**Core Concept**
Superantigens are a class of antigens that cause excessive activation of the immune system, leading to a massive release of cytokines and a severe inflammatory response. This is often seen in conditions such as toxic shock syndrome and severe food poisoning. Superantigens can bind to both the major histocompatibility complex (MHC) class II molecules on antigen-presenting cells and the T-cell receptor (TCR) on T-cells, bypassing the normal antigen presentation pathway.

**Why the Correct Answer is Right**
The correct answer is **Staphylococcal enterotoxin B (SEB)**. SEB is a well-known superantigen produced by Staphylococcus aureus, responsible for causing toxic shock syndrome and food poisoning. It works by binding to the MHC class II molecules on antigen-presenting cells and the TCR on T-cells, leading to a massive activation of T-cells and a subsequent release of cytokines.

**Why Each Wrong Option is Incorrect**
* **Option A:** Staphylococcal enterotoxin A (SEA) is a superantigen, similar to SEB, and is also produced by Staphylococcus aureus.
* **Option B:** Streptococcal pyrogenic exotoxin (SPE) is a superantigen produced by Streptococcus pyogenes, responsible for causing scarlet fever and toxic shock syndrome.
* **Option C:** Tetanus toxin is a neurotoxin produced by Clostridium tetani, which causes tetanus by blocking neurotransmitter release at the neuromuscular junction, but it is not a superantigen.

**Clinical Pearl / High-Yield Fact**
Superantigens can cause a severe inflammatory response by bypassing the normal antigen presentation pathway, leading to a massive release of cytokines and a potentially life-threatening condition.

**Correct Answer: D. Tetanus toxin. Tetanus toxin is a neurotoxin, not a superantigen.**