How does the immune system recognise pathogens?

Ifeoma Ezepue
Flashcards by Ifeoma Ezepue, updated more than 1 year ago
Ifeoma Ezepue
Created by Ifeoma Ezepue about 4 years ago
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University Fundamentals of Medicine (Immunology) Flashcards on How does the immune system recognise pathogens?, created by Ifeoma Ezepue on 11/01/2015.
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Question Answer
What two things must the immune system do? What are the consequences if they are not done? recognise and respond to pathogens -death from infectious diseases not respond to component of our own bodies Paul Ehrlich - 'horror autoxicus' -not possible -auto-immune disease
What is an antigen? anything that binds to a specific receptor on an immune cell pathogens contain many antigens
What is an immunogen? anything that elicits an immune response most (but not all) antigens are immunogens
What is an epitope? the portion of an antigen that is recognised and bound by a receptor on an immune cell
Can you give an overview of antigen recognition? receptor binds to antigen signalling cascade initiated (changes what cell does) gene transcription production of effector molecules
Give some examples of cells that can be found in the adaptive and innate immune system adaptive -T cells, B cells innate -NK cells, monocytes/macrophages, granulocytes, dendritic cells
In terms of antigen recognition what is the difference between the innate and adaptive immune system? innate -few antigens can be recognised adaptive -millions+ of antigens recognised
Briefly describe the recognition of 'non-self' by innate immune cells pattern recognition receptors (PRRs) recognise pathogen associated molecular patterns (PAMPs) which aren't present in host cells e.g. cell wall, flagella
With innate immune cells there is an inherent lack of response to self (tolerance). Why is this? because the things the receptors recognise are absent from our bodies
What is an important example of pattern recognition receptors? Toll-like receptors 13 in mice 10 in humans
Describe the general process of adaptive immunity - how are large numbers of useful cells generated in response to an antigen? millions of different antigens to be recognised each new lymphocyte expresses just one type of receptor and recognises one antigen (specific) only a few of each of these lymphocytes antigen activates lymphocyte with 'right' receptor clonal expansion of these lymphocytes
Explain the recognition of B cells including the following key terms: Ig, BCR, epitope, antibody ARM used by B cell = immunoglobulin (Ig) membrane bound Ig = B-cell receptor (BCR) antigens recognised directly shape of epitope formed by protein folding B cell is activated and differentiates into plasma cells which secrete Ig (antibody) with specificity identical to BCR
Describe the structure of a typical antibody - draw and label a diagram 2 heavy chains (long) 2 light chains (short) ^identical to each other constant region - doesn't differ between different antibody molecules variable region - specific to antigen - where antigen binds structure held together by disulphide bonds
B cells can make different classes (isotypes) of antibody. What is the benefit of this? each antibody class can mediate different biological functions allows immune system to activate different immune mechanisms that may be more tailored to a specific problem
What are the different classes of antibody? Comment on their structure IgM - pentamer IgE - monomer IgG - monomer IgA - dimer
What special process can B cells undergo? a given B cell starts by making IgM but then switches to making IgG or IgA or IgE this is known as class switching
During the process of class switching what remains constant and what changes? antibody specificity remains constant biological effector functions vary
Which class of antibody is made first in an immune response? What happens next? What do the different levels of each type of class indicate? Include a diagram in your answer IgM class switching primary then secondary IgG made loads of IgM = recent infection loads of IgG = happened long time ago
With B cells how is receptor diversity generated? Explain in detail and include a diagram in your answer by random mixing and matching of variable, diversity and joining segments within the heavy chain and light chain loci known as somatic DNA recombination -B cell in bone marrow some DNA spliced out DJ recombination more splicing, V-DJ recombination transcription to make mRNA RNA splicing to make mature transcript translation and assembly of light and heavy chains
How do T cells recognise antigens? using a T cell receptor (TCR) antigen presenting cell e.g. dendritic cell, macrophage present antigen to T cell using major histocompatibility complex linear (peptide) antigens are recognised
Draw a diagram depicting the structure of the T Cell receptor (things to include is on answer flashcard) a chain b chain carbohydrate variable region constant region stalk segment transmembrane region cytoplasmic tail disulfide bond
When do T cells being to express TCRs? during their development in the thymus
The generation of TCR diversity also involves.... somatic DNA recombination
Define the term major histocompatibility complex the major genetic region that determines compatibility of tissues transplanted between individuals (whether or not tissues would be accepted or rejected)
Define the term HLA human leukocyte antigens name given to MHC molecules in humans
What are the two different types of MHC? What is the difference between them? MHC Class I -found in all cells -present antigen to CD8 cytotoxic T cells MHC Class II -found in APC only -present antigen to CD4 helper T cells
What can be said about the peptide binding by MHC molecules? peptide binding by MHC molecule is PROMISCUOUS bind to a range of peptide that can be accommodated in the groove (so not a specific peptide)
What determines the binding between MHC molecules and the linear peptide antigens? the fit between amino acid side chains in the peptide and pockets in the groove of the MHC molecule
The MHC has two properties that help ensure the maximum number of peptides can be presented. What are they? polygenic -more than on type of MHC class I and class II molecule highly polymorphic -multiple alleles in population means most people are heterozygous
One of the two major properties of MHCs may prove a barrier to organ transplantation. Which property is this and how does this act as a barrier? polymorphism different MHC molecules on the graft are recognized as foreign tissue rejected due to immune response
Explain the immunology of Coeliac disease. How common is the disease and what is it specifically? occurs in people carrying particular MHC class II molecules -HLA-DQ2 or HLA-DQ8 only these MHC molecules can present gliadin peptides in gluten to T cells to cause disease relatively common 1:200 Caucasians chronic inflammation of small intestine due to inappropriate immune response to wheat gluten
What is central tolerance? as T cells develop in the thymus and B cells in the bone marrow, their receptors are tested for reactivity to self antigens -if self-reactivity is too strong the lymphocytes are killed
What is peripheral tolerance? self-reactive lymphocytes that escape deletion during development can be controlled in the periphery by regulatory T cells - Treg
What is tTG and what does it do? enzyme tTG (tissue transglutaminase) modifies proteins deanimates glutamine to form glutamic acid when done in gliadin derived peptides increases their ability to bind to HLA-DQ2 example of positive reinforcement T cell activated produces lots of cytokines
What are three histological features of coeliac disease? villus atrophy crypt abscesses intraepithelial lymphocytes
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