Analysis of MHC encoded antigen-processing genes TAP1 and TAP2 polymorphisms in sarcoidosis

Sarcoidosis is a chronic granulomatous disease of unknown etiology. Several studies have suggested involvement of human leukocyte antigen (HLA) genes in sarcoidosis susceptibility. HLA associations described have not been consistent, possibly because of additional susceptibility genes adjacent to or within the major histocompatibility complex (MHC) such as genes for the transporter associated with antigen processing (TAP). The aim of this study was to analyze TAP gene polymorphisms in patients with sarcoidosis using the amplificatory refraction mutation system (ARMS) PCR. To determine whether any association between TAP gene variation and sarcoidosis was ethnic-independent we examined two European populations: 117 unrelated UK Caucasoid patients with sarcoidosis and 290 healthy UK control subjects, and 87 unrelated Polish Slavonic patients with sarcoidosis and 158 healthy Polish control subjects. We detected significant differences in TAP2 between the UK control and patient groups, and in TAP2 between the Polish control and patient groups. Comparing the UK and Polish control groups, we observed a difference in TAP1. Examination of HLA-DPB1 in our UK population showed no associations with disease or between variants at the TAP gene loci and HLA-DPB1 variants. These results suggest associations at the TAP loci occur independently of HLA-DPB1 associations, that TAP associations seen may be involved in determining sarcoidosis susceptibility, and that such susceptibilities differ between UK and Polish populations. This first study of TAP genes in UK and Polish sarcoid populations has demonstrated the importance of using multiple defined ethnic populations in defining the role genetic factors play in sarcoidosis susceptibility and the importance of candidate gene studies.