Detection ofMycobacterium tuberculosisGroup Organisms in Human and Mouse Joint Tissue by Reverse Transcriptase PCR: Prevalence in Diseased Synovial Tissue Suggests Lack of Specific Association with Rheumatoid Arthritis

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Abstract
Infection with mycobacterial species, includingMycobacterium tuberculosis, has long been implicated in the etiopathology of rheumatoid arthritis (RA) on the basis of clinical and pathological similarities between tuberculosis and RA. Despite evidence of immune responses to mycobacterial antigens in RA patient synovial fluid, cross-reactivity between these and host joint antigens, and the presence ofM. tuberculosisprotein antigen in RA synovial fluid, a definite causal association with RA has not been shown. Previous studies from our laboratory using reverse transcriptase PCR (RT-PCR) of bacterial rRNAs have shown RA synovium to be colonized by a diverse range of bacteria, most of commensal origin. However,M. tuberculosisgroup organism (MTG) RNA sequences were found in one RA patient tissue. Since this was considered of sufficient interest to warrant further investigation, we devised aM. tuberculosis-specific nested RT-PCR test which could be used for detection of MTG in a mixed pool of bacterial crDNAs. This test was used to investigate the distribution of MTG in RA synovial tissue and also non-RA arthritis and healthy control tissues and was also used to examine the tissue distribution of MTG in an acute and chronic model ofM. tuberculosisinfection in the BALB/c mouse. MTG sequences were found in a high proportion of RA patient synovial tissues but also in non-RA arthritis control tissues at lower frequency. This likely reflects trafficking of persistentM. bovisBCG to inflamed joint tissue, irrespective of cause. MTG were not found in healthy synovial tissue or the tissue of patients with undifferentiated arthritis. In both the acute and chronic models of infection in BALB/c mice,M. tuberculosiswas also found to have trafficked to joint tissues, however, no signs of inflammation, arthritis, or pathology associated withM. tuberculosisinfection was seen. These combined results would argue against a specific causal role of MTG in RA-like arthritis; however, their role as adjuvant in immune dysfunction in an innately susceptible host cannot be excluded.