antibodies Flashcards
what are antibodies produced by?
B cell lymphocytes
where do lymphocytes originate from?
where do they migrate to?
- lymphocytes arise from stem cells in bone marrow and differentiate in the central lymphoid organs (red):
- B cells in the bone marrow
- T cells in the thymus
- they migrate in the bloodstream to peripheral secondary lymphoid organs (yellow), lymph nodes, spleen, gut-associated lymphoid tissue (GALT), peyers patches, tonsils, appendix
where do naive B cells circulate?
where is the main site of antigen encounters?
what do lymphatics do?
where do recirculating B cells enter back into the blood stream?
- naive B Cells: B cells that have not met the antigens, circulate from blood into peripheral lymphoid tissues
- peripheral lymphoid tissues are the main site of antigen encounters
- lymphatics drain tissues of fluid, through the lymph nodes and into the thoracic duct
- recirculating B cells enter back into the bloodstream by the thoracic duct
lymph node organisation:
how are lymph nodes organised?
when do germinal centres form?
what does the medulla consist of?
how do antigens enter?
- organised into cortex and inner medula
- cortex has an outer section of B cells organised into follicles (yellow) and a paracortical area of T cells and dendritic cells (blue)
- germinal centres of B cell proliferation form during an immune response
- medulla consists of macrophages and antibody secreting B cells (plasma cells)
- antigen (in Dendritic cells) enter through afferent lymphatics
spleen: the spleen is organised into red pulp and white pulp
what is red pulp the site of?
what is white pulp?
where does blood carrying lymphocytes and antigens enter?
- red pulp is the site of Red blood cell destruction
- white pulp is lymphoid
- blood carrying lymphocytes and antigen enter from a trabecular artery into a central arteriole
- they an then pass into a marginal sinus and exit through a trabecular vein
- the marginal sinus is surrounded by lymphocytes and within it is the periarteriolar sheath (PALS) made up of T cells - B cell follicles and a B cell corona also form
- antigen enters from blood rather than lymph
antibodies:
how is the secondary response in comparison to the primary response?
the secondary (memory) response is faster, can produce more antibodies and does not prevent you from making a response to another antigen
antibodies;
what are the two functions of antibodies?
what are antibodies made of?
- Ab have two separate functions:
1. firstly to bind the pathogen that elicited its production
2. secondly to recruit other cells and molecules that will lead to clearance or destruction of the pathogen. - Ab are made of four polypeptide chains, two identical heavy (H) chains and two identical light chains (L)
- The H chains are disulfide bonded to each other, and each H chain is also disulfide bonded to a L chain
- this results in two identical binding sites
- Two L chain exist, lamba and kappa. Any individual Ab has either lamba or kappa, never a mixture of each. In human the ratio is 2:1 in favour of kappa
where is the binding site for the antigen on the antibody? and what do the other regions of the antibody do?
why are Fab fragments useful?
what does the back end of the antibody do (Fc region)?
what does the front end (Fab regions) do?
the binding site for antigen is contained in the Fab region (front end), whilst the Fc region performs many of the functions of antibodies; interacting with receptors etc. (back end)
fab and F(ab) 2 fragments are very useful tools in the laboratory ie. can be used to label cells without inducing the effects of the Fc region, or in the case of Fab fragments, inducing receptor triggering or internalisation by crosslinking
- back end (one head) activates compliment (a cascade of proteins present in your serum that can kill pathogens and lead to that clearance) (see innate immunity lecture)
- front end (two heads) is what binds onto the antigen (the pathogen) the ‘Baddie’
what determines hypervariability in V domains?
what is the final specificity of the antigen determined by?
- three hypervariability loops determine antigen specificity by forming a surface complimentary to the antibody
- final specificity is determined by a combination of loops from H and L chains, and not either alone
in what three ways can antigens bind to antibodies?
- antigens can bind in pockets or grooves, or on extended surfaces:
- A) small peptide bound in pocket
- B) extended peptide from HIV protein bound in groove
- C) extended surface interaction of An with hen egg-white lysozyme
what 4 things create antibody diversity?
- chromosomal rearrangement (reaaranging multiple gene segments)
- junctional diversity
- different combinations of H and L chains
- somatic hypermutation
what is junctional diversity?
- junctional diversity is when N-nucleotides (non-template encoded nucleotides) are added by terminal deoxynulceotidyl transferase (TdT)
- after up to 20 nucleotides are added, pairing is attempted, followed by trimming off non-matching bases, filling gaps and ligation to complete
what is somatic hypermutation
-somatic hypermutation, occurs after B cells have become antigen activated in the lymph node
- during the course of a immune response, mutations accumulate in the V regions of the H and L chain genes
- some of these will bind antigen better and these cells are selected to expand and secrete antibody - this is called affinity maturation
what are the 5 classes on antibody defined by?
what are the 5 classes of antibody?
what does each antibody do?
they are defined by their heavy chain
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- IgG - gamma HC - elevated in bloodstream means sign of infection - when B cells are activated, the IgM and IgM transmembrane proteins switch to IgA or IgE or IgG (secreted form)
- IgM - micro HC - expressed on the surfaces of unactivated B cells as transmembrane proteins
- IgD - delta symbol - also expressed on the surfaces of unactivated B cells as transmembrane proteins
- IgA - alpha HC - present in mucosal surfaces - when B cells are activated, the IgM and IgM transmembrane proteins switch to IgA or IgE or IgG (secreted form)
- IgE - epsilon HC - drives allergic responses, sits on mast cells in mucosal surfaces - when B cells are activated, the IgM and IgM transmembrane proteins switch to IgA or IgE or IgG (secreted form)
what do IgG (gamma HC) antibodies do?
IgG - gamma HC - elevated in bloodstream means sign of infection - when B cells are activated, the IgM and IgM transmembrane proteins switch to IgA or IgE or IgG (secreted form)
what are the steps of IgA secretion?
- binding of IgA to receptor on basolateral face of epithelial cell
- receptor-mediated endocytosis of IgA
- transport of IgA to apical face of epithelial cell
- cleavage of receptor releases IgA dimer from cell
what two antibodies dominate in plasma?
what are the main isotypes in extracellular fluid?
what dominates secretions across epithelia?
how does a fetus receive IgG antibodies?
where are IgE antibodies found?
- IgG and IgM predominate in plasma
- IgG and monomeric IgA are the main isotypes in extracellular fluid
- dimeric IgA predominates in secretions across epithelia, including breast milk
- the fetus receives IgG by transplacental transfer
- IgE is found mostly near to epithelial surfaces, especially gut, lungs and skin
antibody function:
describe the 5 steps of promoting antigen phagocytosis?
- antibody binding to bacterium
- antibody-coated bacterium binds to Fc receptors on cell surface
- macrophage membrane surrounds bacterium
- macrophage membranes fuse,creating a membrane-bounded vesicle the phagosome
- lysosomes fuse with the phagosome, creating the phagolysosome
what is a monoclonal antibody?
how are they made?
they are artificial lab produced antibodies
- each B cell makes only one type of antibody
- when fused with a type of cancer cell called a myeloma cell, this forms a fuse cell
- these grow and become immortal cells which pump out antibodies
