Does type III hypersensitivity occur with antigen or antibody excess?

Type III hypersensitivity is characterized by the formation of immune complexes, which consist of antigens bound to antibodies. This form of hypersensitivity reaction typically occurs when there is an excess of antigen relative to antibodies. In this scenario, the abundance of antigen leads to the formation of large immune complexes, which can precipitate out of circulation.

These immune complexes can accumulate in tissues and circulate in the bloodstream, leading to localized inflammation and tissue damage as they activate the complement system and attract inflammatory cells. The process is central to conditions such as serum sickness and certain autoimmune diseases, where the body generates an immune response against excess antigens rather than in response to a balanced or antibody-dominant situation.

In contrast, antibody excess would typically lead to a different type of immune response, where free antibodies may neutralize pathogens effectively without forming harmful complexes. Therefore, the correct choice identifies that type III hypersensitivity primarily occurs in the presence of antigen excess.