COMEDK 2007 MCQ Answer 71

The correct answer is B


The spondyloarthropathies are a family of interrelated, but heterogeneous, conditions. There can be a marked overlap between the different conditions. All of these conditions are associated to a greater or lesser extent with the HLA B27 antigen. The diseases included in this group are ankylosing spondylitis, Reiter’s syndrome, reactive arthritis, psoriatic arthritis, and the enteropathic arthritis associated with inflammatory bowel disease.

Disease classified under the spondyloarthropathies

• Ankylosing spondylitis (AS)
• Reiter’s syndrome / Reactive arthritis
• Enteropathic arthritis (Crohn’s disease, ulcerative colitis)
• Psoriatic arthritis

Although the precise etiology is unknown, there is a strong association between this group of diseases and the HLA-B27 antigen. HLA-B27 forms part of the class I antigens of the major histocompatibility complex (MHC) and is expressed on the surface of many cell types. This supports the view that these diseases are due to a genetically determined immune response to environmental factors.

One hypothesis is that an immune response is triggered by an infection in the gastrointestinal or genitourinary tracts. Some Chlamydia, Salmonella and Yersinia antigens can be found in the synovial fluid of patients who had infections with these pathogens. Some peptide fragments from these bacteria possibly bind to the HLA-B27 antigen and are presented to the T-cells, thus triggering an autoimmune response.

An alternative hypothesis suggests an autoimmune reaction to self-antigens, because of mimicry between fragments of the infecting microorganisms and host tissue i.e. antigenic fragments between fragments of bacteria and self-antigens. These infecting organisms may be Gram negative bacteria, such as Klebsiella which have been shown to possess antigens that resemble the HLA-B27 antigen. They may give rise to antibodies that crossreact and bind to HLA-B27 positive cells resulting in disease manifestations.