1. What is HLA-B27 HLA-B, the B site of human leukocyte antigen, is a product of human major histocompatibility complex (MHC) class I gene expressed on the surface of leukocytes, which can be detected by serological methods. It is known to have several isoforms, named in order HLA-B27O1, HLA-B2702… The positive detection rate of HLA-B27 in the normal population is 6-8% and is related to race, but in patients with ankylosing spondylitis, the positive rate is up to 90% or more. Clinical epidemiology and animal experiments have found it to be closely related to the development of seronegative spondyloarthropathies. 2, What are the HLA-B27 subtypes associated with the development of ankylosing spondylitis? Are there any racial differences? There are 26 HLA-B27 genetic isoforms with 24 encoded proteins identified. The distribution of HLA-B27 isoforms associated with ankylosing spondylitis is racially variable. 2705 is the predominant isoform in European and American whites, Mexican Americans, and Native Americans, followed by 2702. 2702 is found mainly in the Middle East and North Africa; 2703 has a low frequency and is found in a small number of West Africans and African Americans. The predominant subtype in Chinese, Thai, and Asian Indians is 27O4, followed by 2707. The association between different HLA-B27 subtypes and ankylosing spondylitis varies. It is currently believed that HLA-B2702, 2704, 2705 and the disease are positively correlated, and HLA-B2706, 2709 and the disease are negatively correlated. 3. What is the difference in clinical presentation between HLA-B27 positive and negative patients with ankylosing spondylitis? Although HLA-B27-negative and HLA-B27-positive ankylosing spondylitis share common clinical features, there are many differences: 1) HLA-B27-negative patients have a relatively late age of onset and a relatively late age of diagnosis 2) HLA-B27-positive patients have more acute iritis 3) HLA-B27-positive patients have a more pronounced family aggregation 4) HLA-B27-positive patients have more mid-axis (5) HLA-B27-positive patients are more likely to have hip pain and medullary arthropathy (6) HLA-B27-positive patients have more severe inflammatory changes, such as higher levels of erythrocyte sedimentation rate, C-reactive protein and other inflammatory indicators.