Final answer:
IgM, because of its pentameric shape and ten antigen-binding sites, is the most potent activator of the complement system compared to other immunoglobulin isotypes like IgG1 or IgG4. The option (E) is correct.
Step-by-step explanation:
The immunoglobulin isotype that is the strongest activator of the complement system is IgM. IgM is the first antibody produced during a primary immune response, and because of its pentameric structure, it is very effective at activating the complement system. IgM consists of five monomers bound together, with ten antigen-binding sites, allowing for a robust binding to pathogens and subsequent activation of the complement pathway.
In contrast, IgG antibodies, including subclasses such as IgG1 and IgG4, are monomers and do not activate complement as effectively as IgM. However, IgG is significant as it is involved in secondary immune responses and is the most abundant antibody in the serum, important for pathogen clearance and maternal-fetal protection. Therefore, option (E) is correct.
This question is not complete, Here I am attaching the complete question:
Which of the following immunoglobulin isotypes is the strongest activator of the complement system?
(A) IgD
(B) IgE
(C) IgG1
(D) IgG4
(E) IgM