- Serum Sickness is the prototype example of Type III Hypersensitivity and is caused by formation of immune complexes with exogenously delivered proteins in horse plasma.
- Historically, treatment for exposure to certain toxins was achieved by injection of plasma derived from horses which had been immunized by the toxin. Injection of horse plasma provided the patient with passive immunity to the toxin by transferring toxin-specific horse antibodies to the patient. Unfortunately, most humans mount a humoral immune response to equine plasma proteins and thus generate anti-horse antibodies. These anti-horse antibodies bind horse plasma proteins resulting in the generation of immune complexes that deposit in a number of tissues and induce a prototypical Type III Hypersensitivity reaction. Because of the serious clinical consequences, passive immunization with horse plasma is no longer performed and thus serum sickness is now very rare.
- Urticaria: Complex deposition in skin
- Arthralgia: Complex deposition in joints
- Nephritic Syndrome: Complex deposition in the glomerulus
- Fever and lymphadenopathy: General systemic immune activation