ABSTRACT
<p><b>OBJECTIVE</b>The purpose of this study was to examine the expression of human major histocompatibility complex-I at different degrees of dysplasia leukoplakia, and to investigate local immune status and discuss their associations with oral leukoplakia.</p><p><b>METHODS</b>The monoclonal antibody of MHC class I antigen was employed in this study. There were 55 oral leukoplakias, 31 primary oral squamous cell carcinomas and 28 histologically normal oral epithelia were detected for the presence of the MHC class I molecule by using immunohistochemistry method.</p><p><b>RESULTS</b>The MHC class I antigen expression of the severe dysplasia and oral squamous cell carcinoma was significantly lower than that of the normal epithelia (P < 0.05). But their expression did not show statistically difference between the normal epithelia and other groups of oral leukoplakia (P > 0.05).</p><p><b>CONCLUSION</b>The expression levels of the MHC class I antigen is reduced in oral leukoplakia, particularly in severe dysplasia oral leukoplakia, it is relevant to the degree of dysplasia.</p>