The first preparations used for artificially acquired passive immunity were antibodies produced in horse serum. A complication that resulted from the therapeutic use of horse serum was immune complex?

The use of horse serum for artificially acquired passive immunity often led to the formation of immune complexes, which can occur when antibodies bind to antigens, forming aggregates that may trigger inflammatory responses. This can result in adverse reactions, such as serum sickness, characterized by symptoms like fever, rash, and joint pain. Additionally, the introduction of foreign proteins from the horse serum can provoke an immune response in the recipient, complicating treatment outcomes. As a result, while effective, the use of horse serum raised concerns about safety and tolerability in patients.