[Campbell Biology P.1025] Given that polio is caused by a virus that infects neurons, and the... | Practice Question

Given that polio is caused by a virus that infects neurons, and the body cannot replace most neurons, why is it crucial for a polio vaccine to stimulate both a cell-mediated and a humoral immune response?

  • option_A: Humoral immunity neutralizes extracellular virus, while cell-mediated immunity targets infected cells to prevent further neurological damage.
  • option_B: Cell-mediated immunity directly replaces damaged neurons, and humoral immunity prevents re-infection.
  • option_C: Both responses are needed for general immunity, but only humoral immunity protects against neurological damage.
  • option_D: The humoral response prevents the virus from entering the brain, while the cell-mediated response strengthens the blood-brain barrier.

Explanation

The polio virus initially replicates in the gastrointestinal tract and then can spread to the nervous system. Humoral immunity antibodies is critical for neutralizing the virus while it is still extracellular, preventing it from reaching and infecting neurons in the first place. Once neurons are infected, antibodies are less effective, and cell-mediated immunity cytotoxic T cells becomes crucial to identify and destroy infected cells, thereby limiting the spread of the virus within the nervous system and preventing further irreversible damage to neurons, which cannot be replaced.