What class of antibody includes anti-A and anti-B antibodies?

What class of antibody includes anti-A and anti-B antibodies?

• A. IgE
• B. IgA
• C. IgM
• D. IgD

Answer: (C)

The class of antibody that includes anti-A and anti-B antibodies is IgM. These antibodies are part of the innate immune response and are typically the first antibodies produced in response to an antigen. In the context of blood types, anti-A and anti-B antibodies play a crucial role in the ABO blood group system. Their presence in the bloodstream can lead to agglutination of red blood cells if mismatched blood is transfused, as they target the A and B antigens on the surface of red blood cells.

IgM is characterized by its pentameric structure, which allows for a high avidity for binding to multiple antigens simultaneously, making it very effective in initiating immune responses. In contrast, the other classes of antibodies, such as IgE (involved in allergy responses), IgA (found in mucosal areas), and IgD (primarily a receptor on B cells), do not contain the specificities for A and B antigens that are necessary for the agglutination reactions associated with blood types.