**Core Concept**
Exotoxins are a type of bacterial toxin produced by certain bacteria, particularly gram-positive bacteria like Clostridium tetani and Corynebacterium diphtheriae. These toxins are secreted outside the bacterial cell and can cause a range of systemic effects, often leading to severe disease.

**Why the Correct Answer is Right**
Exotoxins are highly potent and can act on various cellular targets, leading to their pathogenic effects. For example, tetanus toxin (exotoxin) acts by inhibiting the release of neurotransmitters, causing muscle rigidity and spasms. Diphtheria toxin also acts by inhibiting protein synthesis in host cells, leading to cell death and tissue damage.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because exotoxins are indeed highly specific and can target specific cellular receptors or enzymes, leading to their toxic effects.
**Option B:** This option is incorrect because exotoxins are not produced by all bacteria, but rather by specific strains like those mentioned above.
**Option C:** This option is incorrect because exotoxins can indeed be neutralized by antitoxins, which are antibodies that specifically bind to the toxin and prevent it from causing harm.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that exotoxins can be neutralized by antitoxins, which are often used as post-exposure prophylaxis or treatment for diseases caused by these toxins.

**Correct Answer:** B. Exotoxins are produced by gram-negative bacteria.