Which is an example of type-III hypersensitivity
**Core Concept**
Type-III hypersensitivity reactions involve the formation of antigen-antibody complexes (immune complexes) that deposit in tissues, leading to complement activation, inflammation, and tissue damage. This type of reaction is often seen in conditions such as systemic lupus erythematosus (SLE) and serum sickness.
**Why the Correct Answer is Right**
In a type-III hypersensitivity reaction, the interaction between the antigen and the antibody results in the formation of immune complexes. These complexes can bind to complement proteins, leading to the activation of the complement cascade and the release of pro-inflammatory mediators. This process ultimately results in tissue damage and inflammation. The classic example of a type-III hypersensitivity reaction is the Arthus reaction, which occurs when an individual is exposed to an antigen to which they have pre-existing antibodies.
**Why Each Wrong Option is Incorrect**
**Option A:** This option refers to a type-I hypersensitivity reaction, which involves the release of histamine and other mediators from mast cells, leading to allergic symptoms such as hives and anaphylaxis.
**Option B:** This option refers to a type-II hypersensitivity reaction, which involves the binding of antibodies to cell surface antigens, leading to cell destruction through mechanisms such as complement activation or antibody-dependent cellular cytotoxicity.
**Option C:** This option refers to a type-IV hypersensitivity reaction, which involves the activation of T lymphocytes, leading to cell-mediated immunity and the release of pro-inflammatory cytokines.
**Clinical Pearl / High-Yield Fact**
The Arthus reaction is a classic example of a type-III hypersensitivity reaction and is often seen in individuals who have been exposed to an antigen to which they have pre-existing antibodies. This reaction can be prevented by administering corticosteroids or other immunosuppressive agents.
**Correct Answer: D.**