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Synovial pathology 

Synovial pathology
Synovial pathology
Oxford Textbook of Rheumatology (4 ed.)

Costantino Pitzalis

, Frances Humby

, and Michael P. Seed

Previous versions of this chapter are available. To view earlier versions of this chapter view the full site here.

Synovial pathology is seen in a variety of disease states, including rheumatoid arthritis (RA), osteoarthritis (OA), psoriatic arthritis, and systemic lupus erythmatosus (SLE). This chapter highlights recent advances that characterize the cellular composition of these tissues according to surface markers and chemokine and cytokine expression, and describes synovial functional status and response to therapeutics. In RA, after initiation, pannus migrates over and under cartilage, and into subchondral bone, in a destructive process. Cartilage-pannus junction (CPJ) is characterized as invasive or ’quiescent’ or ’indistinct’. Invasive CPJ can comprise macrophages, fibroblast-like synoviocytes (FLS), mast cells, and/or neutrophils. CPJ activity is related to the state of activation of the overlying subintima. Subintimal inflammation can be graded to a variety of degrees (I–IV) according to established criteria and is illustrated. In some RA synovia, cellular aggregates organize into ectopic lymphoid structures (ELS) through the expression of lymphorganogenic signals, to exhibit T- or B-cell zones accompanied by dendritic cells and lymphangiogenesis. ELS synthesize rheumatoid factor (RF) and anti-citrullinated peptide antibodies (ACAP), considered to be indicative of aggressive disease. The selective cellular expression of macrophage and dendritic cell chemokines and cytokines such as TNF, GMCSF, TGFβ‎, IL-1, IL-6, IL-23, and chemokines can be seen in synovia, to form a regulated and cooperative environment that sustains the cellular organization and pathological function. Important to this process are FLS and CD68+ macrophages. CD68 expression correlates with disease severity and can be useful as a surrogate marker of disease modifying activity of therapeutics, such as anti-TNF and anti-B-cell biologics.

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