Evolution of the immune system Flashcards
what is comparative immunology?
the study of genetically diverse organisms and their relation to each other
what has comparative led to?
Toll-receptors in fruit flies
Toll-like receptors in mammals
what are some simple animal models to study immune response to infection?
wax worms
zebra fish
mice
what is a VLR?
variable lymphocyte receptor
- found in Agnathans- hagfish and lampreys (jawless fish)
- similar function to toll like receptors
why did adaptive immunity evolve in jawed fish?
-jaws allow increased prey range, but increased exposure to infection
-Skeletal meals increase risk of gut and mucosal tissue perforation
-Increased life span of jawed fish, greater chance of infection during long reproductive lifetime
what is whole genome duplication?
Extra copy of the genome
- genes are available to drift and take on new functions
how does whole genome duplication effect evolution?
Genome duplications are accompanied by morphological and functional innovations
Genetic changes in a copy of a gene will allow diversification of function in new paralogue
how do paralogues controbute to the development of the immune system?
form the basic of the MHC system
what allowed the emergence of the Generation of Diversity?
an ancestral RAG insertion
what is a RAG?
RAG is a recombinase activating gene that catalyses Ig recombination
what is Ig recombination?
recombination of genetic sequences
- are necessary for TCR and BCR rearrangements
how do transposons insert into host DNA?
Transposons encode for enzymes (transposases) that allow them to move and integrate sequences recognised by the transposase
- the transposase cleaves host DNA and inserts the transposon
how have transposons affected the evolution of immunoglobulin?
During the evolution of the immunoglobulin and TCR loci, rearrangement of the integrated transposon has separated the integration sites from the transposase genes
how did Agnathans develop their own immune system?
they split from other vertebrates before development of the immunoglobulin-based adaptive immune system
- they have their own immune system that was developed from distinct building blocks called leucine-rich ‘variable lymphocyte receptor’ proteins (VLR)
what produces a complete VLR gene?
The non-coding VLR gene undergoes recombination and produced the complete gene which then codes for VLR receptors
what type of immune cells to jawless fish have?
Both ‘B’ and ‘T cell’ like immune cells
what is the role of Drosophila DSCAM molecule?
- involved in ‘neuronal wiring’
- but also in host defense, DSCAM opsonizes bacteria to facilitate uptake by phagocytes
what does a diversification mechanism need to be?
Clonal
-cannot be a response from one cell otherwise it would not be sufficient to facilitate an immune response
what needs to happen for immune response to be specific?
there need to be a recombination event to produce different molecules with different responses to antigen/foreign material
would vaccination be effective in insects?
DSCAM generates diversity but little evidence for clonal selection for cells producing ‘useful’ atlternative transcripts
would vaccination of sea urchin be effective?
Multiple TLR, but expression probably not clonnally distributed. -All lymphocytes express the TLR
what is the best way to test for a memory immune response?
through immunization
what does a memory immune response mean is occurring in the organisms?
clonal selection
- selecting one type of antigen receptor over another during a response that is then retained.
what are the features of an adaptive immune system?
- diversity generation mechanism
- clonal expansion mechanism
- Memory (e.g. long-lived T and B cells, memory cells)
