Association and frequency of HLA-A, B and HLA-DR genes in south Tunisian patients with spondyloarthritis (SpA)

The aim of this study is to investigate the association of HLA-A, B and HLA-DR gene expression and to assess an association of additional HLA antigens besides HLA-B27 in south Tunisian patients with spondyloarthritis (SpA). Eighty-five patients diagnosed with ankylosing spondylitis (AS, n = 68) and reactive arthrithis (ReA, n = 17) were selected and compared with 100 healthy controls (HC). HLA class I antigens were typed serologically using microlymphocytotoxicity technique. HLA-DRB1* alleles were studied by polymerase chain reaction amplification with sequence-specific primers. The significance of differences between patients and controls was tested by chi-square analysis. We found significantly increased frequencies of HLA-A3 (30.6%; pC = 0.04; OR = 2.95), HLA-B27 (62.35%; pC = 4.10⁻¹⁷, OR = 53.55), and HLA-DRB1*15 (17.2%; pC = 0.026; RR = 2.58) alleles in SpA patients compared to HC. The most frequent and strongest association was observed for HLA-B27 in AS (pC = 6.6 × 10⁻¹⁶, OR = 52.23). When AS and ReA patients were analysed separately, HLA-DRB1*15 and HLA-A3 were increased only in AS (pC = 0.01, OR = 2.99 and pC = 0.03, OR = 3.14, respectively). In ReA patients, HLA-DRB1*04 (p = 0.033, pC = NS, OR = 2.89) was found to be the most common allele. By analysing the HLA-B27-negative subgroup, HLA-A3 and HLA-DRB1*15 expression was found to be dependent on the presence of HLA-B27. HLA-B27 expression was higher in male (45/53; 85%) as compared to female (8/53; 15%) patients (p = 0.03). Apart from HLA-B27, HLA-A3 and HLA-DRB1*15 are the MHC class I and II alleles found most frequent in Tunisian patients with AS, whereas HLA-DRB1*04 was found most frequent in ReA patients. HLA-B27 is more frequent in male than in female patients.