BIO 343 Lecture 13: Chapter 13 Notes
Immunology Chapter 13: Failure of the Body’s Defenses
Hayden Casassa
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• Failures i the Bod’s Defeses
o Evasion and subversion of the immune system by pathogens
▪ Successful pathogen must avoid immune clearance... at least long enough to propagate and
spread
o Inherited deficiencies of the immune system
o Acquired immune deficiency system
• Antigenic Variation
o Ability of infectious pathogens to escape immune surveillance by varying the antigenicity of their
surface molecules
• Three main forms of Antigenic Variation
o Genetic variation within a species (strain/serotype differences)
o Mutation and Recombination (Influenza)
o Gene Rearrangement via Gene Conversion (Trypanosomes)
• Generic Variation within a species can prevent effective long term memory
o Some pathogens like S. pneumoniae evade immunity by simply existing as numerous different
strains or serotypes
o Each strain differs in its antigens expressed on the outer surface
• S. Pneumoniae
o Bacteria has polysaccharide capsule that makes them resistant to phagocytosis
o Effective elimination requires opsonizing antibodies that facilitate phagocytosis
• Protective immunity against S. Pneumoniae is strain or serotype specific
o Capsule type affects virulence, prevalence, and extent of drug resistance
o A’s ade agaist oe strai are’t effetie agaist others
• Some viruses undergo antigenic variation by mutation and recombination (Influenza)
• Influenza is an RNA Virus that infects respiratory epithelia
o Influenza A virus is broken into 2 glycoproteins called Hemagluttenin (H) and Neuraminidase (N)
which are used to attach to host cells
▪ Protective Abs are typically made to these envelop proteins
• Long-term survival of virus is ensured by generation of new viral strains that evade protective immunity
generated during past infections
o Type of Viral evolution is called Antigenic Drift and is caused by point mutations in viral RNA
genome
o This causes the yearly epidemic because RNA polymerase is notorious for making lots of mistakes
o Degree of immunity will vary based on previous exposure to viral epitopes
• Antigenic Drift (Picture below to left)
o Caused by point mutations in H and N genes due to error prone RNA Polymerase
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