59-Antibody Structure and Function Flashcards
antigen receptors
on surface of lymphocytes
B cell receptors
T cell receptors
many different receptors to recognize unlimited number of foreign Ags
clonically expressed-1 unique Ag receptor per lymphocyte clone
Surface BCR and soluble Ab molecules
identical except small transmembrane sequence on C terminal end
function of BCR
recognition of antigen
initiates signal transduction using CD79a/b to start intracellular signaling
CD79
needed for BCR to start intracellular signalling
structure of Ab
2 heavy chains
2 light chains
hinge region for torsion
disulfide bonds to hold molecules together
N linked carb chains linked to heavy chain for 3D structure and half life
variable region
heavy-VDJ
light-VJ
form antigen binding pocket, 2 identical pockets that bind identical antigens
constant region
no recombination, ensure structural integrity
H chain is for key effector functions
Fab region
Ag binding, 2 Fab regions=Fab2, bind 2 identical antigens
Fc region
below hinge region, heavy chain constant region
effector functions
Fab
cleave above hinge
Fc
cleave above hinge
Fab2
cleave below hinge
hypervariability regions
3 regions in both heavy and light, “complementarity determining regions”
1 and 2 and encoded in DNA
3 is recombination of VDJ or VJ
CDR
complementarity determining regions, variability in heavy and light chains
proximal in tertiary structure and form Ag binding pocket
epitope
small segment of Ag bound by Ag binding pocket, non covalent interactions
what can TCRs recognize vs BCR/Ag
TCR-peptides, require MHC
BCR/Ag-lipid, carb, protein, nucleic acid, interact with epitopes on surface of pathogens, do not require MHC
end product of B cell activation
cell that secretes Abs (soluble version of BCR) that recognize pathogen epitope and bind then recruite innate immunity to mediate destruction
Ab isotypes
defined by heavy chain constant region
5 isotopes encoded by loci
IgM, G, A, E, D
subclasses of Ab
IgG-4
IgA-2
IgM structure
4 constant regions, no hinge
large and inflexible=only in blood
secreted as pentamer-10 binding sites
antibody that is a pentamer
IgM
IgM functions
neutralization
agglutination
complement activation
neutralization Abs
IgM, IgG, IgA
agglutination Abs
IgM, IgG, IgA
complement activation Abs
IgM, IgG
IgG structure
3 constant regions with hinge
secreted as monomer-2 binding sites
most abundant
found in blood and tissues
antibody that is a monomer
IgG, IgA in blood, IgE
IgG functions
neutralization agglutiniation complement activation opsonization/phagocytosis Ab dependent cellular cytotoxicity transplacental transfer
opsonization/phagocytosis Abs
IgG, IgA
Ab dependent cellular cytotoxicity Abs
IgG
passive immunity to fetus through placenta Abs
IgG
IgA structure
3 constant regions with hinge
monomer in blood
dimer in mucosal secretions
antibody that is a dimer
IgA in mucosal secretions
IgA functions
neutralization
agglutination
opsonization/phagocytosis
immunity in breast milk
immunity in breast milk Abs
IgA
IgE structure
4 constant regions, no hinge region
monomer
IgE function
bound to mast cells with high affinity
mediate type 1 hypersensitivity reaction/ allergic reaction
allergic reaction Abs
IgE
IgD structure
3 constant regions with hinge, rarely secretes, used as BCR on naive B cells
no hinge
IgM, IgE
agglutination
traps microbes in a complex
impair movement, attachment, replication, colony formation
IgM, G, A- lots of binding sites or hinge with torsion
neutralization
prevent pathogens and toxins from binding to their host
IgM, G, A
Complement activation-Classical pathway
Ab binding to Ag makes immune complex formation
allosteric change in Fc to bind C1q to start complement cascade, Use IgM, G
recruit C4 and 2, activation of C3 convertase
cleave C3, C3a inflammation, C3b opsinization
recruit and cleave C5, C5a inflammation
C5b recruits C6, 7, 8, 9 to form MAC, create channel and lyse
Opsonization
coating of pathogen with ligand recognized by phagocytic cells
IgG, IgA, C3b
Phagocytic cell receptors
Fc receptor bind antibodies
C3b receptor bind C3b
4 IgG Fc receptors, 1 IgA Fc receptor, 4 C3b receptor
natural killer cells
IgG Fc receptors bind IgG Abs with their Fc tail
provide specifficity to NK cells to recognize and bind Ags on target cells
kill using proteolytic enzymes and inducing apoptosis
maternal IgG
to fetus through circulation
can cause disease
hemolytic disease of newborns
IgG aBs against Rh blood group, give RhoGAM to Rh- moms
maternal IgA
in mothers milk
protect baby’s gut
