Final answer:
Type III hypersensitivity is an immune complex-mediated hypersensitivity involving the formation of immune complexes that cause inflammation in various tissues. Antibody excess, particularly IgG, is a key factor in this reaction, leading to immune complex deposition and inflammatory damage to organs.
Step-by-step explanation:
Type III hypersensitivity is an immune complex-mediated hypersensitivity, which means the correct answer is B) Immune complex-mediated hypersensitivity. This type of reaction is characterized by the formation of immune complexes (antigen-antibody complexes) that deposit in tissues, triggering an inflammatory response. A unique aspect of Type III hypersensitivity is the presence of antibody excess, typically IgG, with a relatively low concentration of antigen leading to small immune complexes that settle on vascular and tissue surfaces. These immune complexes induce a series of inflammatory events including complement activation, stimulating an inflammatory response, and recruitment and activation of neutrophils, which can result in damage to various organs such as blood vessels, heart tissue, joints, skin, and kidneys.
An example of this response is serum sickness, a systemic type III hypersensitivity condition, which can occur when immune complexes deposit in various parts of the body causing a widespread inflammatory response. If the kidneys are affected by a type III hypersensitivity reaction, it may even require dialysis treatment. The Arthus reaction is a localized form of type III hypersensitivity that transpires when soluble antigens combine with IgG, forming immune complexes in the skin.