IgG antibodies to LPS of P. gingivalis and the presence of P. gingivalis;laboratory variables: ESR, CRP, RF, ACPA and pro-inflammatory cytokines;clinical RA assessment: TJC, SJC, DAS28,HAQ, radiological evaluation;typing of HLA-DRB1 shared epitope. The gene discussed is HLA-DRB1; the disease is rheumatoid arthritis.