This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pathology
Rheumatoid factor is directed against ? 
Select and explain. 
A. IgG, B. IgD, C. 1gM, D. IgA
A: IgG
Answer: A: IgG 
Explanation: Ans. is 'a' i.e., IgG Rheumatoid factor in Rheumatoid Ahritis is an IgM antibody directed against the Fc fragment of IgG. Rheumatoid factor in Rheumatoid Ahritis is an IgM antibody directed against the Fe fragment of IgG. Anti CCP antibodies are most specific blood test for rheumatoid ahritis (specificity - 95%). Rheumatoid factor is positive in only 10% of patients with JRA.