Editing Rheumatoid factor (section)

{{Short description|Autoantibody found in rheumatoid arthritis}}
{{Distinguish|Rhesus factor}}

'''Rheumatoid factor''' ('''RF''') is the [[autoantibody]] that was first found in [[rheumatoid arthritis]]. It is defined as an [[antibody]] against the [[Fragment crystallizable region|Fc]] portion of [[IgG]] and different RFs can recognize different parts of the IgG-Fc.<ref>{{cite journal|last1=Falkenburg|first1=W.J.J.|title=IgG Subclass Specificity Discriminates Restricted IgM Rheumatoid Factor Responses From More Mature Anti–Citrullinated Protein Antibody–Associated or Isotype-Switched IgA Responses|journal=Arthritis & Rheumatology|date=November 2015|volume=67|issue=12|pages=3124–3134|doi=10.1002/art.39299|pmid=26246004|ref=IgG Subclass Specificity Discriminates Restricted IgM Rheumatoid Factor Responses From More Mature Anti–Citrullinated Protein Antibody–Associated or Isotype-Switched IgA Responses|doi-access=free}}</ref> RF and IgG join to form [[immune complex]]es that contribute to the [[disease]] process such as chronic inflammation and joint destruction at the [[Synovial membrane|synovium]] and [[cartilage]].<ref>{{cite journal |vauthors=Edkins A, Cushley W | year = 2012 | title = The Jekyll and Hyde nature of antibodies | journal = Biological Sciences Review | volume = 25 | issue = 2| page = 4 }}</ref>

Rheumatoid factor can also be a [[cryoglobulin]] (antibody that precipitates on cooling of a blood sample); it can be either type&nbsp;2 ([[monoclonal]] [[IgM]] to [[polyclonal]] IgG) or type&nbsp;3 (polyclonal IgM to polyclonal IgG) cryoglobulin.

Although ''predominantly'' encountered as IgM, rheumatoid factor can be of any [[isotype (immunology)|isotype]] of [[immunoglobulins]]; i.e., IgA, IgG, IgM,<ref>{{cite journal |pmid=3775335 |year=1986 |last1=Hermann |first1=E |last2=Vogt |first2=P |last3=Müller |first3=W |title=Rheumatoid factors of immunoglobulin classes IgA, IgG and IgM: Methods of determination and clinical value |volume=116 |issue=38 |pages=1290–7 |journal=Schweizerische Medizinische Wochenschrift}}</ref> IgE,<ref>{{cite journal |pmid=1669588 |year=1991 |last1=Herrmann |first1=D |last2=Jäger |first2=L |last3=Hein |first3=G |last4=Henzgen |first4=M |last5=Schlenvoigt |first5=G |title=IgE rheumatoid factor. Occurrence and diagnostic importance in comparison with IgM rheumatoid factor and circulating immune complexes |volume=1 |issue=5 |pages=302–7 |journal=Journal of Investigational Allergology & Clinical Immunology}}</ref> IgD.<ref>{{cite journal |pmid=1418183 |year=1992 |last1=Banchuin |first1=N |last2=Janyapoon |first2=K |last3=Sarntivijai |first3=S |last4=Parivisutt |first4=L |title=Re-evaluation of ELISA and latex agglutination test for rheumatoid factor detection in the diagnosis of rheumatoid arthritis |volume=10 |issue=1 |pages=47–54 |journal=Asian Pacific Journal of Allergy and Immunology}}</ref>