HLA-B27

 

-Human Leukocyte Antigen: proteins that help the body’s immune system distinguish between body cells and foreign cells

 

B27 is a loci allele on chromosome 6 in the MHC. The function of HLA-B27 is to bind antigenic peptides and present them to cytotoxic T lymphocytes. The association of HLA-B27 and seronegative spondyloarthropathies, such as Ankylosing Spondylitis, has been studied for at least 25 years, but there is no concrete answer for the relationship between them. Benjamin and Parham believe that certain subtypes of HLA-B27 may predispose an individual to AS by bonding certain ‘arthritogenic’ peptides that then create ‘arthritogenic’ lymphocytes. This hypothesis would account for the variation seen in the association of HLA-B27 and AS in individual populations as B27 subtypes vary.

                                                        Theories explaining the association of HLA-B27 and                                                                       Spondyloarthropathies (Bowness 858)

 

-HLA-B27 is in genetic linkage with a disease associated gene

-HLA-B27 binds and presents ‘arthritogenic’ peptides to T       cells

-HLA-B27 is involved thymic selection of a T-cell repertoire that is         susceptible to spondyloarthritis

-HLA-B27 has an unusual cell biology compared with other      HLA class 1         molecules

        -The HLA-B27 free cysteine at position 67 can be   modified, leading to an         ‘altered self’

        -There is cross reactivity between antibodies directed at bacterial protein(s) and  HLA-B27

        -HLA-B27 is a receptor for a bacterial ligand

        -Interaction of HLA-B27 with a bacterial superantigen     causes non-specific T-cell stimulation

        -HLA-B27-derived peptides are presented by HLA class 2                        (6)                                 molecules to CD4+ T cells

 

                                                                                                                                HLA-B27 has been linked to other diseases, such as inflammatory bowel disease, psoriatic arthritis, aortic regurgitation and anterior uveitis, in addition to ankylosing spondylitis. Inflammatory bowel disease and anterior uveitis are often presented as symptoms of ankylosing spondylitis, though the relationship may simply be the increased incidence of all 3 diseases in individuals with certain HLA-B27 subtypes.