Genes coding for HLA have been considered as possible markers of periodontitis, as they are involved in the regulation of immune responses, several studies have evaluated this association, and despite the inconclusive results, HLA-A9 and -B15 antigens have been most commonly associated with high susceptibility to AP and HLA-A2 and -B5 antigens have been considered protective. Ethnicity is an important variable to consider in assessing susceptibility to the disease. The purpose of the present study was to: 1) evaluate the association of HLA-B15 and HLA-B5 with AP and 2) propose some pathophysiological hypotheses to try to explain the role of the HLA molecule in the pathogenesis of AP.