Aim. Investigation of associations of reactive arthritis (ReA) with hi
stocompatibility antigens class I and II and determination of new appr
oaches to assessment of association ReA with antigen HLA B27. Material
s and methods. 118 ReA patients,vith associated intestinal and 82 ReA
patients with associated urogenital infection were studied The infecti
on was identified bacteriologically, with agglutination reaction, enzy
me immunoassay, direct and indirect immunofluorescence, culturing. HLA
-antigens were studied in lymphocytotoxic test: locus A. B and C in al
l the patients, DR in 65 patients. Results. ReA triggers were intracel
lularly parasite bacteria: facultative parasites in the enterocolitic
variant (Yersinia, as a rule), obligate parasite in the urogenital (Ch
lamidia, as a rule). HLA B27 antigen runs discovered in 77.5% of patie
nts (RR 45.8), HLA DR1 - in 48.4% of patients (RR 3.3). in urogenital
variant HLA B27 antigen occurred more frequently than in enterocolitic
: 87.8% (RR 95.6) versus 70.3% (RR 31.5); p < 0.01). In HLA-B27-positi
ve patients compared to HLA-B27-negative ones there were higher ESR (p
< 0.001), leukocyte count (p < 0.05), concentrations of CRP and alpha
-2-globulins (p < 0.001). Conclusion, In HLA-B27-subjects optimal cond
itions exist for generalization of obligate parasites and favorable fo
r production of facultative ones. The degree of association of ReA wit
h HLA B27 antigens is dependent on adaptive features of microorganisms
appearing in the process of evolution - obligaty and facultativeness
of their internal parasitivity.