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: Microbiology
[{'content': 'Which of the following is TRUE about rheumatoid factor? \nSelect and explain. \nA. An albumin, B. 17S globulin, C. 7S globulin, D. 19S globulin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Rheumatoid factors (RFs) are autoantibodies, predominantly IgM isotype (19s IgM), that are directed against multispecies antigenic determinants on the heavy chain of IgG. RFs can arise as an epiphenomenon during acute illness or chronic antigenic stimulation of almost any cause. They are present, in significant titer, in bacterial endocarditis, granulomatous diseases, and most rheumatic diseases. Ref: Textbook of Microbiology By Ananthanarayan And Paniker, 2005, Page 174.', 'role': 'assistant'}]