Immune evasion Flashcards
What is a superantigen?
A type of toxin that is produced by gram positive bacteria which will bind MHC and TCR, even though the TCR does not have specificity for this antigen. Causes a “watered down” immune response
What immunomodulators do viruses secrete?
Cytokine inhibitors such as TND, IL-1beta, cytokine mimics (that are suppressor such as vIL-10), and complement inhibitors
How does the streptococcus pneumonia capsule evade immune responses?
It uses host hyaluronan from the extracellular matrix, which camouflages it
name a helmith that modulate its surface molecules and how it does it
Trypanosome steals glycosylates mucin domains and display it on its surface; different ones depending on which life stage (to mimic host).
Name two things Listeria does to inhibit phagocytosis
It lyses the phagocyte with a membrane attack complex and can also escape the phagosome
What are some ways do inhibit phagocytosis and which bacteria does them?
Kill the phagocyte (staphylococcus using leukocidins), lyse it (listeria; membrane attack complex), escape the phagosome (shigella, listeria), prevent phagosome-lysosome formation (chlamydia, legionella), survive in phagosome (salmonella)
Name molecules used by Staphylococci that inhibits the complement system
SpA, Efb, SCIN, SSL, CHIPS, staphylokinase
Which type of bacteria has bigger need of interfering with the complement system?
Extracellular bacteria
What is one way to prevent iNOS
Use L-arg to produce ammonia instead
The mechanisms of evading the immune system are remarkably similar between different types of pathogens, why do you think that is?
Yet, no pathogens have all mechanisms, why not?
Convergent evolution; they all target the same immune system. It would take too much energy to have all mechanisms, and they are not necessary for all lifestyles. For example an intracellular bacteria does need to survive in the phagosome, but not evade complement, while an extracellular bacteria needs to do otherwise.
What are the forms of surface variation?
Phase variation; the on-off switch of a surface antigen
Genetic drift; the random mutations in surface proteins
Antigenic variation; expressions of alternative forms of an antigen
How does viruses change surface proteins?
Genetic drift and genetic shift
Genetic drift
Random mutations in surface proteins cause surface variation. More common in viruses as they mutate a lot + rapidly
Genetic shift
Viruses variants of the same species with a lot of RNA strands can combine and reassort into a new strain (Influenza A)
How does bacteria change surface proteins?
Phase variations; genes are switched on and off (randomly). Can be both transcriptional or translational control
Gene conversion; have multiple silent cassettes for the same gene; can be segmented together
How does eukaryotic microbes change surface proteins?
RNAi
Chromatin structure
Nuclear localization; when its activated its in a special place in the nucleus
How does RNAi in antigenic variation?
miRNA, lncRNAs bind to RNA ot silence them ?
Name some genetic mechanisms that contribute to antigenic variation.
◦Point mutations
◦Multiple copies in the genome
◦DNA rearrangements
◦Transcriptional regulation
Name some epigenetic mechanisms that contribute to antigenic variation.
◦RNA Interference (RNAi)
◦Chromatin structure
◦Nuclear localization
How do pathogens inhibit the effects of nitric oxide (NO) or reactive oxygen species (ROS)?
Helicobacter pylori consumes L-Arg to produce ammonia, preventing iNOS from producing NO. Salmonella can block iNOS activation and prevent NADPH oxidase, thus reducing NO and oxygen radicals.
What is VSG and which pathogen utilizes it for antigenic variation
Variant surface glycoprotein (VSG) is a glycoprotein on the surface of Trypanosoma brucei that protects it and is subject to extensive antigenic variation.
What are VSPs and which pathogen utilizes them?
Variable Surface Proteins (VSPs) are a family of proteins used by Giardia intestinalis for antigenic variation.
What are the pros of glycosylated proteins?
Immunoglobulins, TCR etc recognize proteins, and if there is sugar on the proteins they can’t recognize them
