What type of antibodies are indicative of immune complex diseases?

Immune complex diseases are characterized by the presence of immune complexes, which are formed when antibodies bind to antigens. IgG antibodies play a significant role in the formation of these immune complexes. When the body is exposed to an antigen, IgG antibodies are produced as part of the adaptive immune response. These complexes can deposit in various tissues throughout the body, leading to inflammation and tissue damage, which are hallmarks of immune complex diseases such as systemic lupus erythematosus, rheumatoid arthritis, and certain types of glomerulonephritis.

While other immunoglobulin classes have their roles in immune responses, they do not primarily indicate immune complex diseases to the same extent that IgG does. IgA is predominantly found in mucosal areas and provides localized immune protection. IgM is the first antibody produced during an initial exposure to an antigen but is less often associated with chronic immune complex diseases. IgE is primarily involved in allergic reactions and responses to parasitic infections rather than forming immune complexes.

Thus, the presence of IgG antibodies is a key indicator of immune complex diseases, making it the correct answer.