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Group A Streptococcus is a common bacterium that induces tonsillitis, pharyngitis, and pyoderma, and, furthermore, its metabolic products cause scarlatina. It is suggested that the molecular mimicry and cross reactivity between human tissues and the micro-organism are associated with immunogenic pathogenesis of well known post-streptococcal manifestations: acute rheumatic fever and acute glomerulonephritis.1,2 Recently, non-purulent arthritis after or during streptococcal infection, HLA-B27 unrelated “post-streptococcal reactive arthritis (PSReA)”, has been reported as another manifestation associated with streptococcal infection.3–5 The pathogenesis of PSReA is unknown, but it is likely that it is an immunogenic disorder similar to acute rheumatic fever.
Anticardiolipin antibodies (aCL) are often detected in patients with autoimmune diseases, especially systemic lupus erythematosus, and they can induce antiphospholipid syndrome. The presence of aCL has also been reported in streptococcal infection—that is, acute rheumatic fever and infectious endocarditis (IE).6
Here, in 13 patients with PSReA, we determined serum titres of aCL and β2 glycoprotein I (β2GPI) dependent aCL, which is a more crucial antigenic target than cardiolipin itself,7 in order to evaluate the prevalence of aCL and antiphospholipid syndrome. All patients were treated in the outpatient clinic or ward of the Department of Rheumatology, Juntendo Hospital between 1993 and 1998. Patients with PSReA were diagnosed as having an acute sterile arthritis that developed after or during tonsillitis. All patients with PSReA had high titres of antistreptokinase and antistreptolysin O, and group A Streptococcus was isolated from a tonsillar swab in 7/13 patients. Four of the patients underwent tonsillectomy. The patients were followed up in the outpatient clinic for a minimum of three years (mean (SD) 5.2 (2.0) years). The titres of aCL (IgG class) and β2GPI dependent aCL in the sera were determined by an enzyme linked immunosorbent assay (ELISA). Serum samples from 15 healthy subjects and seven patients with IE were also evaluated.
Raised titres of aCL were found in 8/13 patients with PSReA (mean (SD) 2.36 (1.59), cut off index is 1.0), and 6/7 patients with IE (2.07 (1.65)) (fig 1). However, β2GPI dependent aCL were not detected in all patients with PSReA and IE (data not shown). In all the four patients with PSReA who underwent tonsillectomy, raised aCL titres normalised within six months. The raised titres of the remaining four patients with PSReA also fell within two years. No sign of thrombosis was seen in any of the patients with raised aCL titres during the observation period.
The major lipid bacterial component is the phospholipids, moreover, cardiolipin is especially rich in Gram positive bacteria.8 A previous study has shown that the reactivity of IgG class antibody in sera from patients with systemic lupus erythematosus to cardiolipin is inhibited by other phospholipids, such as phosphatidylserine. However, this polyreactivity was not recognised in serum samples from patients with infectious diseases.9 In patients with PSReA, continuous survival of the bacteria, probably in a tonsillar microabscess, may result in transient production of aCL against bacterial cardiolipin. However, our observation suggests that aCL in PSReA are unlikely to lead to thrombotic events.
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