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Synovial Tissue Analysis in Clinical Studies

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Synovial tissue analysis may provide new insights in studies of the clinical course and outcome, response to treatment and disease mechanisms [1]. In a prospective clinical study of acute phase serum amyloid A (A-SAA) (the principle component of amyloid deposition) in early rheumatoid arthritis (RA), strong correlations with disease activity and response to therapy were observed [2]. A-SAA production by the liver is regulated by the pro-inflammatory cytokines IL-1, TNF-α and IL-6 [3]. Little is known about A-SAA production at peripheral sites of inflammation. This study was undertaken to investigate if A-SAA is produced by inflamed synovium in RA and other arthropathies.

Synoviocytes were cultured following arthroscopic biopsy from patients with early arthritis. Total RNA was analysed for A-SAA mRNA using Northern blot analysis and RT-PCR. Immunohistochemistry was performed on frozen tissue sections using a polyclonal rabbit anti-human antibody. Using immunohistochemistry, A-SAA protein was demonstrated in the superficial layer of the synovial intima and in vascular endothelial cells. A-SAA mRNA was not detectable by Northern blot analysis in cultured synoviocytes. The RT-PCR technique, which is 100-1000 times more sensitive, resulted in the detection of constitutive expression of A-SAA. A fragment of 335 bp nucleotides was identified by RT-PCR and was verified by Southern blot analysis. A-SAA mRNA expression was investigated in cultured synoviocytes in response to inflammatory cytokines. Initial data indicates that IL-1, TNF-α and IL-6 are important regulators of A-SAA expression in these cells.

This is the first study to demonstrate A-SAA gene expression in human synovium. Local production of A-SAA, demonstrated by both RT-PCR and immunohistochemistry, suggests a physiological role for A-SAA at sites of inflammation.

References

  1. 1.

    Bresnihan B, Tak PP: Synovial tissue analysis in rheumatoid arthritis. Balliere's Clini Rheumatol. 1999, 13: 85-99.

  2. 2.

    Cunnane G, Grehan S, Geoghegan S, et al: Serum amyloid A in the assessment of early inflammatory arthritis. J Rheumatol . 1999,

  3. 3.

    Steel DM, Whitehead AS: The major acute phase reactants: C-reactive protein, serum amyloid P component and serum amyloid A protein. Immunology Today. 1994, 15: 81-88. 10.1016/0167-5699(94)90138-4.

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Keywords

  • Rheumatoid Arthritis
  • Northern Blot Analysis
  • Arthropathy
  • Early Rheumatoid Arthritis
  • Prospective Clinical Study