Synovium, rheumatoid synovial joints

In 1943 E. A. Balazs and L. Filler published a paper in which they described a study of role of hyaluronan in dog knee joints. They found that the intercellular substance of connective tissue of the synovium contains sufficient viscous mucin that can replace the mucin removed from the knee [5]. These observations literally opened the door to further studies on the role of hyaluronan in normal and traumatic joints. In 1949, C. Ragan and K. Mayer published a very important paper in which they described the observation of hyaluronan in rheumatoid synovial fluid. This was the first study in which normal and pathological synovial fluids were compared by determination of the concentration and viscosity of hyaluronan [6]. 

Rheumatoid arthritis is a systemic autoimmune disorder produced by an inflammatory response of the synovium of the joints and is accompanied by hyperplasia of synovial cells, excess of synovial fluid, and apparition of fibrous tissue in the synovium, leading together to the destruction of the articular cartilage and ankylosis or fusion of the joints. In a pilot study published... 

Articulated joints between bones, for example at the knee, are covered in a capsule enclosing a space, which contains synovial fluid. The lining of the capsule is composed by the synovial membrane it is this synovium that becomes inflamed in rheumatoid arthritis (RA). Secretions produced by inflammatory cells (lymphocytes, macrophages... 

Rheumatoid arthritis (RA) is an inflammatory disease of the synovium which results in erosion, deformity and finally the destruction of joints. Inflammation of the joints is associated with a villous hypertrophy of the synovial membrane, which on microscopy shows proliferation of the lining layer with an inflammatory infiltrate. There is extensive expression of HLA-... 

In rheumatoid arthritis, immune complexes are deposited in the affected joints, causing an inflammatory response that is amplified by eicosanoids. Lymphocytes and macrophages accumulate in the synovium, whereas leukocytes localize mainly in the synovial fluid. The major eicosanoids produced by leukocytes are leukotrienes, which facilitate T-cell proliferation and act as chemoattractants. Human macrophages synthesize the COX products PGE2 and TXA2 and large amounts of leukotrienes. 

IL-18 augments T- and NK-cell maturation, cytotoxicity and cytokine production. It stimulates TH differentiation, promotes secretion of TNF-a, IFN-y and GM-CSF and enhances NK cell cytotoxicity by increasing FasL expression. IL-8-mediated neutrophil chemotaxis is promoted by IL-18 via its effects on TNF-a and IFN-y, which are stimulatory in action. It plays an important role in maintaining synovial inflammation and inducing joint destruction in rheumatoid arthritis. In synovium of patients with rheumatoid arthritis, enhanced levels of TNF-a and IL-1 are associated with augmented expression of IL-18. 

Chronic inflammation of the synovial tissue lining the joint capsule results in the proliferation of this tissue. The inflamed, proliferating synovium characteristic of rheumatoid arthritis is called parmus (Fig. 89-1). This pannus invades the cartilage and eventually the bone surface, producing erosions of bone and cartilage and leading to destruction of the joint. The factors that initiate the inflammatory process are unknown. 

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