Which antibodies are known to react with complement?

The correct answer is based on the understanding of how different antibody classes interact with the complement system, which is an essential part of the immune response.

IgM and IgG are the antibody types most recognized for their ability to activate the complement pathway. IgM is particularly effective because it forms a pentameric structure capable of binding multiple antigen molecules, which leads to efficient complement activation via the classical pathway. This complement activation generates various immune responses, including opsonization of pathogens and promotion of inflammation.

IgG also plays a significant role in activating the complement. While there are several subclasses of IgG, the most known for this activity are IgG1 and IgG3, capable of forming complexes with antigens that trigger complement activation.

In contrast, other antibody classes such as IgA and IgE, while they have essential roles in the immune response, do not significantly activate complement compared to IgM and IgG. IgD is primarily involved in B cell receptor functions and does not engage effectively with complement either.

Thus, the interaction of IgM and IgG antibodies with complement underscores their importance within the adaptive immune system, highlighting why they are the correct answer in this context.