Final answer:
IgM is the first secreted antibody during the immune response, while IgE is present in negligible amounts in the serum and is known for its role in mediating allergic responses.
Step-by-step explanation:
IgM is the first antibody to be produced and secreted during the immune response. In the blood plasma, IgM molecules are assembled into larger structures called pentamers, linked by a J chain, allowing them to bind multiple antigens. Another antibody, IgD, is present on the surface of naive B cells and is found in negligible amounts in the serum, mostly originating from the degradation of old B cells. Unlike IgM, IgD does not play a significant role in the secreted antibody response.
There are other immunoglobulin classes, such as IgG, IgA, and IgE. IgG is the main blood antibody of late primary and early secondary responses, while IgA is essential for mucosal immunity. IgE, present in the least amount in the serum, is critical for anti-parasitic defenses and allergy mediation. Given the context of the question, the correct answer is d) IgE, which is present but in negligible amounts in the bloodstream.