Antigens, Antibodies and Interactions Flashcards
Antibody
soluble/membrane bound glycoprotein that recognize and bind antigens. Through the receptor binding of the constant region cause a variety of responses that aid in immune response and clearance of pathogen.
hypervariable region
regions within the variable regions of both light and heavy chains of antibody that shows exceptional variability and are intimately involved in antigen binding by creating an interaction site that is complementary in shape, charge and hydrophobicity to the epitope
- also known as complementarity determining regions (CDR) or idiotype
isotype
Determined by the C region of the heavy chain defining the class, structural and functional differences of antibody. There are 9 classes (including subclasses) in humans
Describe the various isotypes of antibodies present in humans.
IgM - first antibody produced during the primary immune response (also produced by neonates); pentamer in serum (efficient at C’)
IgG - most abundant class in serum (monomer) and is split into 4 subclasses with different functions.
- 1, 2, 3, 4, can all cross the placenta
- 1, 3 bind Fc receptor on phagocytes w/ high affinity (4 intermediate)
- 2 is restricted to carbohydrates
IgA - mucosal immunity, secreted as dimer that can cross
IgE - present in allergies, binds to Fc receptor of mast cells and basophils
IgD - no real function, not secreted and only present on membrane
antigen
foreign molecules that bind to an antibody or TCR whether or not they induce an immune response
immunogens
antigens that induce an immune response (all immunogens are antigens, not all antigens are immunogens)
epitope
specific part of antigen that contact the Ag-binding sites of Ab or TCR (antigenic determinate)
pathogen
an organism that causes disease
haptens
small molecular weight molecules that can bind to an antibody but must be attached to a large carrier macromolecule to stimulate an immune response specific for the small molecule
Describe the difference between endogenous antigens and exogenous antigens
endogenous antigen - body’s own cellular components or intracellular pathogens (autoantigens, alloantigens, intracellular pathogens)
exogenous antigen - antigens that enter the body or system and freely circulate in the body fluids to be trapped and presented by APC through phagocytosis (allergens, iatrogens, microbial)
What factors influence immunogenicity?
molecular mass, foreignness, chemical composition, physical form, degradability, genetic factors, age
when it comes to vaccinations: dose, route, and use of adjuvants.
Describe the differences between the epitopes recognized by B cells and that recognized by T cells.
B cell recognition - epitopes are 3D, hydrophilic sequential or non sequential amino acids that are easily accessible. It is the conformation that matters. Will also recognize polysaccharides and lipids
T cell recognition - epitopes are primary sequences of amino acids (8-15 aa) presented in MHC
What is the difference between T-dependent and T-independent Ags?
T-dependent antigens require both Th cells and B cells to simulate and immune response (proteins)
T-independent antigens can stimulate antibody response w/o the help of T cells (polysaccharides and lipids, usually multiple identical epitopes that cross-link BCR)
define superantigen
superantigen - protein secreted by bacteria which activates T cells nonspecifically by binding to the V-beta chain of TCR w/o need of antigen. Causes suppression of the immune system through hyperactivation and the cytokine storm induced
- staphylococcal enterotoxins (food poisoning)
- staphylococcal toxic shock toxin (TSS)
- staphylococcal exfoliating toxins (scalded skin syndrome)
- streptococcal pyrogenic exotoxin (shock)
How does antigen bind to antibody? Define affinity and avidity.
noncovalent bonding
affinity - strength of interaction between single epitope and idiotope
avidity - combined strength of interaction of many antibodies to one antigen
