Answer:
The mutated cystic fibrosis transmembrane conductance regulator (CFTR) blocks the entry of <em>Salmonella typhi</em> into the epithelial cells.
Explanation:
Cystic Fibrosis Transmembrane Conductance Regulator (CFTR):
CFTR is a membrane protein and a chloride channel that regulates the influx and eflux of chloride ions. Cystic fibrosis is a disorder that occurs due to the presence of two recessive alleles in an individual.
Background:
In terms of immunology and defense against infectious disease, CFTR acts as a receptor for the bacteria, <em>Pseudomonas aeruginosa, </em>which is the leading cause of infections in CF patients<em>. P. aeruginosa </em>binds to normal CFTR receptors and is effectively removed from the body. But a mutated CFTR cannot bind the bacteria effectively, leading to life long <em>P.aeruginosa </em>infections.
Mutated CFTR Immune to <em>Salmonella typhi:</em>
<u><em>Salmonella typhi </em></u><u>enters the body by binding to the CFTR receptor</u><u>.</u> As a natural defense mechanism, <em>S. typhi</em> binds to CFTR on the epithelial cells of the GIT, which, in turn, engulf the bacteria and then slough off from the lining. But, a severe attack leaves the lining open for attack as the epithelial layer sloughs off.
A mutated or missing CFTR receptor is unable to effectively bind to <em>S. typhi</em>; leaving the carrier of the mutated CF allele immune to typhoid infections.