Question

13. Natural infection with Vibrio cholerae results in the development of long-lived protective immunity: a. What is the basis of immunity (include the protective antigen in your answer)? (2 points) b. Provide an explanation why a live vaccine strain that lacks Toxin Co-regulated pili (TCP) does not provide effective immunity. (2 points) Name: c. A live vaccine strain lacking cholera toxin A-subunit still causes mild diarrhea. Provide an explanation and how you would use this information to construct a live, safe, and effective vaccine. (4 points)

Answer 1

13. a. The basis of immunity is the production of secretory Immunoglobulin A, Immunoglobulins G and M against the Lipopolysaccharide and outer membrane proteins. Here Lipopolysaccharide or LPS is the protective antigen.

b. A live vaccine strain lacking a Toxin Co-regulated Pilli (TCP) doesn't provide immunity. The immune system recognizes the colonization of the infecting Vibrio cholerae which is mediated by TCP. So in the absence of TCP, no colonization occurs and hence no immune response is elicited.

c. A live vaccine lacking cholera toxin A subunit still causes mild diarrhea. This could be due to the presence of another toxin and in this case it was identified to be Ace. Through genetic manipulation the gene coding for Ace can be deleted to produce safe recombinants which can be used to produce live, safe and effective vaccine