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: Medicine
Rh factor is 
Select and explain. 
A. IgM antibody, B. Mucppolysaccharide, C. IgG antibody, D. Fatty acid
A: IgM antibody
Answer: A: IgM antibody 
Explanation: A i.e. IgM antibody - Rheumatoid (Rh) factor in rheumatoid ahritis is an autoantibody of IgM class directed against Fc fragment of IgGQ. - Antibodies (immunoglobins) are glycoproteins. And Rh factors is an autoantibody of any immunoglobin class directed against Fc fragment of IgG immunoglobin (Davidson).