What type of hypersensitivity is associated with serum sickness?

Serum sickness is a classic example of a Type III hypersensitivity reaction. This type of reaction occurs when antigen-antibody complexes are formed in response to an antigen and then get deposited in various tissues, leading to inflammation and tissue damage. In serum sickness, the antibodies are typically formed against foreign proteins, such as those from equine serum used in certain treatments or vaccines.

This process involves the immune system producing IgG or IgM antibodies that bind to circulating antigens. These immune complexes can deposit in tissues such as the kidneys, joints, and skin, causing symptoms like fever, rash, arthralgias, and sometimes more severe effects such as glomerulonephritis. The hallmark of Type III hypersensitivity is the formation of these immune complexes, which is distinct from the mechanisms involved in Type I (immediate hypersensitivity), Type II (antibody-mediated cytotoxicity), and Type IV (delayed-type hypersensitivity) reactions. Each of these other types of hypersensitivity reactions involves different immune pathways and cellular responses that do not primarily involve the deposition of immune complexes as seen in serum sickness.