Basic and Clinical Sciences (BCSE) Practice Exam

Which immunoglobulin classes are primarily involved in type III hypersensitivity reactions?

1. IgA and IgD

2. IgG and IgM

3. IgE and IgM

4. IgG and IgA

The correct answer is: IgG and IgM

Type III hypersensitivity reactions, also known as immune complex-mediated reactions, primarily involve the immunoglobulin classes IgG and IgM. In this type of hypersensitivity, antigen-antibody complexes are formed when these immunoglobulins bind to soluble antigens. Once these complexes are formed, they may deposit in various tissues, leading to an inflammatory response as the immune system attempts to eliminate them. This can result in tissue damage due to the activation of complement and the recruitment of inflammatory cells, causing conditions such as serum sickness, certain types of vasculitis, and glomerulonephritis. The other immunoglobulin classes, such as IgA, IgD, and IgE, do play roles in different immune responses. For instance, IgE is primarily involved in allergic reactions and responses to parasitic infections, while IgA is crucial for mucosal immunity. However, they do not play a significant role in the mechanism of type III hypersensitivity, which is why IgG and IgM are the correct answers in this context.