined. Con A-induced suppressor activity of PBMC in the OLP patients was significantly less than that in control subjects (p = 0.001). Results of the present investigation complement previous in vitro findings which provided indirect evidence of deficient cell-mediated suppressor activity in OLP, particularly a decreased proportion of circulating CD4+CD45RA+ lymphocytes and reduced Con A-stimulated PBMC proliferation. The depressed Con A-induced suppressor activity of PBMC in the OLP patients provides direct evidence of deficient in vitro cell-mediated suppressor function in OLP, and suggests that defective cell-mediated suppressor circuits and reduced self-tolerance maybe involved in the pathogenesis of this disorder.