A Young Couple Brings Their 3-Month Old Baby to the Emergency

A young couple brings their 3-month old baby to the emergency department where you work as a triage nurse. The parents tell you that the baby had a runny nose, low grade fever, and mild cough two days earlier, which they assumed was a cold. However, the cough has become significantly worse and they are really worried about the gasping sound the child makes when breathing in after a coughing spell. The baby's cough is so bad that she has been vomiting and is refusing to feed. You are concerned that the baby has pertussis, commonly known as whooping cough. You give the parents some information while they are waiting for a physician to examine their child.
-You are very concerned about your patient because you know that B. pertussis releases three toxins that play a role in disease progression. One of these, pertussis toxin (PT) is an A-B toxin that causes an increase in mucus production by cells in the respiratory tract. The parents ask you to explain what you mean by an A-B toxin. Which of the following would you NOT tell them?

A) Exotoxins are proteins, so the immune system can generally produce neutralizing antibodies against them.
B) A-B toxins consist of two parts: the A subunit is the toxic (active) portion and the B subunit binds to a specific surface molecule on cells.
C) A-B toxins are exotoxins that are produced by Gram-positive cells but not by Gram-negative cells.
D) Epithelial cells of the respiratory system possess receptors to which the B portion of PT can bind.
E) A vaccine that protects against toxin-mediated disease are call toxoids; these vaccines contain inactivated toxins.