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39 Cards in this Set

  • Front
  • Back
Where do BCR's change to a secreted form (Ig)?
Secondary Lymphoid Organs
What's the difference, location wise, between BCR's and TCR's?
BCR's are secreted as Ig's whereas TCR's remain on the cell
How do BCRs and TCRs differ in their mechanism of antigen recognition?
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)
How would you characterize Myeloma proteins?
Homogeneous Ig's produced by a single clone of malignant B cells (plasma cells)
What are Bence Jones Proteins?
light chain "dimers" in the urine of some patients with myeloma
Describe the structure of an Ig molecule?
- 2 heavy chains
- 2 light chains

N-terminal w/ variable regions
C-terminal w/ constant regions
What segments does papain cleave an Ig into?
- 2 identifical Fab fragments
- a single Fc fragment

(cleaves disulfide bonds in the hinge region)
What segments does pepsin cleave an Ig into?
- one F(ab')2 molecule
- Fc fragment degraded into smaller peptides)
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
Significance of the reducing agent studies that dissolved all the disulfide bonds?
established the existence of 2 heavy (H) and 2 light (L) chains in the Ig molecule
What two parts of the Ig form the pocket that binds an antigenic epitope?
VL and VH
What binds complement and mediates ADCC?
Fc portion of IgG (CH2 and CH3)
Which Ig's have a CH4 domain?
IgE and IgM
What do hinge regions do and what are they made of?
Provide flexibility, contain proline and cystines
What region of the Ig is glycosylated?
CH domains
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
What are the five flavors of Ig's/types of heavy chains?
M, G, A, D, E
Which Ig's lack a hinge region?
IgM and IgE
Which Ig contains a J chain?

Which Ig contains an SC segment?
- IgA and IgM

- IgA
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
Characteristics of IgG
- long half life
- secreted during late primary or early secondary response
- activates complement
- opsonizing antibody
- neutralizes toxins and viruses
Characteristics of IgM
- first Ig to appear during ontogeny and during immune response
- most effective complement activator
- natural isohemagglutinin (anti-AB)
Characteristics of IgD
- second receptor on B cell surface
- sensitive to proteolysis
- respiratory mucosa
- binds to mast cells an basophils
- triggers inflammatory burst releasing IL-1, TNF
Characteristics of IgE
- 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
Characteristics of IgA
- 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
Which Ig does NOT recruit inflammatory mediators, fix complement, or mediate ADCC?
What does the secretory component do? (2)
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
What is the major congenital immunodeficiency in humans?
IgA deficiency

--> microbes can enter the body, not trapped at epithelia, local infections

(systemic infections are NOT a problem)
Describe the synthesis of IgA
- 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
How do the J chain and secretory component (SC) differ in where they are added to the IgA dimmer?
J-chain: plasma cell

SC: epithelial cell
What do FcRns and FcRps do?
control levels of IgG, located on endothelial cells lining blood vessels
Describe IgG processing:
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
Difference between isotypes, allotypes, idiotypes
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)
Characteristics of TCRs
- remains on the surface of the cell
- kill infected cells (CTLs)
- produce cytokines
- see processed Ag in grooves of MHC, never free antigens
How does the C terminal of TCR differ from BCR?
TCR C-terminal does NOT extend into the cytosol of the cell

- relies on a series of other molecules to signal (CD3, 2 pairs)
Where as aB vs. yG TCRs expressed?
aB: throughout body (conventional and NKT cells)

yG: skin, mucosa, gut
What is another presenting molecule other than MHC that T-cells can recognize?
CD1 molecules that present lipid
SCID: genetic mutation?
ZAP-70, CD3, Rag
DiGeorge: genetic mutation?
22q11, 10p