Adaptive Immunity I Flashcards
Describe the purpose of the innate immune system
- first line of defence- fast, nonspecific
- humoral and cell mediated
- activated within mins
- buying time for adaptive immune system to kick it
What do Primitive T cells do?
- recognise antigens similarly to the innate immune system
Describe the role of the adaptive immune system
- humoral and cell mediated (using B an T cells)
- slower to develop (5-6 days)
Which recognition molecules does the innate immune response use?
- germ line encoded pattern recognition receptors
- these bind to pathogen - and damage-associated molecular patters- generic molecules found on many different types of pathogen (e.g. LPS) or released in response to stess/ tissue damage
Which recognition receptors does the adaptive immune system use?
- randomly generated B and T cell receptors
- highly specific to individual antigen molecules, rather than generic molecules found on many pathogens
What cell produces antibodies?
- B cells
How can antibodies provide passive immunity?
- transferred between individuals
What is the difference between humoral immunity and cell-mediated immunity?
- humoral - antibodies
- cell mediated - involved primarily T cells
- these eradicate pathogens, clear infected self-cells, or aif other cells in inducing immunity
Fill in the gaps and describe the process
- only naive cells should be released into circulation
- continually circulate through body
- go into secondary lymphoid organs looking for their specific antigen
- if it encounters its antigen - clonally proliferates so more effective
- these cells will eliminate pathogen
- effector cells die
- left with memory cells
How do the innate and adaptive immune systems work together?
- dendritic cell key - initiates adaptive IS
- need the innate immune cells to sense the danger and to become APCs
- helper cells then produce cytokines that can help B cells and NK to form a better antibody response
What is happening here?
- primary response initiated upon first exposure to antigen
- memory lymphocytes left behind
- a second exposure to same antigen - stimulates memory cells
- reactivation yields a faster/ more effective reponse
- memory NOT present in innate immunity
Why are memory cells more effective?
- more of them
- more easily activated
- more effective
- reside in/ home back into the tissue where first infection occured
What forms may an antigen be in?
- protein, lipid, carb, nucleic acid or any combo of these
- foreign or altered self molecules
- soluble or particulate
- simple or complex
What is an antigen?
- a processed peptide derived from a foreign or alter self protein and presented by MHC I or II molecules
What do CD8/ CD4 T cells recognise peptides presented by?
- CD8 - MHC I
- CD4 - MHC II
What is the antigen receptor on B cells?
- membrane-bound form of IG secreted upon stimulation
Membrane bound IG =
Secreted IG =
- BCR
- antibody
Describe the structure of an antibody
- 2 heavy chains
- 2 light chains
- held together by intra/interchain disulfide covalent bonds
Label this
What is the function pf CH1 and CL domains?
- extend arms of the antibody away from hinge region
What is the function of the VH and VL domains?
- variable regions are made of Ig folds
- contain 3 hypervariable loops called CDRs
- produce ability of Ab to bind to its specific antigen
- each Ab can bind to 2 antigens
What is the function of the carboxyl-terminal domains?
- confers the effector activity of the Ab
- membrane-bound Ab has a hydrophobic tansmembrane segment and very short cytoplasmic tail
- secreted Ab is formed by alternative RNA splicing mechanisms that remove/ replace these regions
What is the process of signal transduction in B cells?
- BcR has v little cytoplasmic domain and cannot signal
- but complexes with 2 Igalpha and 2 Igbeta chains (CD79a + CD79b)
- Igalpha and Igbeta have signaling motifs in their cytoplasmic chains
- phosphorylation of the ITAMs triggers signaling cascades
- CD19 acts as a co-receptor further initiating the signaling pathways
What are TCRs?
- T cell receptors
- not Ig
- belong to the Ig superfamily
- possess V and C domains
- CDRs (complementary determining regions) are found on the variable regions of each chain- bind to MHC
- heterodimers (alpha and beta chain)
How do T cells signal?
- TCR cannot signal
- transduction is initiated through ITAMs expressed by chains of the CD3 complex
- T cell co-receptors CD4 and CD8 also bind to MHC to aid signal transduction
- CD28 involved
How can a limited amount of DNA genetic info produce an extensive variety of antibodies?
- B cells use groups of PARTS of genes to create different possible antibodies using recombination
Name the different gene segments used.
- Variable
- diversity
- joining
- constant
Which segment is used in antibody heavy chains only?
- D
What are the 2 types of light chains?
- kappa
- lambda
What happens if you change the heavy constant gene segment?
- change tail of antibody
- change the functional properties
- greater diversity of constant gene segment
Describe the mechanism of V(D)J recombination
- recombination is directed by signal sequences (RSSs) flanking each antibody gene segment
- gene segments joinedby the recombo activating gene recombinases RAG1/2
- RAG1 forms a complex with RSSs stabilized by binding RAG2
- +other proteins required
- V(D)J proteins results in functional Ig variable region gene
- RAG proteins bind and cleave the DNA
- other proteins process tha hairpin loops that form after RAG has done its job
- products include a recombines coding joint and a leftover signal joint that is later degraded
What are the 4 mechanisms that generate antibody diversity in naive B cells?
- Multiple gene segments
- nucleotides can be inserted between joints
- exonuclease trimming
- combinatorial diversity (which heavy chains pair with light chains)
What are the 2 receptors that thymocytes can express?
Which thymocyte receptor is more common in fetal development and how does this change?
- TCRygamma are more common
- but decrease after birth in mice
- (retained as a major pop in ruminants, pigs and chickens)
