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39 Cards in this Set
- Front
- Back
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Where do BCR's change to a secreted form (Ig)?
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Secondary Lymphoid Organs
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What's the difference, location wise, between BCR's and TCR's?
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BCR's are secreted as Ig's whereas TCR's remain on the cell
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How do BCRs and TCRs differ in their mechanism of antigen recognition?
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BCR: has two antigen binding sites
TCR: only recognizes antigen if digested and embedded in a peptide-binding cleft on the HLA class I or II molecule (MHC) |
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How would you characterize Myeloma proteins?
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Homogeneous Ig's produced by a single clone of malignant B cells (plasma cells)
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What are Bence Jones Proteins?
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light chain "dimers" in the urine of some patients with myeloma
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Describe the structure of an Ig molecule?
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- 2 heavy chains
- 2 light chains N-terminal w/ variable regions C-terminal w/ constant regions |
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What segments does papain cleave an Ig into?
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- 2 identifical Fab fragments
- a single Fc fragment (cleaves disulfide bonds in the hinge region) |
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What segments does pepsin cleave an Ig into?
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- one F(ab')2 molecule
- Fc fragment degraded into smaller peptides) |
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1. What does the Fab fragment do?
2. What does the Fc fragment do? |
1) binds antigen
2) bind macrophages, mediates biological activity w/ phagocytic cells |
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Significance of the reducing agent studies that dissolved all the disulfide bonds?
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established the existence of 2 heavy (H) and 2 light (L) chains in the Ig molecule
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What two parts of the Ig form the pocket that binds an antigenic epitope?
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VL and VH
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What binds complement and mediates ADCC?
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Fc portion of IgG (CH2 and CH3)
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Which Ig's have a CH4 domain?
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IgE and IgM
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What do hinge regions do and what are they made of?
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Provide flexibility, contain proline and cystines
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What region of the Ig is glycosylated?
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CH domains
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1. What are the most variable regions called?
2. What are the less variable portions of the V-regions? |
1. Complementarity Determined Regions (CDR's)
(These are the contact points with the antigen) 2. Framework regions |
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What are the five flavors of Ig's/types of heavy chains?
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M, G, A, D, E
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Which Ig's lack a hinge region?
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IgM and IgE
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Which Ig contains a J chain?
Which Ig contains an SC segment? |
- IgA and IgM
- IgA |
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1. Which Ig's are found in blood?
2. Tissue fluids? 3. Secretions 4. Fetus 5. Under epithelium 6. Brain 7. Respiratory mucosa |
1. IgG and IgM
2. IgG 3. IgA 4. IgG (passive from mom) 5. IgE 6. No IgE 7. IgD |
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Characteristics of IgG
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- long half life
- secreted during late primary or early secondary response - activates complement - opsonizing antibody - neutralizes toxins and viruses |
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Characteristics of IgM
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- first Ig to appear during ontogeny and during immune response
- most effective complement activator - natural isohemagglutinin (anti-AB) |
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Characteristics of IgD
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- second receptor on B cell surface
- sensitive to proteolysis - respiratory mucosa - binds to mast cells an basophils - triggers inflammatory burst releasing IL-1, TNF |
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Characteristics of IgE
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- reaginic antibody - binds to basophils, mast cells etc
- lowest concentration in serum - short half life - alergy and anaphylaxis - protection against parasites (worms), acute inflammatory response |
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Characteristics of IgA
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- dimer in secretions, monomer in serum
- two subclasses - short half life - major Ig in the body - major Ig in external secretions (saliva) - protects all mucosal surfaces from pathogens |
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Which Ig does NOT recruit inflammatory mediators, fix complement, or mediate ADCC?
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IgA
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What does the secretory component do? (2)
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1. protects IgA from proteolysis
2. facilitates IgA attachment to epithelia so Ags can be trapped in mucus where proteases can degrade IgA-Ag complexes |
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What is the major congenital immunodeficiency in humans?
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IgA deficiency
--> microbes can enter the body, not trapped at epithelia, local infections (systemic infections are NOT a problem) |
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Describe the synthesis of IgA
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- IgA dimers secreted by plasma cells in the lamina propria or Peyer's patches
- bound by poly-Ig receptors on epithelial cells lining the gut - dimer pinocytosed into cell, trafficks across - exocytosed into lumen where a portion of poly-Ig receptor remains attached to IgA (become SC) and rest is destroyed |
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How do the J chain and secretory component (SC) differ in where they are added to the IgA dimmer?
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J-chain: plasma cell
SC: epithelial cell |
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What do FcRns and FcRps do?
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control levels of IgG, located on endothelial cells lining blood vessels
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Describe IgG processing:
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IgG enter vascular endothelial cells by pinocytosis, vesicles fuse with endosome, binds FcRns at low pH, recycled to serum via vesciels
IgG is released at high pH of serum |
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Difference between isotypes, allotypes, idiotypes
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isotype - determine the class of Ig by different constant regions of the heavy chains
allotype - allelic forms of the same protein that vary withIN same species idiotypes - in variable regions of the heavy and light chains of the Ab (serves as a clonal marker of the B-cell that originally made an Ig) |
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Characteristics of TCRs
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- remains on the surface of the cell
- kill infected cells (CTLs) - produce cytokines - see processed Ag in grooves of MHC, never free antigens |
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How does the C terminal of TCR differ from BCR?
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TCR C-terminal does NOT extend into the cytosol of the cell
- relies on a series of other molecules to signal (CD3, 2 pairs) |
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Where as aB vs. yG TCRs expressed?
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aB: throughout body (conventional and NKT cells)
yG: skin, mucosa, gut |
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What is another presenting molecule other than MHC that T-cells can recognize?
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CD1 molecules that present lipid
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SCID: genetic mutation?
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ZAP-70, CD3, Rag
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DiGeorge: genetic mutation?
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22q11, 10p
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