Rheumatoid factor (RF) is the autoantibody (antibody directed against an organism's own tissues) that is most relevant in rheumatoid arthritis. It is defined as an antibody against the Fc portion of IgG. RF and IgG join to form immune complexes that contribute to the disease process.
Rheumatoid factor can also be a cryoglobulin (antibody that precipitates on cooling of a blood sample); it can be either type 2 (monoclonal IgM to polyclonal IgG) or type 3 (polyclonal IgM to polyclonal IgG) cryoglobulin.
Rheumatoid factor can be of either isotype of immunoglobulins, i.e. IgA, IgG, IgM, IgE, IgD.
Read more about Rheumatoid Factor: Testing, Interpretation, History
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