ACAAI Board Practice Exam 2026 – 400 Free Practice Questions to Pass the Exam

Type II hypersensitivity, also known as cytotoxic hypersensitivity, primarily involves the immunoglobulins IgG and IgM. This form of hypersensitivity occurs when antibodies bind to antigens present on the surface of certain cells, leading to cell damage or destruction. The binding of these antibodies activates the complement system and facilitates opsonization, phagocytosis, or direct lysis of the target cells.

IgG is the most prevalent immunoglobulin in serum and has a high affinity for antigens, making it particularly effective in mediating type II reactions. IgM, although present in lower concentrations than IgG, is very effective as well because it can form a pentamer structure that increases its valency and ability to activate the complement pathway. Both of these immunoglobulins play critical roles in the immune system's response to infections and in the pathogenesis of autoimmune diseases where the host's cells are mistakenly targeted.

As for the other options, IgA and IgE are primarily involved in mucosal immunity and allergic responses, respectively. IgD has a more mysterious role and is not typically associated with hypersensitivity reactions like type II. Thus, the significance of IgG and IgM in mediating cellular damage in type II hypersensitivity