Elucidating the role of Cyclooxygenase‐2 in the pathogenesis of oral lichen planus – an immunohistochemical study with supportive histochemical analysis

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Oral lichen planus (OLP) is a chronic, inflammatory disorder that affects the oral mucous membrane 1. Although OLP may occur in all the age groups, it is usually reported between the 3rd and the 6th decade of life 2. It generally affects about 1–2% of the population, with a slight difference in its prevalence rate between varied ethnicities 3. Women are affected more commonly than men in a ratio of 1.4:1 5.
The histopathological criteria set by the WHO for the diagnosis of OLP include liquefactive degeneration of the basal cells, colloid bodies, homogenous infiltration of lymphocytes in a dense, band‐like pattern along the epithelial connective tissue interface, cytological normal maturation of the epithelium, saw‐tooth rete ridges and hyperpara/orthokeratosis 6.
During the inflammatory response, several chemokines such as IL‐1, IL‐6, IFN‐α are released by the epithelial cells. An increased level of these cytokines is evident in OLP, which emphasizes the importance of these mediators in its etiopathogenesis 7. While some authorities consider OLP to be an autoimmune disorder, the others attribute it to a T‐cell‐mediated immune response. An association between deregulated immune function in response to the inflammatory reaction in OLP is well known 9.
Cyclooxygenase 2 is a 72‐Kda inducible enzyme that is involved in the biosynthesis of prostaglandin 10. COX‐2 is induced in response to growth factors, hormones and cytokines 11. COX‐2 converts arachidonic acid to five different primary prostanoids, which have several biological functions 12. Several studies have demonstrated an upregulation of COX‐2 in OLP 13.
A number of studies have demonstrated an increase in the mast cell density and mast cell degranulation in OLP 8. A host of preformed as well as newly synthesized cytokines and chemokines, including the TNF‐α, has shown to be secreted by the degranulating mast cells. These mediators are known to activate T cells and trigger the activation of matrix metalloproteinases (MMPs) by the lesional T cells. Activation of MMPs, along with mast cell‐derived chymase and tryptase, degrades the basement membrane structural proteins, resulting in basement membrane breaks 17.
The aim of the study was to evaluate and correlate the expression of COX‐2 with the severity of mast cell deregulation and the ensuing basement membrane disruption in oral lichen planus. A better understanding of this distinctive cycle may aid in developing effective treatment strategies to combat this enigmatic disorder.

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