L22: Evolution of the immune system

Question 1

Relationships between organisms (3)

Answer 1

1. Symbiosis: both organisms benefit
2. Commensalism: one benefits and situation is neural for the other
3. Parasitism: one benefits and one suffers

Question 2

Immune system should … (3)

Answer 2

1. Eliminate or control parasites (pathogens)
2. Stop commensals or symbionts from becoming pathogens
3. Maintain healthy relationship with symbionts

Question 3

Mimivirus

Answer 3

Giant virus of amoeba. Seen with sputnik which infect cells by binding to outside of mimivirus, decreasing its fitness and causes defective mimivirus production.

Question 4

Invertebrate innate immunity

Answer 4

1. Have nothing similar to mammalian acquired immune system.
2. Invertebrates have roving phagocytes, pattern recognition receptors and antimicrobial peptide production
3. Elaborate innate immune pathogen recognition
4. Great variety of Nod-like receptors
5. Have more different TLR genes
6. May give great diversity in recognition of different PAMPS

Question 5

Acquired immunity

Answer 5

Receptor diversity + clonal selection + specificity + memory

Question 6

Jawed vertebrates - diversity of antigen receptors

Answer 6

Depends on RAG gene productions. Rag products mediate recombination of alternative DNA segments. Rag1/2 recognise recombination signal sequences, catalyse cleavage of DNA adjacent to V, D and J segements in TCR and BCR (Ig) genes

Question 7

Transposons

Answer 7

Mobile genetic elements which have inverted DNA repeats at each end, encode a transposase enzyme to cut DNA and excise the transposon.

Question 8

Animal ancestral to vertebrates events

Answer 8

1. Transposon inserts into a gene with Ig-like domains (precursor of BCR and TCR)
2. Terminal inverted repeats of the transposon, that are transposase cleavage targets could have evolved to give the RSS sequences
3. A transposon integrated in a different site provides the transposase genes which evolve into the RAG1/RAG2 gene locus
4. Rounds of duplication of regions of DNA ultimately generates the multiple V, D and J segments flanked by repeats

Question 9

Variable lymphocyte receptors (VLR) of jawless vertebrates

Answer 9

Have B/T-like lymphocytes:

1. T cell-like cells have VLRA proteins - not secreted
2. B cell-like cells have VLRB proteins - secreted like antibodies

Question 10

VLR generation of diversity

Answer 10

Generation of functional VLR genes:

1. During DNA replication when gene segments from flanking regions are copied into the gene
2. Rather than replicating DNA along the strand, the replication complex swaps templates to use a homologous region from elsewhere in the genome
3. Jump occurs a number of times, randomly selecting LRR gene segments to make up the VLR

Question 11

Control of Dengue Virus using Wolbachia bacterium

Answer 11

Wolbachia is a symbiotic bacterium, not infectious but maternally transmitted. Wolbachia infected mosquitoes have low Dengue virus replication.