Porphyromonas gingivalis and the pathogenesis of rheumatoid arthritis: analysis of various compartments including the synovial tissue

Introduction: We evaluated the presence of Porphyromonas gingivalis (Pg) DNA in the\r\nsynovial tissue through synovial biopsy and in other compartments of RA patients in\r\ncomparison with patients affected by other arthritides. Possible links with clinical,\r\nimmunologic and genetic features were assessed.\r\nMethods: Peripheral blood (PB), sub-gingival dental plaque, synovial fluid (SF) and synovial\r\ntissue samples were collected from 69 patients with active knee arthritis (32 with RA and 37\r\nwith other arthritides, of which 14 with undifferentiated peripheral inflammatory arthritis -\r\nUPIA). Demographic, clinical, laboratory and immunological data were recorded. The\r\npresence of Pg DNA was evaluated through PCR. The HLA-DR haplotype was assessed for\r\n45 patients with RA and UPIA.\r\nResults: No differences arose in the positivity for Pg DNA in the sub-gingival plaque, PB\r\nand SF samples between RA and the cohort of other arthritides. Full PB samples showed a\r\nhigher positivity for Pg DNA than plasma samples (11.8% vs. 1.5%, p=0.04). Patients with\r\nRA showed a higher positivity for Pg DNA in the synovial tissue compared to controls\r\n(33.3% vs. 5.9%, p<0.01). UPIA and RA patients carrying the HLA DRB1*04 allele showed\r\na higher positivity for Pg DNA in the synovial tissue compared to patients negative for the\r\nallele (57.1% vs. 16.7%, p=0.04). RA patients positive for Pg DNA in the sub-gingival\r\nplaque had a lower disease duration and a higher peripheral blood leucocytes and neutrophils\r\ncount. The presence of Pg DNA did not influence disease activity, disease disability or\r\npositivity for autoantibodies.\r\nConclusions: The presence of Pg DNA in the synovial tissue of RA patients suggests a\r\npathogenic role of the bacterium. The higher positivity of Pg DNA in full peripheral blood\r\nand synovial tissue samples compared to plasma and synovial fluid suggests a possible\r\nintracellular localization of Pg, in particular in patients positive for HLA-DR4.