Immunology Exam 2

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113 Terms

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resting B cell

naïve- never seen antigen that it recognizes

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Where are B cells found?

lymphatic system

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Where do B cells arise from?

pluripotent hematopoietic stem cells in bone marrow give rise to common lymphoid progenitor cells

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What are antigen binding sites made up of?

variable region of a light chain and the variable region of the heavy chain

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isotypes of heavy chains

G, M, A, D, E

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isotypes of light chains

kappa, lambda

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hypervaraiable regions

areas where the amino acid sequence differs the most between antibodies

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epitope

part of an antigen where antibody binds

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multivalent antigen

any antigen that contains more than one epitope (can be copies of same epitope)

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linear epitope

amino acids are adjacent (denatured protein can still be used)

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discontinuous epitope

amino acids that are not adjacent

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invitro vaccine

linear epitope is best bet

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Monoclonal antibody steps

  1. immunize mouse w/ antigen

  2. screen via ELISA to ID mouse

  3. kill mouse, harvest spleen, make a paste

  4. isolate B cells

  5. fuse B cells w/ myeloma cells —> hybridoma

  6. dilute into 1 cell per well in a 96-well plate

  7. screening (ELISA) to find right hybridoma

  8. take right hybridoma and mass produce

  9. purify antibody

  10. make $$$

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light chain V region

V (variable) and J (joining)

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heavy chain V region

V (variable), D (diversity), and J (joining)

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light chain gene segment

L (leading), V (variable), J (joining), C (constant)

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heavy chain gene segment

L (leading), V (variable), D (diversity), J (joining), C (constant)

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each V, D, J segment is flanked by _________ __________ ___________ that direct recombination

recombination signal sequences (RSS)

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RAG

recombination-activating genes

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RAG _____ and ______ your DNA; the DNA left in the middle is eventually degraded

cut; paste

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recombination enzymes

  1. RAG binds to RSSs, brings them together forming hairpin loop

  2. RAG cleaves DNA at specific sequences, removing the hairpin loop and adding P nucleotides

  3. terminal deoxynucleotidyl transferase (TdT) randomly adds N nucleotides

    1. addition of P and N nucleotides = junctional diversity

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rearrangement of VDJ segments produces a functional ______ chain gene

heavy

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random V, D, J explains:

diversity in B cells; can build functional proteins or not

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allelic exclusion

even though every B cell has two copies or alleles of the heavy/light chain locus, only one of each are rearranged to produce functional genes

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naive B cell circulates until it comes into contact with the _______ (hopefully on a pathogen) that it recognizes

antigen

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immunoglobulins are 1st made as _______________ on B cell surface; after exposure to antigen, Ig are produced in _________ form (antibodies)

membrane-bound; secreted

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somatic hypermutation

random point mutations introduced at a high rate in V domain

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point of mutations and diversifications of antibodies after antigen exposure

affinity maturation

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isotype switching

produces Ig with different C regions but identical antigen specificities; happens via more recombination at switch sequences

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IgM function

really good at activating complement through the classical pathway

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IgM unique properties

1st expressed as BCR; always 1st antibody to be produced

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IgD function

sensitization of basophils during resp bacterial infections

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IgD unique property

relatively rare

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IgG function

opsonization, neutralization, sensitizing NK cells

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IgG unique property

only antibody that can cross placenta

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IgA function

neutralization

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IgA unique property

found in mucosal secretions

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IgE function

activates mast cells

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When do B cells develop?

Birth— death

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H chain gene development in B cells

(stem cell) germline, (early pro-b cell) D-J rearrangement, (late pro-B cell) V-DJ rearrangement, (large & small pre-B cell, immature B cell) VDJ rearranged

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L chain gene development in B cells

(stem, early & late pro-b, large pre-B cells) germline, (small pre-B cell) V-J rearranging, (immature B cell) VJ rearranged

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Ig status in B cells

(stem, early & late pro-b cell) none, (large pre-B cell) micro heavy chain is made, (small pre-B cell) micro chain in endoplasmic reticulum, (immature B cell) micro heavy chain, lambda or kappa light chain, IgM on surface

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early B cell development dependent on BM ______ cells

stromal

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checkpoints in B cell development

  1. late pro B cell stage- formation of functional pre-BCR or not (functional heavy chain)

  2. small pre B cell stage- successful light chain rearrangement

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immature B cells tested on _____ ______ for self affinity

bone marrow

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if B cells have self affinity for bone marrow then ______

receptor editing (light chain editing only)

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B cell receptor editing occurs until:

no self affinity or runs out of DNA

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3 fates for self-reactive B cells

  1. survive through receptor editing

  2. die by apoptosis

  3. become anergic (nonresponsive to antigen) (1-5 day lifespan)

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developing B cells leave the BM, circulate between blood, ________ lymphoid tissues, and lymph

secondary

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final stage of B-cell maturation occurs in _______ _______

lymph nodes

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encounter with antigen leads to ________/________ B cells

activated, differentiated

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Where do T cells develop?

thymus

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When do T cells develop?

birth-involution

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involution

thymus shrinks w/ age

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What does the thymus become after involution?

adipose tissue

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stages of T cell development are characterized by ____ and _____ expression

CD4, CD8

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progenitor cells that enter the thymus are not yet committed to the ___ cell lineage

T

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upon interaction with thymic stromal cells, the progenitors are signaled to ______ and _______

divide, differentiate

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it is a race to rearrange lambda, delta, or beta 1st and once successful:

cells express both CD4 and CD8

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T cell development

  1. lymphoid progenitor cells enter thymus

  2. double - T cell progenitor

  3. beta chain rearranged

  4. Pre-TCR checkpoint (Beta chain and surrogate alpha chain)

  5. CD4 and CD8 expression turned on

  6. alpha chain rearranged

  7. TCR checkpoint (still double +)

  8. positive selection (MHC compatibility, single +)

  9. negative selection (self-reactive T cells die)

  10. mature T cells exit thymus

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checkpoints in T cell development

assembly of pre-TCR- alpha and beta chains are equal in size

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central tolerance maintained by ___ and ___ selection

+, -

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T cells that recognize self MHC molecules are ____ selected in the thymus

+

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__ selection determines expression of either CD4 or CD8 co-receptor

+

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receptor binds self-peptide: self-MHC I =

CD8 T cell

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receptor binds self-peptide: self-MHC II =

CD4 T cell

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tissue specific proteins are expressed in the thymus and participate in ___ selection

-

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transcriptions factor called ____ causes peripheral tissue proteins to be expressed by thymic epithelial cells

AIRE

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T cells that strongly recognize self antigen are deleted from the population

negatively selected

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T cell receptor structure

resembles a membrane-bound Fab fragment of Ig

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TCR diversity is generated by ______ ___________

gene rearrangement

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genetic defects in RAG can lead to

severe combined immunodeficiency syndrome (SCID)

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expression of TCR on cell surface requires association with additional ______

proteins

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MHC I—> CD8 T cells:

intracellular pathogens

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MHC II—> CD4 T cells:

extracellular pathogens

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MHC I is always expressed by

nucleated cells

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when nucleated cells are not infected by a virus they present ____

self

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MHC II always expressed by

macrophages and dendritic cells

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MHC I structure

shorter peptides, 3 large alpha chains, tiny beta chain, CD8 binds the alpha3 domain

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MHC II structure

longer peptides, equal alpha and beta chains, CD4 binds the beta2 domain

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MHC has ______ binding specifcity

promiscuous

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intracellular pathogens are degraded by

cytosol

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peptides generated in the cytosol are transported into the ___ where they bind MHC I

ER

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MHC I antigen processing

  1. sources of cytosolic antigens- self or pathogens

  2. proteasome degrades cytosolic proteins

  3. transport of peptides from the cytosol to the ER (TAP)

  4. assembly of peptide- MHC I complexes in ER

  5. surface expression of MHC I peptide complexes

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IFNg causes proteasome to favor production of _____ that bind MHC I

peptides

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class I heavy chain is stabilized by ______ until B2-microglobulin binds

calnexin

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calnexin is released and the heterodimer of class I heavy chain and B2m forms the

peptide-loading complex (calreticulin, tapasin, TAP, ERp57, and PDI)

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a peptide delivered by TAP binds to the class I heavy chain, forming

mature MHC class 1 molecule

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MHC I dissociates from the peptide-loading complex and is exported from

endoplasmic reticulum

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extracellular pathogens are _____ and ______ in the phagolysosome

phagocytosed, degraded

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peptides presented by MHC II are generated in ________ intracellular vesicles (__________)

acidified, phagolysosome

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certain pathogens (_______) hide out and replicate in these vesicles

mycobacteria

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MHC II antigen processing

  1. uptake of extracellular proteins into vesicular compartments of APCs

  2. processing of internalized proteins in endosomal and lysosomal vesicles

  3. biosynthesis and transport of MHC II molecules to endosomes

  4. association of processed peptides with MHC II molecules in vesicles

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MHC II molecules are prevented from binding peptides in the ____ by the ______ chain

ER, invariant

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vesicle:

MHC II, invariant chain stabilizing, HLA-DM (helper protein)

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most of invariant chain degraded with ____ left over

CLIP

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phagolysosome and ________ peptides fuses w/ vesicle

extracellular

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pH change down activates _______ removes CLIP so peptides can bind

HLA-DM

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alpha chain, beta chain, and peptide —>

gets shipped to plasma membrane

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MHC II expressed by

professional antigen presenting cells (B cells, macrophages, dendritic cells)