Hypersensitivity and Autoimmunity · USMLE Step 1

A patient with rheumatoid arthritis has circulating rheumatoid factor. What does this factor bind?

  1. IgG Fc portion
  2. IgM heavy chain
  3. Complement C5a
  4. IL-1 receptor
Show answer and explanation

Correct answer: IgG Fc portion

Rheumatoid factor is an IgM antibody targeting the Fc portion of IgG. It contributes to immune complex formation.

Difficulty: Medium Question 14 of 20

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