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antigen
variety of “large” molecular structures that can interact with an antibody/T cell receptor
triggers immune system to start producing antibodies
immunogens
antigens that are recognized by a person’s immune system as foreign, causing response
not all antigens are immunogens
tolerogens
antigens that an individual has already developed a tolerance for — no immune response
allergens
type of antigen that produces abnormally vigorous immune response against threat that is usually harmless to body
response from IgE antibodies — stimulate mast cells
antigenicity/immunogenicity
potency/extent to which the antigen induces immune response
hapten
chemically active substance of low molecular weight
unable to induce immune response by itself, but immunogenic when conjugated with carrier molecule
heterophile antibodies
endogenous antibodies present in serum/plasma that may interfere w immunoassays
heterophile antigens
antigen common to more than one species
the ab produced due to exposure to the human ag will also react with an ag from an unrelated species
epitope
aka antigenic determinant
component on antigen that reacts with antibody — lock and key
carrier regions
regions on antigen structure to which antibody is not formed — not recognized as foreign, therefore wbcs dont make antibody for the region
specificity
exact atomic and molecular characteristics of epitope that enables it to be recognized and classified
factors affecting immunogenicity
chemical nature of antigens
chemical complexity
molecular size
structural conformation of molecule
ionic charge
foreignness
route, dosage and frequency of exposure to immunogen
genetic composition of host
adjuvants
how does the chemical nature of antigens affect immunogenicity
best antigens: proteins — synthesize IgG
polysaccharides (carbs) less immunogenic — synthesize IgM
lipids not immunogenic in pure form, can become immunogenic when bound to carrier protein
nucleic acids not immunogenic, can be if bonded to proteins
inorganic substances dont activate lymphocytes to produce Abs
how does the chemical complexity of antigens affect immunogenicity
more complex, immunogenicity increases
how does the molecular size of antigens affect immunogenicity
large molecules better at eliciting immune response than small
how does the structural conformation of antigens affect immunogenicity
change in 3d orientation of molecule by chemical/thermal denaturation changes accessibility of epitopes
more accessible epitopes, more antigenic it is
how does the ionic charge of antigens affect immunogenicity
molecules dont have to be charged to be antigenic
higher charge might decrease immunogenicity bcs repulsion
how does the foreignness of antigens affect immunogenicity
how different the antigen is from our “self” antigens
how does the route of antigens affect immunogenicity
three routes:
blood > spleen > encounters B lymphocytes — produce Abs
skin/subcutaneous tissue > macrophages arrive > carried to lymphatic system > lymph nodes > exposure to B lymphs
GI or resp tracts > special lymphoid organs trap antigen > process
if antigens are destroyed through innate immune responses, will not initiate adaptive immune response
how does the dosage/frequency of exposure to antigens affect immunogenicity
exposure to higher dosage usually increases immunogenicity
repeated exposure might increase it as well
how does the genetic composition of the host affect immunogenicity
major histocompatibility complex MHC genes control immune responsiveness to antigens
very young and very old have weaker immune systems
immunocompromised individuals are more susceptible to antigens
how do adjuvants affect immunogenicity
agents that non-specifically enhance immune response when administered with antigen
not immunogenic and cannot evoke response on own
what produces antibodies
b-lymphocytes
how are antibodies secreted and in what forms
through exocytosis
membrane bound and secreted form
membrane bound antibodies
serve as B cell antigen receptor
make contact with specific antigen, B cell differentiates into plasma cell
plasma cells
produce antibodies
differentiated from B cells
secreted form antibodies
plasma cells secrete free antibody into blood/lymph
promotes phagocytosis, neutralize antigens, activates complements
what bonds link the chains in an antibody
disulphide bonds
types of light chains
kappa and lambda
types of heavy chains
gamma, alpha, mu, epsilon, delta
basic monomeric unit
makes up antibodies
composed of 4 polypeptide chains — 2 heavy, 2 light
domains
loops of ~110 amino acids on light/heavy chains of antibodies
variable domains
amino acid sequences specific to epitope of antigen
specificity and binding site
function of constant light chain
determines if chain is kappa or lambda
orientates antibody during antigen binding
function of variable light chain
determines antibody specificity
site of antigen binding
function of variable heavy chain
determines antibody specificity
site of antigen binding
function of constant heavy chain 1
orientates antibody during antigen binding
function of constant heavy chain 2
involved in complement activation
function of constant heavy chain 3
involved in phagocyte binding
what joins together monomeric units in non-monomers
J chain
Fab fragment
fragment, antigen binding
consists of entire light chain and half of heavy chain
amine end of antibody
site that recognizes and binds to antigen (epitope)
Fc fragment
fragment, crystalline
other half of heavy chain
carboxyl end of antibody
amino acid sequence is identical to all antibodies of the class/subclass
functions of Fc fragment
complement activation
macrophages have receptors for CH3 of IgG — phagocytosis
transport of igG molecules across placenta into baby
ingested IgA from mother’s milk transported across gut epithelium
isotypes
different classes and subclasses of antibodies
classified according to heavy chains they contain
IgG IgA IgM IgE IgD (classes)
IgG1 IgG2 IgG3 IgG4 (subclasses)
differ from species to species
allotypes
structural differences in constant region of chains within class of antibody
inherited
idiotype
unique amino acid sequences (idiotopes) found in variable domain of chains
most abundant antibody class in serum
IgG: 70-80%
IgG
gamma chains, monomer; two binding sites
70-80% of total Ab
crosses placenta
functions:
opsonization
activates complement
neonate and long term immunity
memory antibodies
IgM
mu chains, pentamer; ten binding sites
10% of total Abs
functions:
first Ab produced in immune response
first Ab produced by newborn
activates complement
IgE
epsilon chains, monomer; two binding sites
<1% of total Abs
functions:
allergy Ab
parasitic infections
IgA
alpha chains, dimer; four binding sites (also exists as monomer)
connected by J chains
15% of total Abs
functions:
mucosal immunity
saliva, skin (sweat), mucosal lining (GI)
passive Ab to baby through breast milk
IgD
delta chains, monomer; two binding sites
0.2% of total Abs
functions:
naive B cell antigen for Ag recognition
where does a newborn get its immunity
IgG from mother through placenta
IgA from breastmilk
what happens to newborn’s immunity over first six months
maternal IgG levels decline, baby begins producing own immunoglobulin synthesis
when does IgM synthesis begin in newborns
three months before birth
when does IgG synthesis begin in newborns
three to six weeks after birth
Abs first detectable at two months
when does IgA synthesis occur in newborns
three months
meconium
dark green substance on intestine in full term infants
consists of intestinal gland secretions and amniotic fluid
contains IgG
colostrum
thin milky fluid of mammary gland produced few days before/after birth
contains IgA