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Rheumatoid factor test
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Rheumatoid factor is an antibody with one odd feature: it is aimed at another antibody. It is a guard whose job is to flag another guard. Specifically, it goes after the Fc portion of IgG, the stem part of the molecule. When people say rheumatoid factor with nothing else added, they almost always mean the IgM type.
What it does is bind those IgG molecules and form immune complexes, clumps of stuck-together antibodies that inflammatory cells then swallow whole, that is, phagocytose. The ones produced in the germinal center are low affinity, transient and polyclonal, meaning they grip loosely, they do not last long, and they come from many different cells.
And here is the catch in the name. Rheumatoid factor is not unique to rheumatoid arthritis: it is found in other diseases, autoimmune and non-autoimmune, and in up to 4% of healthy young people and older adults.
In brief
Rheumatoid factor is an antibody directed against the Fc portion of IgG, and the one most often mentioned is the IgM type.
It forms immune complexes that inflammatory cells phagocytose, and the antibodies produced in the germinal center are low affinity, transient and polyclonal.
It is not unique to rheumatoid arthritis: it shows up in other diseases, autoimmune or not, and in up to 4% of healthy young people and older adults.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingRheumatoid Factor, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated