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Oral lichen planus (OLP) is a chronic inflammatory disease of the oral mucosa and also one of the more common mucosal conditions mostly affecting middle aged individuals. Even though OLP is well investigated the etiology of this disease is still unknown, even if autoimmunity as a possible etiologic factor has been suggested. WHO classifies OLP as a pre malignant condition but malignant transformation of OLP is a matter of great controversy. The p53 protein is a tumour suppressor with the potential to induce apoptosis or cell cycle arrest of DNA damaged cells. Another member of the p53 family, p63, comprises six different isoforms, and plays a crucial role in the formation of oral mucosa, salivary glands, teeth and skin. p63 has also been suggested to be involved in development of squamous cell carcinoma of the head and neck (SCCHN). β-catenin, E-cadherin and epidermal growth factor receptor (EGFR) are p63 related proteins and abnormalities in their expression are suggested to be involved in development of SCCHN.

Methods. Using immunohistochemistry and antibodies directed against p53 and those distinguishing between the p63 isoforms we analysed biopsies of OLP, SCCHN and normal oral tissue. We also mapped levels of p63 and p53 isoforms using RT-PCR technique. Furthermore expression of the p63 related proteins β-catenin, E-cadherin and EGFR was studied using immunoblot analysis. In an attempt to investigate autoimmunity as a causative factor of OLP we analysed sera from patients diagnosed with OLP and matched control individuals in order to see if there were autoantibodies directed against the p53 family.

Results. When mapping p53 and p63 protein status decreased expression of p63 and increased expression of p53 was seen in OLP compared to normal tissue. In accordance with these results, levels of p63 RNA were also lower in OLP lesions compared with normal tissue. Concerning p53 isoforms, the “original” p53 isoform was expressed in all OLP lesions and normal control tissue. Of the other isoforms, p53β and Δ133p53 were expressed in the majority of samples. Our results regarding p63 related proteins showed a generally lower expression of these proteins in OLP lesions compared to normal control tissue. When studying sera from patients with OLP we found circulating autoantibodies against all six p63 and four p73 isoforms in two patients.

Conclusions. The potential for malignant transformation of OLP is still a subject of discussion and rather controversial. While some of our results regarding status of p53 and p63 both at protein and RNA levels support this theory, other results concerning for example p63 related proteins point in the opposite direction. Based on our studies it is thus not possible to either support nor contradict the statement that OLP is a clear-cut premalignant condition. In our effort to understand the etiology of OLP we were the first to demonstrate autoantibodies against p63 and p73 in what could be a subgroup of OLP patients. OLP could thus be suggested to be not one distinct disease, but based on our data a disease comprising different subgroups.