THE POSSIBLE RELEVANCE OF THE EXPRESSION OF MHC ANTIGENS AND OF EGF RECEPTOR IN AGGRESSIVE ORAL TUMORS

In this study the intensity of expression of major histocompatibility complex (MHC) class I and II antigens, adhesion molecule i.e. ICAM-1, epidermal growth factor receptor i.e. EGFr, T cell marker and cytokera tin were compared in oral squamous cell carcinoma (OSCC) and in the be nign ameloblastoma of the jaws. The results showed that: a) There was strong expression of both monomorphic and of polymorphic class I MHC a ntigens (90% of cases) in both basal and suprabasal cells of controls from normal mucose. b) Whereas up to 4% of OSCCs and 27% of ameloblast omas showed complete loss of monomorphic class I antigens, the frequen cy of polymorphic class I abnormalities was even more marked in both t umour types. c) Strong expression of class II MHC antigens and of ECFr was observed in the basal cells of most normal controls. d) Both clas s II (50% of cases) and ICAM-1 (30% of cases) showed strong expression in OSCC but not in ameloblastoma. The statistical values between OSCC and normal basal cells for class II and ICAM-1 were not significant w hilst the corresponding values for OSCC compared with ameloblastoma we re p<0.001 and p<0.001. In the case of OSCC, there were a large number of infiltrating T cells expressing activation marker i.e. class II an tigen. e) Strong expression of EGFr was seen in more than 90% of the O SCC cases compared with only 16% of ameloblastomas (0.01<p>0.001). Our working hypothesis to explain these abnormalities is that although bo th tumour types (more so in the case of ameloblastoma) have in place a n escape mechanism from the immune system, the overexpression of EGFr in OSCC may in part be responsible for the more aggressive behaviour o f the malignancy compared with the locally invasive but benign amelobl astoma.