The results were collected, tabulated, and statistically analyzed by IBM personal computer and statistical package SPSS version 18 (SPSS Inc., Chicago, Illinois, USA). Descriptive statistics as mean and SD for continuous data, and frequency and percentage for discrete data were used. Analytic statistics such as t-test was used to study comparison between two continuous parametric data, while analysis of variance test was used to study comparison between more than two continuous data. P values less than 0.05 were considered significant.
The OLP group included 20 patients, 10 male patients and 10 female patients with a mean age of 51.55±10.53 years. The healthy control group included 11 male individuals and nine female individuals with a mean age of 48.36±9.48 years. The HCV positive group ‘without OLP’ included eight male patients and 12 female patients with a mean age of 50.31±11.24 years. All groups were matched as regards age and sex. The clinical data of the OLP group is summarized in Table 1. According to HCV serodiagnosis, 12 cases of OLP were HCV positive and eight cases were HCV negative.
The MFI of expressed TLR2 on PBMCs tended to be higher in the HCV positive OLP cases (28.08±5.64) than in the HCV negative OLP cases (25.02±3.1). However, the difference does not reach statistical significance (P=0.18) (Table 3).
There were nonsignificant associations between TLR2 expression levels in the OLP group and site, type and duration of the lesions and presence of skin lesions (P=0.33, 0.47, 0.75, and 0.13, respectively). There were also nonsignificant associations between TLR2 expression levels and age and sex of OLP patients (P=0.49, 0.16, respectively).
To our knowledge, this is the first study that compared TLR2 expression levels on PBMCs between HCV positive OLP patients, HCV negative OLP patients, HCV positive patients without OLP and healthy volunteers. We also examined a possible association between OLP and HCV infection and their relationship with the expression levels of TLR2.
TLR2 expression has been found in human cells and tissues in a resting state or after activation 10. Sabroe et al.11 reported positive TLR2 expression on normal PBMCs. In the current study, significant higher levels of TLR2 expression on PBMCs were found in OLP patients and HCV positive ‘patients without OLP’ than in normal subjects, and the intensities of expression were not correlated with different clinical types or sites of OLP, which is consistent with the study of Ohno et al.7.
The mechanism(s) that lead to upregulation of TLR2 expression on PBMCs of OLP patients remains unclear. Various studies have reported that, under certain conditions, PAMPs and cytokines upregulate TLR2 expression in a variety of cells 12,13. The serum cytokine levels were more elevated in OLP patients than in normal individuals 14. Moreover, the PBMCs of OLP patients produce considerably higher amounts of proinflammatory cytokines than that produced by PBMCs of normal individuals 7.
The modulation in TLR2 expression on PBMCs may be involved in the pathogenesis of OLP. Previous data suggested that OLP is a T-cell-mediated autoimmune disease in which autocytotoxic CD8+ T cells trigger apoptosis of oral epithelial cells 15. How are these autocytotoxic CD8+ T cells induced into the lesions of OLP? In cases of OLP, activation of TLR2 on PBMCs leads, via different intracellular signaling pathways, to the production of proinflammatory stimuli, immune-regulatory cytokines, chemokines and costimulatory molecules, and is considered a danger signal that should transform the skin into the functional state of defense 16. Overexpression of TLR2 on PBMCs in patients with OLP results in overproduction of IL12 7. IL12 is an important cytokine that induces Th1 cell differentiation. Th1 cell cytokines promote cytotoxic lymphocyte and NK cell responses and are also linked to the development of autoimmunity 17. It might be proposed that, the shift of the Th1/Th2 balance toward Th1 dominance in OLP patients, probably depends on the upregulation of TLR2 expression 7.
HCV is a global health challenge. Egypt has the highest HCV prevalence in the world, 14.7% 18–20. An association between HCV infection and OLP has been recognized. The pathogenesis of such association is still unclear. It may be due to cell-mediated cytotoxicity to an epitope shared by HCV and damaged keratinocytes. Virus replication in the oral epithelium may also contribute directly to the development of lesions. Moreover, the high mutation rate of the virus may result in repeated activation of immune cells, increasing the probability of cross-reaction with its own tissue and, consequently, the risk of autoimmune disease 21,22.
Whether HCV-infected patients have increased risk of developing OLP or patients with OLP have enhanced risk of developing HCV infection is yet to be answered 23. Early studies 24,25 have suggested that HCV may persist and replicate in the diseased oral mucosa, but later studies 21,26 have shown no HCV transcripts in the epithelium of OLP lesions. Moreover, the value of antiviral treatment effective against HCV has not been proven in OLP patients; there are many reports 27,28 of interferon inducing or aggravating OLP. In the present study, we found no statistical difference between HCV positive OLP patients (60%) and HCV negative OLP patients (40%) that may suggest lack of increased risk of OLP in HCV-infected patients. However, the small size of the study may limit this suggestion.
Various studies have proposed a role for TLR signaling in the pathogenesis of HCV. TLR2 and TLR4 expression have been assessed on monocytes of HCV-infected patients in several studies. HCV may signal directly through TLR2 by core protein and nonstructural protein 3, or indirectly through alternative TLRs, for example, TLR4, 29,30 leading to increased inflammatory cytokines such as TNF-αthat cause hepatocyte damage. Our results were consistent with previous studies that reported increased TLR2 expression on PBMCs during HCV infection ‘without OLP’ 29–31.
In accordance with the immune modulation that occurs in OLP, HCV infection modifies the innate immune system by upregulating the expression of TLR2 that could increase the production of downstream cytokines. Increasing the production of related inflammatory and regulatory cytokines increases the risk of immunopathology and exerts an indirect effect in the pathogenesis of OLP 20,30. However, in our study, we detected a nonsignificant difference between the expression of TLR2 in HCV negative OLP and HCV positive OLP patients. Thus, we believed that, in OLP patients, HCV coincidence may have no additive effect on the expression level of TLR2 on monocytes. To date, there are no published reports about TLR2 expression in OLP associated with HCV infection.
To summarize, oral epithelial cell apoptosis and hepatocyte damage are hallmarks in OLP and HCV infection, respectively. TLR2 expression increased in OLP and HCV infection ‘without OLP’. Overexpression of TLR2 induces Th1 cell differentiation, which promotes cytotoxic lymphocytes and proinflammatory cytokines, which induce oral epithelial cells apoptosis and hepatocyte damage.
We concluded that, the increased TLR2 expression on PBMCs is probably involved in the pathogenesis of OLP with or without HCV infection, as well as in the pathogenesis of HCV infection ‘without OLP’. The idea that TLR2 can be the gate by which HCV induces OLP cannot be verified by this study. Our study supports a critical role for ‘TLR2 – immune‘ interaction in the pathogenesis and maintenance of OLP. Further studies are required to evaluate TLR2 and other TLRs’ expression after treatment of OLP and the possibility to be a therapeutic target in this resistant and progressive disease. Studies to clarify whether HCV infection has a role in OLP or whether it is merely an association are also recommended.
There are no conflicts of interest.
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