What characterizes type III hypersensitivity reactions?

Type III hypersensitivity reactions are characterized by the formation of immune complexes, which are aggregates of antigens and antibodies. These immune complexes can deposit in various tissues and lead to inflammation and damage through the activation of the complement system and recruitment of inflammatory cells.

In type III reactions, the immune response occurs when there is an excess of antigen, leading to the formation of stable immune complexes. These complexes can deposit in the kidneys, skin, and joints, causing conditions such as systemic lupus erythematosus or rheumatoid arthritis. The pathophysiology includes damage mediated by complement activation and the subsequent recruitment of neutrophils, which release inflammatory mediators that contribute to tissue damage.

While other types of hypersensitivity reactions may involve immediate responses or T cells, type III specifically revolves around the concept of immune complexes and their effects on tissue inflammation and damage. This distinct feature is what defines type III hypersensitivity and differentiates it from others.