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© Dirk Biddle
Rheumatoid factor (RF) in serum is primarily immunoglobulin M (less often IgG, IgA, or IgE) directed against the Fc portion of IgG. Normally antibodies help destroy invading bacteria and viruses that can cause disease, however RF is an antibody that can attach to normal tissue, resulting in damage, the exact mechanism of which is unknown. Nevertheless, the presence of RF leads to the formation of immune complexes which activate the classical complement cascade and thus the formation of the strongly chemotactic factors C3a and C5a. These factors, as we have seen, can attract leucocytes into the blood vessel walls, resulting in reactive inflammation and damage.
Rheumatoid factor is present in 80% of cases of rheumatoid arthritis (where it is involved in a cell-mediated type IV immunity process) and in many other autoimmune conditions where high levels of RF are associated with systemic complications such as vasculitis, neuropathy and nodules. In rheumatoid arthritis, the antibody may be synthesised locally within the joints (where it is primarily IgG). RF is also found in many normal members of the population, its incidence increasing with age in the absence of any pathology.
Rheumatoid factor is not usually associated with primary vasculitides, but is noted in Cryoglobulinemia (IgG). RF is usually associated with collagen related secondary vasculitis conditions such as Scleroderma, Sjögren's Syndrome, and Systemic Lupus erythematosus.
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Fc-Receptor: Receptors present on a variety of cells for the Fc fragment of immunoglobulins. These receptors recognise immunoglobulins of the IgG and IgE class.
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Testing information: http://www.aruplab.com/guides/clt/tests/clt_186b.jsp#1147119