PaBi (15): Immune evasion Flashcards
What stages of the immune system can parasites evade/ attack?
All of them, from antigen recognition to contraction and formation of memory
Why does the immune response need to be regulated?
Needs to balance killing the pathogen but not cause damage to the host by inflammation
What is involved in immune regulation?
Regulatory T and B cells, IL-10, TGFbeta
Why must the parasite avoid the immune response?
To survive and complete development, reproduce and ensure transmission to next host
What are 4 ways a parasite can evade the immune response?
Hiding, escaping, misdirection, disarming
Give examples of how parasites can hide from the immune system.
Molecular mimicry- either expressing or coating yourself in host proteins e.g. schistosomes mimic blood group antigens and T. cruzi mimic neuron surface molecules. Filarial nematodes produce CPI-2 which inhibits antigen processing, can inhibit class 2 MHC, maturation of APC or desensitise PRRs. PfEMP1 can inhibit antigen uptake.
How can parasites escape the immune system?
By changing their surface antigens e.g. T. brucei shedding it’s VSG coat when antibodies against it are produced, Plasmodium polymorphic surface antigens (PfEMP1), schistosomes (and other helminths) are covered with tegument which is regularly replaced.
How do parasites induce immune suppression?
Filarial nematodes favour a Treg response which shuts down Th cells. Intestinal nematodes secrete a TGF-beta mimic which up-regulates the production of Tregs.
Give an example of a parasite which uses immune redirection.
Trichuris muris is an intestinal helminth that requires a Th2 response to expel it. The parasite produces an IFN-gamma mimic to induce differentiation of T cells into Th1 instead of Th2.
What immune manipulators are secreted by helminths to disarm the immune system?
CPI-2 which inhibits antigen presentation and causes impaired T cell function, serpins which inhibit neutrophil function, ES-62 which inhibits T, B and innate cells, antioxidants which inhibit reactive oxygen species.
How does Leishmania disarm the immune response?
Produces anti-oxidases to inhibit oxidative burst by macrophages and inhibits complement by phosphorylating C3, C5 and C9
