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48 Cards in this Set
- Front
- Back
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Immunoglobulin
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= Ig = Antibody = Ab = gamma globulins
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the ___________ of a B cell is due to the membrane bound Ig (part of the BCR complex)
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Ag specificity
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Abs can bind a variety of antigens
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Proteins, polysaccarides, lipids, nucleic acids
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Clonal selection and proliferation happens when
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B cell recognizes it’s antigen and multiplies
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Once a B cell is activated it differentiates into a memory cell or _______ which produces Ab with ____ antigenetic specificity.
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plasma cell (effector cell);ONE
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Overview of Ig functions
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-Pathogen neutralization
-Complement (C’) fixation -Antibody-dependent cellular cytotoxicity (ADCC) -Opsonization -Inflammation |
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agglutinatization
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Ab can cause clumping together of cell
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Precipitation
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Ab can cause clumping together of small molecules
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multiple myelomas
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cancer of a B cell producing a monoclonal Ig
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Heavy chain variation
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mu,gamma,alpha,delta, or epsilon
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light chain variations
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kappa, lambda
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antigen binding takes place on the ________ region of B cell Ag
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variable region
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Biological activity takes place on the ________ region of B cell Ag
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Biological activity region
-where carbohydrate portions interact with complement |
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Ab structure
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2 identical heavy chains and 2 identical light chains
-H-chains joined together by disulfide bonds in the hinge region -L-chains joined to H chains by a disulfide bond in the CL region -5 classes of heavy chains (isotypes: IgG, IgM, IgA, IgE, and IgD…a/k/a g, m, a, e, and d) -2 types of light chains (k or l) -Both H and L chains have intrachain disulfide bonds -Ab binds in the N-terminal end where the VL and VH are joined -F(ab) binds Ag -Fc has biologic activity (C’ activation, ADCC) |
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F(ab)=
Fc = |
-binds Ag
-has biologic activity (C’ activation, ADCC) |
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Ab has both ______ and _______ in its constant region and only _______ in its variable region
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intrachain disulfide bonds, interchain disulfide bonds, intrachain disulfide bonds
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intra chain immunoglobin fold
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coded for by IG gene superfamily, connected by intrachain disulfide bond
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IG subtypes with additional domains in constant region
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mu, epsilon
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________ of heavy chain determines function
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glycosilation
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Ig domain/fold
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-The Ab molecule is made up of Ig domains
-Each domain is ~100-110a.a. long -Contains an intrachain disulfide bond -Molecules with this fold are members of the Ig gene superfamily |
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Ag binding domain
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N-terminal region of variable region of heavy and light chain binds to Ag
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Variability is concentrated in three regions:
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Hypervariable regions
Called Complementarity determining regions (CDR): CDR1, CDR2, and CDR3 -CDR3 makes most of the contact with Ag -Framework regions – areas of variable region that are less variable |
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Fab
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antigen binding (VH:VL)
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Fc
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biological activity
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5 H chain isotypes
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m, g, d, a, and e
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4 IgG
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g1, g2, g3, and g4
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2 IgA
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a1 and a2
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2 L chain types
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k and l
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Each Ab has 2 ______ H and 2 _______ L chains
In humans: __ of Ig have k, ___ have l |
identical/ identical
60%/40% |
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five different IGs have different amounts of ____
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glycosolation
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Monomer-bivalent isotypes
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IgG,IgE,IgD
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dimer- multivalent isotype
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IgA,
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pentamer-multivalent isotype
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IgM
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J-chain (joining)
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holds multimers together
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Ig distribution in plasma
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IgG (highest cuz involved in secondary immune response) and IgM; very low IgA, IgD and IgE
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Ig distribution in tissue fluids
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IgG, some IgM and some IgA monomers
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Ig distribution in secretions
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secretory IgA (dimers); small amounts of IgG in MALT
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Ig distribution Fetus
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passive IgG from mom (IgG1, IgG3, IgG4)
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Ig distribution Beneath epithelium
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IgE on mast cells
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Ig distribution Brain
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none unless damage to blood brain barrier
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IgM
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-pentameric when secreted from plasma cell
-10 Ag binding sites (highest valence of Igs) -monomer on surface of mature B cell -joined together by J-chain (15,000 mw) -appears first during the primary immune response best at C’ activation because need two Fc regions close together -best agglutinating Ab – best at clumping together cells |
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IgG
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-always a monomer
-2 Ag binding sites -4 subclasses -predominant Ig in blood and lymph -Longest half life of isotypes (23 days vs. 2-5 days) -appears in late primary and early secondary immune response -can activate C’ -some subclasses cross the placenta -Opsonin ( can bind to cells and act as a signal) and mediates ADCC( Ab dependant cellular cyttoxicity) |
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IgA
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Secretory Ig
-monomer on surface of B cell -dimer (can be tetramer) when in secretions -J chain holds Ig together -Secretory component (SC) present -protective protein -SC ~70,000 mw -mucophilic – attaches to epithelial and traps Ags in mucous where lysozyme can help degrade -Two subclasses -Major Ig in the body (highest concentration) vs igg in blood |
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IgD
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-monomer
-second receptor on B cell (after IgM) -co-expressed on surface of B cell -unknown function -Initial B cell activation?? |
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IgE
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-reagin – binds to basophils and mast cells
-lowest concentration in the serum -cleared from serum when binding to mast cells -short half-life in blood but long on surface of mast cell -when binds Ag, causes degranulation of mast cell = allergic reaction -a/k/a Type I hypersensitivity (Immediate type hypersensitivity) -protection against parasitic worms – causes acute inflammatory reaction |
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Isotypes
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-classes of Igs (5 major classes in humans)
-determined by C-regions of the H-chain -some describe light chain isotypes as well (k and l) |
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Allotypes
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allelic forms of the same protein that can vary WITHIN A SPECIES (my Ab & your Ab)
usually 1-2 a.a. changes |
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Idiotypes
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– due to the variable region of the Ig (differences in a.a. sequences due to variable binding to Ags) – determines Ag speficity
essentially a clonal marker for a given B cell |
