Which of the following is true regarding exotoxins and endotoxins?

• A. Both endotoxin and exotoxins are highly immunogenic allowing for the development of protective antibodies and vaccines.
• B. Endotoxin and exotoxin are both released from live bacteria.
• C. Endotoxin is released from the cell wall of dead bacteria, whereas exotoxin is released from live bacteria.
• D. Endotoxin and exotoxins bind to specific receptors on a bacterial cell leading to cell lysis.

Answer: (C)

Exotoxins and endotoxins differ in what they are and how they’re released. Exotoxins are proteins produced by living bacteria and actively secreted into the surrounding environment, where they can target specific host cells. Because they’re proteins, they tend to be highly immunogenic, and vaccines can be made using detoxified forms of these toxins. Endotoxins are lipopolysaccharide components of the outer membrane of Gram-negative bacteria. They’re not secreted as toxins by living cells; they’re released mainly when the bacteria die or lyse, and they provoke strong inflammatory responses but are relatively poorly immunogenic.

Thus, the statement that endotoxin is released from the cell wall of dead bacteria, whereas exotoxin is released from live bacteria, is the correct description.