immunoglobulins Flashcards
what is another name for immunoglobulins
antibodies
what do antibodies do
they recognise antigens
what is an antigen
any substance which elicits an immune response
portion recognised =?
epitope or antigenic determinant
where are antibodies present
plasma, tissues, secretions and lymphatic system
what are the 5 classes of immunoglobulins
IgG
IgM
IgA
IgD
IgE
they provide recognition function and trigger effector functions
what bond holds immunoglobulins together
disulphide bridges
what is Fab
Fragment antigen binding - responsible for binding antigen
what is Fc
Fragment crystallisable - responsible for effector function
what are the two types of light chains
Lamba and kappa
all antibody classes use these same light chains
in any individual antibody molecule both light chains are the same
what determines the class of antibodies
heavy chains
light chains fold up into how many globular domains
2
heavy chains fold up into how many globular domains
4 or 5
what is each domain comprised of and what links them
they are comprised of 2 beta sheets and are linked by disulphide bridges to form a beta barrel
what do n-linked oligosaccharides attach to
Asn residue in the sequence Asn-X-Ser/Thr where x is an amino acid except Pro
what does CDR stand for
complementary determining region
what happens when VH and VL domains are paired
their 6 CDRs lie close together and create the antigen-binding site
what do antibodies recognize
structural epitope on the antigen
antiboy binds antigens with various (blank) interactions
non-covalent
Electrostatic forces
Attraction between opposite charges e.g.NH3+ and COO-
Hydrogen bonds
Hydrogen shared between electronegative atoms (N, O)
Van der Waals forces
Fluctuations in electron clouds around molecules oppositely polarise neighboring atoms
Hydrophobic forces
Hydrophobic groups interact unfavourablywith water and tend to pack together toexclude water molecules. The attractionalso involves Van der Waals forces
explain and describe IgG
- Most abundant Ig in plasma (10 mg/ml)
- Y shaped2 HC of 50 kDa mass, 2 LC of 25 kDa mass4 subclasses - IgG1, IgG2, IgG3, IgG4
- Very efficient at triggering complement and phagocytosis via Fc receptors
- Only Ig class to cross the placenta from mother to fetus - protects baby in first months of life
- Predominant antibody of 2o response
explain and describe IgM
- Only in plasma and secretions - too large to enter tissues
- Pentamer - 5 Y-shaped units joined by Joining (J) chain and disulfide bridgesHeavy chain has 5 globular domains
- Very efficient at activating complement
- Ten binding sites for antigen - very good agglutinating particles e.g. viruses
- Predominant antibody of 1o response
explain and describe IgA
Important serum Ig (2-3 mg/ml)
Major antibodies in seromucous secretions.g. saliva, milk, colostrum gut, tracheobronchial system genito-urinary system
Class of antibody first encountered by many invading bacteria and viruses
1. Two subclasses - IgA1, IgA2
2. Monomeric and dimeric forms
3. Serum IgA – monomeric90% IgA1, 10% IgA2
4. Secretory IgA - predominantly dimeric40% IgA1, 60% IgA2Additional polypeptide (secretory component SC)derived from receptor mediating export to secretions
5. SC protects in the harsh environments of secretions
IgE function
Associated with an allergic response
Important for protection against parasitic infections
IgD
Very low serum concentrations
Found on the surface of lymphocytes
Function unclear - may be involved in the control of antibody response
Recently implicated in mucosal immunity
Neutralizing antibodies=
IgG and IgA are efficient at binding to soluble toxins preventing them from binding to cell surface receptors
what do allergic individuals make
IgE responses to innocuous antigens (allergens)FcRI is cross-linked —> release of inflammatory mediators like histamine
summary
Structure on antigen recognised by an antibody is termed the‘epitope’ or ‘antigenic determinant’
Antibodies fold into globular domains with distinctive 3D structure
Hypervariable regions (CDR) in variable domains govern antigenbinding
Three-dimensional complementarity of structures of antigen binding site and antigen lead to high specificity and affinity
Different Ig isotypes are expressed at different body sites and have different functions
Antibodies act as flexible adaptors, linking antigen recognition to elimination mechanisms
Key functions of antibodies are blocking, neutralization, complement activation and cell activation through Fc receptor
