This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
[{'content': 'Antibody in cold agglutin disease is \nSelect and explain. \nA. IgA, B. IgG, C. IgE, D. IgM', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Cold agglutinin disease (CAD): This designation is used for a form of chronic AIHA that usually affects the elderly. First, the term cold refers to the fact that the autoantibody involved reacts with red cells poorly or not at all at 37degC, whereas it reacts strongly at lower temperatures. As a result, hemolysis is more prominent the more the body is exposed to the cold. The antibody is usually IgM; usually, it has an anti-I specificity (the I antigen is present on the red cells of almost everybody)Harrison 19e pg: 659', 'role': 'assistant'}]