Lecture 4: How organisms evade immune system Flashcards
How organisms evade immune response?
- Change in major B cell or T cell epitope, to escape immunological memory
- A large number of serotypes, varying in key determinants
- Bacterial capsule inhibits phagocytosis:
- Products which inhibit immune system:
what is an antigenic drift?
A minor genetic change from random point mutation that occurs as viruses replicate and evolve. Often results in changes in antigenic structure (e.g., hemagglutinin and neuraminidase in influenza virus) that cause epidemics.
what is an antigenic shift?
An abrupt, major change in a viral genome caused by exchange of genetic segments (reassortment) when two subtypes of a virus infect the same cell. Can increase the potential of a virus to cause pandemics, particularly if human pathogenic and animal pathogenic viruses exchange genetic information.
- -Two subtypes of viruses infect the same cell and exchange genetic segments (reassortment) to create new subtypes (e.g., H3N1 → H2N1).
- -Occurs in particular when human pathogenic and animal pathogenic influenza viruses exchange genetic information
what is the viral reassortment
Occurs in viruses with segmented genomes (e.g., influenza, rotavirus)
Exchange of genetic material between segments of two viruses from the same strain
Causes antigenic shift, which significantly increases the potential of a virus to cause pandemics
how EBV inhibits multiple immune functions?
- Produces IL-10-like protein.
- Inhibits Th1 & CTL development
- Polyclonal B cell expansion
what is the opsonization?
A process by which pathogens and immune complexes are marked with an opsonin (e.g., complement factor C3b) for phagocytosis, after which the pathogen can be eliminated by phagocytes that express opsonin receptors, e.g., Fc receptor and complement receptor 1.
what are the decoy molecules that help to evade the immune system?
MALARIA & DECOY MOLECULES
• Malaria proteins secreted
• “Mops up” antibody
• Complement activated at a safe distance from the organism
• Antibody bound to decoy does not kill or opsonize organism
what is the Antigenic variation during the life cycle of microorganisms that helps to evade immune system?
Antigenic variation or antigenic alteration refers to the mechanism by which an infectious agent such as a protozoan, bacterium or virus alters the proteins or carbohydrates on its surface and thus avoids a host immune response. Antigenic variation not only enables the pathogen to avoid the immune response in its current host but also allows re-infection of previously infected hosts. Antigenic variation can result from gene conversion, site-specific DNA inversions, hypermutation, or recombination of sequence .cassettes.
what microorganisms display antigenic variation?
Trypanosoma brucei Plasmodium falciparum Influenza HIV flaviviruses
how microorganisms Inhibition of complement deposition:
- Gram+ have a thick outer coat
- The capsule can prevent C3 binding receptor
- Cleavage of complement components
- Long-chain peptidoglycans - complement activated at a safe distance
what is the role of long-chain peptidoglycans in evading immune system?
complement is activated at a safe distance
what are the other ways by which the organism evades the immune response?
- Inhibition of complement deposition
- The organism remains latent in the immunologically-privileged site (HSV in trigeminal ganglion)
- Attack the immune system:
example of a virus that establishes latency to evade the immune system
HSV in trigeminal gnaglion
what is the immune difference in lepromatous vs tuberculoid leprosy?
1)lepromatous
Th2 response →
Reciprocal inhibition of Th1 response →inadequate cell-mediated immune response → many lepra bacilli
↑ Antibody production (hypergammaglobulinemia);
Nerve lesions are the result of the M. leprae invasion.
M. leprae grows best at cool sites in the body (skin, mucous membranes, peripheral nerves, anterior chamber of the eye, upper respiratory tract, testes).
2)tuberculoid
Th1 response →
Strong cell-mediated immune response → granuloma with epithelioid cells and lymphocytes but few or no lepra bacilli
Nerve demyelination is the result of a T-cell mediated response.
in what kind of infections investigate for immunodeficiency?
Serious
Persistent
Unusual organism/site
Recurrent
