MOD2 Antigens and Antibodies

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59 Terms

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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

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immunogens

antigens that are recognized by a person’s immune system as foreign, causing response

not all antigens are immunogens

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tolerogens

antigens that an individual has already developed a tolerance for — no immune response

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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 

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antigenicity/immunogenicity

potency/extent to which the antigen induces immune response

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hapten

chemically active substance of low molecular weight

unable to induce immune response by itself, but immunogenic when conjugated with carrier molecule

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heterophile antibodies 

endogenous antibodies present in serum/plasma that may interfere w immunoassays

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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 

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epitope

aka antigenic determinant

component on antigen that reacts with antibody — lock and key

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carrier regions

regions on antigen structure to which antibody is not formed — not recognized as foreign, therefore wbcs dont make antibody for the region

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specificity 

exact atomic and molecular characteristics of epitope that enables it to be recognized and classified 

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factors affecting immunogenicity

  1. chemical nature of antigens

  2. chemical complexity

  3. molecular size

  4. structural conformation of molecule

  5. ionic charge

  6. foreignness

  7. route, dosage and frequency of exposure to immunogen

  8. genetic composition of host

  9. adjuvants

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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

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how does the chemical complexity of antigens affect immunogenicity

more complex, immunogenicity increases

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how does the molecular size of antigens affect immunogenicity

large molecules better at eliciting immune response than small

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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

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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

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how does the foreignness of antigens affect immunogenicity

how different the antigen is from our “self” antigens 

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how does the route of antigens affect immunogenicity

three routes:

  1. blood > spleen > encounters B lymphocytes — produce Abs

  2. skin/subcutaneous tissue > macrophages arrive > carried to lymphatic system > lymph nodes > exposure to B lymphs

  3. GI or resp tracts > special lymphoid organs trap antigen > process

if antigens are destroyed through innate immune responses, will not initiate adaptive immune response

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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 

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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 

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how do adjuvants affect immunogenicity

agents that non-specifically enhance immune response when administered with antigen

not immunogenic and cannot evoke response on own

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what produces antibodies

b-lymphocytes

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how are antibodies secreted and in what forms 

through exocytosis 

membrane bound and secreted form

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membrane bound antibodies

serve as B cell antigen receptor

make contact with specific antigen, B cell differentiates into plasma cell

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plasma cells

produce antibodies

differentiated from B cells

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secreted form antibodies 

plasma cells secrete free antibody into blood/lymph

promotes phagocytosis, neutralize antigens, activates complements 

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what bonds link the chains in an antibody

disulphide bonds 

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types of light chains

kappa and lambda

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types of heavy chains

gamma, alpha, mu, epsilon, delta

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basic monomeric unit 

makes up antibodies 

composed of 4 polypeptide chains — 2 heavy, 2 light 

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domains

loops of ~110 amino acids on light/heavy chains of antibodies

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variable domains

amino acid sequences specific to epitope of antigen

specificity and binding site

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function of constant light chain

determines if chain is kappa or lambda

orientates antibody during antigen binding

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function of variable light chain

determines antibody specificity

site of antigen binding

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function of variable heavy chain

determines antibody specificity

site of antigen binding

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function of constant heavy chain 1

orientates antibody during antigen binding

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function of constant heavy chain 2

involved in complement activation

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function of constant heavy chain 3

involved in phagocyte binding

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what joins together monomeric units in non-monomers 

J chain 

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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)

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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

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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

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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

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allotypes

structural differences in constant region of chains within class of antibody

inherited

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idiotype 

unique amino acid sequences (idiotopes) found in variable domain of chains 

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most abundant antibody class in serum

IgG: 70-80%

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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 

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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

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IgE

epsilon chains, monomer; two binding sites

<1% of total Abs 

functions:

  • allergy Ab 

  • parasitic infections 

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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

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IgD

delta chains, monomer; two binding sites 

0.2% of total Abs

functions: 

  • naive B cell antigen for Ag recognition 

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where does a newborn get its immunity

IgG from mother through placenta

IgA from breastmilk

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what happens to newborn’s immunity over first six months 

maternal IgG levels decline, baby begins producing own immunoglobulin synthesis 

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when does IgM synthesis begin in newborns

three months before birth

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when does IgG synthesis begin in newborns

three to six weeks after birth

Abs first detectable at two months

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when does IgA synthesis occur in newborns 

three months 

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meconium

dark green substance on intestine in full term infants

consists of intestinal gland secretions and amniotic fluid

contains IgG

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colostrum

thin milky fluid of mammary gland produced few days before/after birth

contains IgA