Which of the following is a superantigen ?
**Core Concept**
A superantigen is a type of microbial toxin or immune molecule that can cause excessive activation of the immune system, leading to a strong inflammatory response. This is in contrast to traditional antigens, which stimulate a more targeted and regulated immune response.
**Why the Correct Answer is Right**
Staphylococcal enterotoxin B (SEB) is a potent superantigen produced by Staphylococcus aureus. It works by binding to the major histocompatibility complex (MHC) class II on antigen-presenting cells and the T-cell receptor (TCR) on T-cells, causing a massive release of cytokines and activation of a large number of immune cells. This leads to a strong inflammatory response, which can cause symptoms such as fever, rash, and even shock.
**Why Each Wrong Option is Incorrect**
* **Option A:** Tetanus toxin is a neurotoxin produced by Clostridium tetani, which causes muscle stiffness and spasms by blocking neurotransmitter release at the neuromuscular junction. It is not a superantigen.
* **Option B:** Diphtheria toxin is a protein produced by Corynebacterium diphtheriae, which causes tissue damage by inhibiting protein synthesis in host cells. It is not a superantigen.
* **Option C:** Lipopolysaccharide (LPS) is a component of the outer membrane of Gram-negative bacteria, which stimulates an immune response by binding to Toll-like receptor 4 (TLR4) on immune cells. While LPS can cause a strong inflammatory response, it is not considered a superantigen.
**Clinical Pearl / High-Yield Fact**
Superantigens like SEB can cause a condition known as toxic shock syndrome (TSS), characterized by fever, rash, and multi-organ failure. TSS is a medical emergency that requires prompt treatment with antibiotics and supportive care.
**Correct Answer: C. Staphylococcal enterotoxin B**