Antibody Structure and Function Flashcards Preview

Microbiology/Immunology > Antibody Structure and Function > Flashcards

Flashcards in Antibody Structure and Function Deck (14)

General antibody release mechanism

-a resting B cell with membrane bound Ig
-it then has an encounter with antigen like on a bacterium
-the stimulated B cell gives rise to anti-body secreting plasma cells


General structure of the antibody

-It has a heavy chain, which is on the bottom and also internal on top
-the sides are held together by disulfide bonds
-the ends that bind antigen binding sites are the N-termini
-the antigen binding sites are the variable region, where the other parts are the constant region for that antibody type
-gamma globulin fraction contained most of the antibody


Use of antibodies

-neutralization- such as with toxins or viruses
-opsonization by itself or combined with complement which causes the pathogen to be ingested and degraded by phagocyte


Molecular weight and antibody type

IgGs -about 150 kDa
IgM- 970 kDa because there are multiple


Functions of antibodies

-Neutralization- IgGs and IgA, IgM-a little
-Opsonization- IgG1 and 3 and IGg 4 and IgGA a little
-Activate NK cells- IgG1 and 3
-Activate Mast cells- IgG1 and 3 a little, IgE a lot
-Activation of complement- IgM, IgGs, IgA a little
-Transport across epithelium- IgA, a little IgM
-transport across placenta- IgG


Mean serum level of antibody types

IgM- 1.5 (mg/ml)
IgD- 0.03
IgG1- 9
IgG2- 3
IgG3- 1
IgG4- 0.5
IgA- 2.5
IgE- 5 x 10^-5



-MW 150,000
-predominant class in serum
-toxin neutralizing, agglutinating, opsonizing, bacteriolytic (with aid of complement system)
-subclasses IgG1, IgG2, IgG3, IgG4
-intrachain disulfide bond occurs between the same residues


Phagocytosis via antibody use

-antibody binds to bacterium
-antibody coated bacterium binds to Fc receptors on cell surface
-macrophage membrane surrounds bacterium
-macrophage membranes fuse, creating a membrane-bounded vesicles, the phagosome
-lysosomes fuse with the phagosome, creating the phagolysosome


Immunoglobin M

-MW 900,000- because usually pentameric
-predominant class in primary immune response
-antigen receptor on B lymphocyte. With the aid of the complement system it can be opsonizing and bacteriolytic. It cannot aid in opsonization without complement as cells do not have FcM receptors
-5-10% of serum Igs
-4 heavy chain domains, no hinge region
-J chain (15,000 MW)



-MW 160,000- usually dimeric
-predominant class in secretions
-found in monomer, dimers, and trimers
-15% of serum Igs
-secretory piece (T piece)- resists acid hydrolysis
-J chain
-agglutinating, opsonizing



-MW 180,000
- located on the surface of human immature B-lymphocytes
-associated with some tumor cells
-0.2% of serum Igs
-co-expressed with IgM on surface of B- lymphocytes
-may function as an antigen receptor



-MW 200,000
-immediate hypersensitivity
-fixes to mast cells- antigen cross links IgE antibody bound at the mast-cell surface causing release of granule contents
-0.1% of serum Igs
-mediate changes in vascular permeability
-may be involved in host defense against parasitic infection


Proteolytic degradation of immunoglobins

-papain digests the hinge region
-one fragment can be crystalized- contain most of the IgG specific antigenic determinants and is called Fc
-other two regions can still bind antigen and are not crystalizable (more variabe)- Fab
-pepsin can make F(ab')2 fragments


Domains in antibodies

-light chain C domain- constant
-light chain V domain- variable
-also have three hypervariable regions- very specific antigen binding site