Final answer:
Each of the five classes of antibodies—Immunoglobulins IgM, IgG, IgA, IgE, and IgD—has a particular structure and a specific role in the body's immune response, such as initial defense, mucosal immunity, cross-placenta protection, triggering allergic reactions, and immune activation.
Step-by-step explanation:
There are five major classes of antibodies, also known as immunoglobulins, each with a unique structure and role in the immune system. The IgM class is typically the first to respond to infection and is structured as a pentamer, allowing it to bind multiple antigens effectively. IgG antibodies are monomers that are abundant in the serum and can cross the placenta, providing immunity to the fetus.
IgA antibodies can be found as monomers or dimers and are primarily involved in mucosal immunity. IgE, associated with allergic reactions, is a monomer that binds to allergens and triggers histamine release from mast cells and basophils. Lastly, IgD, which exists as a monomer on B cells, plays a role in initiating immune responses. Each antibody class is essential for the body to recognize and neutralize pathogens effectively.