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 Table of Contents  
Year : 2014  |  Volume : 1  |  Issue : 3  |  Page : 143-147

Mast cell - Melanocyte axis mediates pathogenesis in Oral Lichen Planus

Department of Oral and Maxillofacial Pathology, Dr. Syamala Reddy Dental College, Hospital and Research Centre, Marathalli, Bangalore, Karnataka, India

Date of Web Publication8-Dec-2014

Correspondence Address:
Venkatesh Vishwanath Kamath
Department of Oral and Maxillofacial Pathology, Dr. Syamala Reddy Dental College, Hospital and Research Centre, Marathalli, Bangalore, Karnataka
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/2348-2915.146493

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Background: Oral Lichen Planus (OLP) is a cell-mediated inflammatory condition of the oral cavity with propensity for malignant transformation. Often classified as an autoimmune disorder, the pathogenesis of the lesion is still under debate. The presence of mast cells (MCs) and melanocytes (MNs) has been identified as an integral part of the cellular reaction in all stages of the disorder. Aims: The present study aims to qualify, localize and quantify MCs and MNs in OLP and normal oral mucosa (NOM) using special stains and image analysis software. Computations and correlations between the numbers and localization of the cells in different layers of the tissue were done.Materials and Methods: Thirty cases of OLP and 10 cases of NOM were included. MCs were identified by their metachromasia using Toluidine blue and the MNs by Masson's Fontana stain. A localization and quantification of the numbers of the two cell groups was done by image analysis and statistically correlated by two sample t-test. Results: The total count of mast cells and melanocytes was more in OLP in comparison to that of NOM. The MCs were present in the deeper tissues in contrast to MNs which were localized only to the basal and sub-basal areas. MNs appeared to proliferate and migrate to the subepithelial areas in OLPs in contrast to their strong localization to the basal layer in NOM. The ratio of MCs/MNs was higher in OLP compared with NOM. Interestingly the toluidine blue stain showed cross-sensitivity in expression of both MCs and MNs in OLP. Conclusion: MCs and MNs are expressed in increased numbers in OLP and probably have a synergistic mode of action in the pathogenesis of the disorder. The spilling out of MNs in OLP to the sub-basal areas is consistent with the clinical observation of pigmentation in healed/under remission OLP cases.

Keywords: Auto-immune disroder, mast cells, melanocytes, pathogensis, oral lichen planus

How to cite this article:
Rajkumar K, Kamath VV, Lavanya RM. Mast cell - Melanocyte axis mediates pathogenesis in Oral Lichen Planus. J Dent Res Rev 2014;1:143-7

How to cite this URL:
Rajkumar K, Kamath VV, Lavanya RM. Mast cell - Melanocyte axis mediates pathogenesis in Oral Lichen Planus. J Dent Res Rev [serial online] 2014 [cited 2022 Dec 8];1:143-7. Available from: https://www.jdrr.org/text.asp?2014/1/3/143/146493

  Introduction Top

Oral lichen planus (OLP) is a potentially malignant disorder seen in 1-2% of the general population. It is a chronic cell-mediated inflammatory condition affecting the oral mucosa in response to an induced antigenic change. Mast cells are known to play a role in its pathogenesis by directing T cells subepithelially maintaining the chronicity of the condition. [1]

Mast cells (MCs) are mobile, bone-marrow derived cells that are seen in connective tissue especially near the blood vessels. [2] They contain numerous intracytoplasmic granules which are liberated on stimulation. When observed under light microscopy, the secretory granules show an intense staining reaction with basic aniline dyes. [3] Increase in mast cells counts were reported in OLP. [1],[4]

Melanocytes (MNs) are highly motile dendritic cells of neural crest origin situated in the stratum germinativum. Cytoplasm of melanocytes contains melanin pigment that is packed in small granules termed melanosomes. [5] Argentaffin methods like Masson Fontana techniques may be used to stain melanin but are not specific for melanocytes. [6] Melanin pigmentation is usually not pronounced in the buccal mucosa, tongue, palate or gingiva. [5] Melanin associated pigmentation was reported in the course of inflammatory conditions including oral lichen planus. [7],[8] This pigmentation is attributed to pigmentary incontinence or as defence mechanism to antigens. [9],[10]

Mast cells and melanocytes might share a common mesoectodermal stem cell origin and existence of a histogenetic relationship between the two had been proposed in the past. Numerous findings supporting this were reported. [11],[12],[13]

The aim of the study was to compare MC and MN counts in OLP to normal oral mucosa and to study the relationship between the MCs and MNs especially in terms of localization in the tissue.

  Materials and Methods Top

Thirty cases of OLP and 10 cases of normal oral mucosa (NOM) were included in the present study. Five micron paraffin sections were obtained and stained with hematoxylin-eosin (H and E), Mason Fontana and toluidine blue (Wolman's method, 1971).

The sections were then analysed with an image analyser (ProReg Capture ® 2012). Counting for MCs was done in subepithelial and in deeper connective tissue and MNs were counted in basal layer and in subepithelial locations respectively. A digital grid was used for cell counting and at each location, cells were counted in three different areas and the mean of each was taken and subjected to statistical evaluation.

The results were statistically analysed using two sample t-test.

  Results Top

Granules in MCs showed metachromasia appearing purplish and the nucleus stained blue [Figure 1]. Few of the cells/granules in the basal layer and in sub epithelial areas of normal mucosa and OLP stained greenish black [Figure 2] and nucleus stained blue [Figure 3]. These corresponded to the location of melanocytes/melanosomes observed in H and E and Mason Fontana stained sections, an indication that there was cross-sensitivity of the toluidine blue stain in terms of expression in melanocytes and mast cells [Figure 4]. The quantification of the MCs and MNs were analysed statistically.
Figure 1: Photomicrograph of OLP showing subepithelial melanocytes (arrows). (a. H and E; b. Masson-Fontana; c. Toluidine blue x10, original magnification)

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Figure 2: Photomicrograph of OLP showing mast cells in deeper connective tissue (arrows) (Toluidine blue x10 original magnification)

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Figure 3: Photomicrograph of OLP showing melanocytes stained with toluidine blue-dark green (left) and Masson-fontana stain (brown-black) (right) indicative of cross-sensitivity owing to emryological origin. (×40 original magnification)

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Figure 4: Photomicroraph of OLP showing close relation between melanocytes and mast cells in the subepithelial region (Tpluidine blue ×40 original magnification)

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Statistical analysis

Two sample t-test was applied for statistical evaluation (SPSS software v. 16, 2012). A significant increase in total MC count in OLP compared to that of normal oral mucosa [Table 1] was observed. This increase was found both in the subepithelial and in deeper connective tissue in OLP. In OLP, MC count was significantly higher in deeper connective tissue as compared to that in subepithelial area. In NOM, no significant difference in MC count was noted between the two areas [Table 2].

Total MN count was higher in OLP than in NOM but the finding was statistically not significant [Table 3]. No difference in MN count between basal layer and subepithelial areas in OLP. However in NOM, significant difference in MN count between the two areas was noted. Significant increase in MN count was observed in subepithelial area of OLP [Table 4]. The ratio of mast cells to melanocytes was higher in OLP compared to that in NOM, however this finding was statistically not found to be significant [Table 5].
Table 1: Comparison of mast cell counts in oral lichen planus to that of normal oral mucosa cases

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Table 2: Comparison of mast cell count of OLP and NOM in subepithelial area to that in deeper connective tissue areas

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Table 3: Comparison of melanocyte count in oral lichen planus to that of normal oral mucosa cases

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Table 4: Comparison of melanocyte count of OLP and NOM in basal layer to that in subepithelial area

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Table 5: Comparison of both mast cell count to melanocyte count individually in OLP and NOM cases

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  Discussion Top

OLP is a chronic disorder of the oral tissues with auto-immune manifestations. Apart from the debility it causes to the afflicted individuals, its potential for malignant transfromation is most alarming. In addition the association of the disorder with dental restorative materials like amlagam and drugs are reasons the average medical and dental practitioner encounters them more frequently in daily practice.

The role of mast cells in the disorder has been recognised in the past. Increased MC counts and release of mast cell mediators in OLP are thought to promote basement membrane disruption and further maintain the chronicity of the condition by recruiting more number of T-lymphocytes subepithelially. The present study showed overall increased MC counts in OLP which is in accordance with the previous reports suggesting mast cell role in maintaining the chronicity of the condition. [1] The sublocalization of the MCs was done to assess their presence in the tissues vis-ΰ-vis other cellular components and to specifically correlate them with the number and locale of the MNs. Higher mast cell numbers in the deeper connective tissue observed here is probably related to the increased vascularity of the locale. The obvious lack of melanocytes in this area is indicative of the origin of the two cell groups: MCs from connective tissue and MNs from the epithelium. The migration of the MCs to the upper layers of the connective tissue is coincided by the downward migration, albeit limited, of MNs to the sub basal/juxta-epithelial layers.

Melanin pigmentation in OLP is a frequent clinical occurrence, especially those involving steroid medication, healed or in-remission cases. In the present study we noted an increase in melanocyte count subepithelially in OLP as compared to that in NOM. It was suggested that melanocytes in OLP are stimulated by the cytokines released by the subepithelial inflammatory infiltrate. [8] This is plausible especially in view of the fact that a juxtaepithelial band of inflammatory infiltration is a pathognomic histological feature of OLP and the melanocytic proliferation is seemingly restricted in this region. The present study also noted increased mast cell to melanocyte counts in OLP. Further in subepithelial location, mast cells and melanocytes were found to be in close relation [Figure 4].

The mast cell-melanocyte axis has an embryonic derivation. Two types of cells exist in the migrating cephalic neural crest, cells which are restricted towards a specific differentiation pathway and those cells with pleuripotential capacity from which neuronal and mesoectodermal derived cell-types differentiate. Environmental factors might influence the differentiation pathway of these committed and totipotent stem cells. [14]

Stem cell factor (SCF) also called as mast cell growth factor is the pleiotropic ligand for the tyrosine kinase receptor, c-kit. C-kit ligand and receptor are usually expressed in different cell types, and binding of SCF to c-kit promotes cell proliferation, differentiation, and recruitment of progenitor cells in various biologic systems. [15] In vitro studies showed that SCF can promote survival and differentiation of hematopoetic lineages. Mast cells are the only hematopoetic cells that retain significant capacity to express stem cell factor receptor. SCF affects melanocyte and mast cell growth, survival, secretion and adhesion as well as migration into tissues. [16],[17],[18] [Table 6].
Table 6: Depiction of histogenetic relationship of mast cells to melanocytes based on observations from Okun MR, Galli SJ, Baroffio A[11,14,16]

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The role of SCFR in proliferation of mast cells and melanocytes has been previously reported. SCFR expressed by mast cells might stimulate melanocytes. Studies provided evidence for increased mast cell numbers being associated with hyper pigmentation and other melanocytic tumors. [19],[20] A similar mechanism seems to be at play in OLP. Known or unknown antigenic stimuli initiate expression and liberation of SCF which in turn determines the mast cell and melanocyte response in OLP. The liberation of the contents of the two cell groups probably plays a part in the clinical and histological manifestations of the lesions. Thus the mast cell-melanocyte axis is probably an integral part of the pathogenetic mechanisms of OLP [Table 7]. This supposition was also bolstered by the histological observation in the present study, that toluidine blue, a specific metachromatic stain for secretory granules of mast cells was found to express cross-sensitivity and stain melanocytes as well [Figure 2].
Table 7: The mast cell - melanocyte axis in the pathogenesis of OLP

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Secretory granules of mast cells produce a characteristic metachromatic staining pattern with toluidine blue. [2] The metachromatic color is due to selective staining of different tissue components to different colored substances. [21]

Differential staining of melanosomes (of dark green color, [Figure 2]) observed in the present study might be because of either of the following reasons:

  1. Melanosomes possibly show metachromasia property since both mast cells and melanocytes share a common metabolic pathway (of peroxidase activity in melanin synthesis) and are histogenetically related [13]
  2. those are probably not melanosomes but are infact mast cell granules which have transformed to melanin [22],[23] or
  3. those are mast cells which have phagocytosed melanin granules. [23]

The first explanation is more likely plausible here, since not only the melanosomes in the subepithelial area but also all the melanosomes in the basal layer stained dark green. Further no cells in the deeper connective tissue (where increased mast cell count was noted) showed such staining characteristics.

  Conclusion Top

Increased mast cell count is a consistent finding in OLP making it a prominent component of the inflammatory infiltrate. The present study observed an increased mast cell- melanocyte count in OLP in comparison with NOM and a definite correlation of the two cell groups. A probable mast cell-melanocyte axis being an integral part of the pathogenetic mechanisms of OLP is proposed based on the above observations.

  References Top

Zhao ZZ, Savage NW, Sugarman PB, Walsh LJ. Mast cell/T cell interactions in oral lichen planus. J Oral Pathol Med 2002;31:189-95.  Back to cited text no. 1
Walsch LJ. Mast cells and oral inflammation. Crit Rev Oral Biol Med 2003;14:188-98.  Back to cited text no. 2
Berkovitz BK, Holland GR, Moxham BJ. Oral mucosa. In: Parkinson M, editor. Oral Anatomy, Histology and Embryology. 3 rd ed. London: Mosby; 2002. p. 195.  Back to cited text no. 3
Theoharides TC, Cochrane DE. Critical role of mast cells in inflammatory diseases and the effect of acute stress. J Neuroimmunol 2004;146:1-12.  Back to cited text no. 4
Berkovitz BK, Holland GR, Moxham BJ. Oral mucosa. In: Parkinson M, editor. Oral Anatomy, Histology and Embryology. 3 rd ed. London: Mosby; 2002. p. 226.  Back to cited text no. 5
Barret AW, Raja AM. The immunohistochemical identification of human oral mucosal melanocytes. Arch Oral Biol 1997;42:77-81.  Back to cited text no. 6
Durmisova A, Balabanova M. Melanocytic population of buccal mucosa of patients with lichen planus. Indian J Dent Res 2001;12:175-9.  Back to cited text no. 7
Mergoni G, Ergun S, Vescovi P, Mete Ö, Tanyeri H, Meleti M. Oral postinflammatory pigmentation: An analysis of 7 cases. Med Oral Patol Oral Cir Bucal 2011;16:e11-4.  Back to cited text no. 8
Cawson RA. Treatment of oral lichen planus with betamethasone. Br Med J 1986;1:86-9.  Back to cited text no. 9
Heera R, Kamath VV, Shasthri KA. A histological evaluation of melanosis in oral epithelial dysplasia. Indian J Oral Pathol 1991;1:20-3.  Back to cited text no. 10
Okun MR. Mast cells and melanocytes. Int J Dermatol 1976;15:711-22.  Back to cited text no. 11
Okun MR, Donnellan B. Ultrastructural relationship of melanocytes to mast cells and "melanophages" in a lesion of alopecia mucinosa. J Invest Dermatol 1972;59:211-24.  Back to cited text no. 12
Okun MR, Edelstein LM, Or N, Hamada G, Donnellan B. The role of peroxidase vs. the role of tyrosinase in enzymatic conversion of tyrosine to melanin in melanocytes, mast cells and eosinophils. J Invest Dermatol 1970;55:1-12.  Back to cited text no. 13
Barofflo A, Dupin E, Le Douarin NM. Common precursors for neural and mesectodermal derivatives in the cephalic neural crest. Development 1991;112:301-5.  Back to cited text no. 14
Gagari E, Rand MK, Tayari L, Vastardis H, Sharma P, Hauschka PV, et al. Expression of stem cell factor and its receptor, c-kit, in human oral mesenchymal cells. Eur J Oral Sci 2006;114:409-15.  Back to cited text no. 15
Galli SJ, Costa JJ. The regulation of mast cell development, survival and function in vivo by stem cell factor, the ligand for the c-kit receptor: Clinical implications. New Trend Allergy 1997;23:151-8.  Back to cited text no. 16
Yamamoto, Katayama I, Nishioka K. Role of mast cells in dermatofibroma: Recent viewpoints into the pathogenesis. Eur J Dermatol 2003;13:419-23.  Back to cited text no. 17
Grabbe J, Welker P, Dippel E, Czarnetzki BM. Stem cell factor, a novel cutaneous growth factor for mast cells and melanocytes. Arch Dermatol Res 1994;287:78-84.  Back to cited text no. 18
Schadendorf D, Kohlmus C, Gawlik C, Suter L, Czarnetzki BM. Mast cells in melanocytic tumours. Arch Dermatol Res 1995;287:452-6.  Back to cited text no. 19
Woringer F. Mastocytes and cutaneous pigmentation. Bull Soc Fr Dermatol Syphiligr 1955;62:31-4.  Back to cited text no. 20
Kramer H, Windrum GM. The metachromatic staining reaction. J Histochem Cytochem 1955;3:227-37.  Back to cited text no. 21
Okun MR. Pigment formation in mast cells in tissue culture. J Invest Dermatol 1967;48:424-8.  Back to cited text no. 22
Sato S, Kukita A, Sato SI. Phagocytosis and degradation of melanosomes by the mast cells. J Invest Dermatol 1969;53:183-6.  Back to cited text no. 23


  [Figure 1], [Figure 2], [Figure 3], [Figure 4]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]


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