Final answer:
The five classes of human antibodies are IgM, IgD, IgG, IgA, and IgE, each with different heavy chains, structures, locations, and roles in the immune response. IgM is the first produced, IgG is the most abundant, IgA is found in mucosal areas, IgD's function is largely unknown, and IgE is involved in allergic responses and defense against parasites.
Step-by-step explanation:
Five Classes of Antibodies
In the human immune system, there are five distinct classes of antibodies, each with a unique structure and function. These are IgM, IgD, IgG, IgA, and IgE. The constant region of an antibody molecule determines its class. IgM is typically the first antibody produced in response to an antigen and is pentameric, with a larger size allowing for multiple antigen binding sites. IgG antibodies are the most abundant and are known for their role in the body's secondary response to pathogens. IgA antibodies are found in mucosal areas, such as the gut, and are important for localized immunity. IgD functions mainly as a receptor on B cells, and no other significant function has been discovered. Lastly, IgE is associated with allergic reactions and parasitic infections, playing a critical role in mediating immune responses.
The unique heavy chains designated by Greek letters γ, μ, α, δ, and ε correspond to IgG, IgM, IgA, IgD, and IgE antibodies, respectively. These classes differ in terms of their abundance in serum, their structural arrangement, sites of action within the body, and their specialized roles in immunity.