Final answer:
Antibodies bind to antigens in the immune system and trigger defense reactions. Type II hypersensitivity reactions involve cellular antigens and result in cell damage, while type III hypersensitivity reactions involve immune complex formation and tissue damage.
Step-by-step explanation:
In the immune system, antibodies (also known as immunoglobulins) play a crucial role in defending the body against pathogens. They bind to specific antigens (foreign substances) and trigger various defense reactions. There are five classes of antibodies, each with its own mechanism of action. Antibodies can neutralize pathogens, mark them for phagocytosis, or activate the complement cascade.
Type II hypersensitivity reactions involve the binding of IgG and IgM antibodies to cellular antigens, resulting in cell damage. This damage is carried out by other components of the immune system. Type III hypersensitivity reactions occur when immune complexes form between antibodies and antigens, leading to tissue damage.
In summary, antibodies bind to antigens and initiate specific defense reactions in the immune system. Type II hypersensitivity reactions involve antibodies directed against cellular antigens, causing cell damage, while type III hypersensitivity reactions involve the formation of immune complexes that damage tissues.