HLA molecules, bacteria and autoimmunity

It has been well established that many diseases are linked to HLA antigens, Two of the most interesting HLA associations may provide some insight into the pathogenesis of rheumatic inflammatory conditions. In ankylosing spond ylitis (AS), 96% of patients possess HLA-B27, whilst the frequency of this marker in the general population is c, 8%, In rheumatoid arthritis (RA), >9 0% of patients possess either HLA-DR1 or some subtypes of HLA-DR4, whilst t he frequency of this marker in the general population is c, 35%, The associ ation between HLA-B27 and reactive arthritis (ReA) has also been well estab lished. Furthermore, it has been shown that ReA is triggered by infection v ia the gastrointestinal tract due to Yersinia, Salmonella or Campylobacter spp, and in the genitourinary tract due to chlamydia, In a similar way, mic robiological and immunological studies have revealed an association between Klebsiella pneumoniae in AS and Proteus mirabilis in RA, This article revi ews the possible pathological implications of the associations between HLA- B27, K, pneumoniae and AS, as well as HLA-DR1/DR4, P. mirabilis and RA.