Antigenic Diversity Flashcards
What is a bacterial defense against a host’s mechanical cleansing?
adherence
What 2 things does adherence require?
- host receptor
- bacterial adhesin
What is the surface protein structure of an adhesin? (2 parts)
- pilus (fimbria) for attachment at a distance
- non-fimbrial adhesin (outer membrane protein for intimate attachment)
How does Neisseria gonorrhea avoid the immune system?
by varying its adhesin composition
What is meant by “host range” in adhesin diversity?
a specific adhesin exists for a specific host receptor (ex: N. gonorrhea adhesins differ in vagina vs. rectum)
Provide an example of how environmental conditions influence adhesin diversity.
Uropathogenic E. coli express Type I pili in the bladder (liquid) and Type P pili in the kidney (solid surface). So, you would want to target Type I pili for a bladder infection and Type P pili for a kidney infection. Promoters for each are turned on under a certain set of environmental factors.
Antigenicity of N. gonorrhea pili depends upon what?
the sequence of pilE
How is N. gonorrhea able to vary its pili antigenicity so much in the first place?
Each N. gonorrhea cell possesses genetic info for a large # of variant pilin proteins; thus, each cell can produce progeny that synthesize pili with different epitopes than its parent.
What is the function of pilS genes?
They are silent genes (lack of promoter, incomplete) that function as donor genes for recombination into pilE locus (and thus provide a source of sequence diversity for pilE locus).
Despite there only being 8 or 9 different types of pilS, why are antigenic possibilities infinite?
This is because during homologous recombination, strand invasion occurs; this causes hybrids to be made each time recombination occurs. The hybrids continue to accumulate over time. Daughter cells will always have different antigenicity than mother cells.
What are the mechanisms by which antigenic variation is achieved?
- Gene conversion (most common)
- Transformation (rare)
