Assignment #12 Flashcards
what is the basic structure of monomeric antibody?
two identical light chains covalently linked to two identical heavy chains. Each chain has a variable region and constant region
What are three forms other than monomeric?
dimeric, trimeric and pentameric forms
What are 5 antibody isotypes?
IgA, IgD, IgE, IgG and IgM with 5 different heavy chain constant regions named Greek letters alpha (α), delta (δ), epsilon (ε), gamma (γ) or mu (μ)
In general terms what does the term subclass mean as it relates to IgG and IgA?
Antibodies with small differences in AA sequence in heavy chain constant region, unique properties (IgG1, IgG2, IgG3, IgG4, and IgA1, IgA2)
subclass - variations within an individual
In general terms define the term allotype as it relates to IgG and IgA?
polymorphism with a IgG or IgA constant region
Gm and Am respectively
allotype - variations between individuals
What is meant by bifunctional molecule, in regards to an antibody?
posses both an antigen-binding capacity and a biological activity region
what is meant by biological activity in regards to an antibody?
biological activity in the constant region confers different roles for isotypes.
what is meant by specificity in regards to antibodies?
refers to antigen recognition and binding
What are three names for sites within the variable region that bind the epitope?
Hypervariable region, complementary determining region (CDR), and paratope
Define the term affinity, in regards to antigen-antibody interaction
The strength of the interaction between one antigen binding site and its monovalent antigen. (hydrophobic and ionic)
Define the term avidity in terms of antigen antibody interaction
describes the overall binding energy of all antigen-binding sites with antigen
Properties of IgG
150kd monomer
75% of the total circulating (highest in circulation)
four subclasses with different biological activities (IgG1, IgG2, IgG3, and IgG4)
20 allotypes (Gm) polymorphisms
Half life about 3 weeks (LONGEST)
All IgGs cross the placenta
Receptors for Fcgamma on monocytes, macrophages, neutrophils and B cells
Roles of IgG
Down regulation of B cells following binding to antigen and Fcgamma R
Elimination of microbes by facilitating: opsonization by phagocytes
antibody-dependent cell mediated cytotoxicity (ADCC) by NK cells
neutralization of viruses and toxins
complement activation
Properties of IgM
Exists as a monomer on B cells
Pentamer when secreted from plasma cells
15% of total circulating immunoglobulins
Half life 5-7 days
Pentameric form: five covalently attached monomeric units and short J chain and has ten antigen binding sites
Only antibody isotype present on immature B cells
Role of IgM
Activate classical pathway of complement (most efficient when bound to antigen)
only one IgM antigen/antigen complex required to activate classical pathway
IgM iso-hemagglutinins responsibile for ABO blood system
Properties and Role of IgD
Exists primarily as a membrane bound monomeric form
expressed on naive mature B cells along with IgM
Low detectable serum levels of IgD
Properties and Role of IgE
monomeric antibody
normal barely detectable in serum
multivalent antigen bound to IgE results in crosslinking of FceRs
Cross linking= release of inflammatory mediators from preformed granules present in mast cells and basophils
Properties of IgA
Exists as a monomer, dimer or a trimer J chain on dimers and trimers IgA half life of one week subclasses: IgA1 and IgA 2 Allotypes: Am transferred to infants during feeding activates alternative complement pathway
Mechansim of IgA in intestinal lumen
B cells activated in lamina propria –> plasma cells
plasma cells secrete dimeric IgA (D-IgA)
D-IgA binds to secretory component (SC) on epithelial cells
D-IgA attached to SC transported in vesicle through epithelial cell (E-cells)
At lumenal side of E cells, SC cleaved; D-IgA retains a piece= D-IgA-SC
SC protects D-IgA-SC from degradation; D-IgA-SC is referred to as secretory IgA
Overall role of IgA in the intestinal lumen
Binds to and neutralizes pathogens
Binds to microbes before they bind to M cells
So where are the secretory vs dimeric IgA located???
Secretory IgA —> Lumen
Dimeric IgA —> lamina propria
Type O, cell surface antigen? antibody isohemagglutinin? and who can they receive blood from?
Cell Surface Antigen –> None
Antibody Isohemmagglutinin —> Anti A and Anti B
Receive blood from individuals who are type O
Type A, cell surface antigen? antibody isohemagglutinin? and who can they receive blood from?
Cell surface antigen –> A antigens
Antibodies Isohemagglutinin –> Anti B
Receive blood from individuals who are–> Type A
Type B, cell surface antigen? antibody isohemagglutinin?and who can they receive blood from?
Cell surface antigen –> b antigens
antibodies isohemagglutini –> anti A
receive blood from individuals who are–> type B
