Rheumatoid factors are immunoglobulins with specificity for allotypic determinants located on the

Rheumatoid factors are immunoglobulins with specificity for allotypic determinants located on the

• A. Fc fragment of IgG
• B. Fab fragment of IgG
• C. J chain of IgM
• D. Secretory component of IgA

Answer: (A)

Rheumatoid factors are antibodies that specifically bind the Fc portion of IgG, recognizing allotypic determinants in that constant region. This Fc-targeting pattern is what defines RF activity, leading to immune complex formation that can contribute to joint inflammation. The Fab region is the antigen-binding part of IgG and is not what RF recognizes. The J chain is involved in polymerization of IgM and IgA, not in RF targeting. The secretory component is part of secretory IgA in mucosal immunity, again not related to RF. So the Fc fragment of IgG is the correct target.

Rheumatoid factors are antibodies that specifically bind the Fc portion of IgG, recognizing allotypic determinants in that constant region. This Fc-targeting pattern is what defines RF activity, leading to immune complex formation that can contribute to joint inflammation. The Fab region is the antigen-binding part of IgG and is not what RF recognizes. The J chain is involved in polymerization of IgM and IgA, not in RF targeting. The secretory component is part of secretory IgA in mucosal immunity, again not related to RF. So the Fc fragment of IgG is the correct target.