Antigen

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Antigen
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Contents
? Foreignness and specificity of antigen ?
Factors that influence immunogenicity ?
Classification of antigen ? Nonspecific stimuli
for immune response
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?Basic conceptions 1 Antigen Any molecule that
can be specifically recognized by the adaptive
elements of the immune system, that is by B cells
or T cells, or both . 2 Immunogenicity Immunogeni
city is the ability to induce a humoral and/or
cell mediated immune response. 3 Antigenicity
(Reactogencity) Antigenicity is the ability to
combine specifically with the final products of
the above responses (i.e.,antibodies and/or
cell-surface receptors). 4 Complete antigen,
Immunogen Substance own both ability above.
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5 Hapten small organic molecules that have
antigenicity but immunogenicity . 6 Carrier a
large protein which chemical couples with a
hapten to yield an immunogenic hapten carrier
conjugate . 7 Epitope (antigenic determinant)
Epitopes are the immunological active regions of
an immunogen, which bind to antigen-specific
membrane receptors on lymphocytes or to secreted
antibodies. 8 antigenic valence Total number of
antigenic determinants of an antigen molecule,
which can specifically bind with their antibody.
9 Tolerogen, allergen
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? basic property of antigen 1 Foreignness Non-self
, changed selfe-antigen, antigens not exposed to
immature lymphocytes during embryonic period, all
of which posses immunogenicity 2 Specificity 1)
Type, character, number and steric configuration
of antigen epitope Contribution of properties of
chemical group to immunogenicity of
antigen Contribution of position of chemical
group to immunogenicity of antigen
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Contribution of position of chemical group (COOH)
to immunogenicity of hapten
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2) common epitope The epitope owned by different
antigens is called common epitope. cross reaction
Phenomenon that antibody can bind with different
antigens owned identical or alike epitope.
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Cross-reaction between BSA and albumin from
other genera
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3)epitope elementary structure and functional
unit of antigen molecule conformational/sequentia
l, discontinuous/linear, functional/cryptical
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Comparison of antigen recognized by T cells and B
cells
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? Factors influence immunogenicity of antigen 1
chemical and physical property of antigen
chemical property, molecular weight,
architecture, stability, Molecular conformation,
accessibility physical property 2 factor
from the recipient genotype, age, gender,
health 3 immunization methoddosage, route,
frequency, adjuvant
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chemical and physical property of antigen
immunogenicityheterogen, architectonic diversity
and molecular weight
proteantigen Polycose and lipoids antigen
Response type Cell immunity, humor immunity Humor immunity
Antibody type IgM,IgG and IgA et al IgM and little IgG
affinity high low
immunologic memory yes no
Inducibility of immune tolerance Not easy easy
physical properties
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• Antigenic Dosage
• Macro or micro -tolerance/medial-response
• Low-zone tolerance and high-zone tolerance
• the presence or absence of adjuvant
• The route of administration
• tolerationintravenous injectiongtintraperitoneal
  injection gt subcutaneouly injection and musc.
  injection
• Detention time of antigen in vivo
• Competitive inhibition between antigens
  antigen with resemble construction

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? classification of antigen complete antigen and
hapten complete antigenantigens with both
immunogenicity and antigenicity haptenantigens
with antigenicity but immunogenicity thymus
dependent antigen and thymus independent
antigen Thymus dependent antigen, TD-Ag Require
accession of T and APC to active B cell initial
both humor and cell immunity induce many types
of antibody induce immune memory
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Thymus independent antigen, TI-Ag Directly active
B cell independent T cell Only initial humor
immunity and induce IgM not induce immune
memory Comprise TI-1 and TI-2 Ag
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TD antigen TI-1 antigen TI-2 antigen
chemical property protein lipin polysaccharides Polysaccharides, glycans
Epitope type T, B epitope reduplicative B epitope bulk reduplicative B epitope
B cell clone activated Most B2 Mature and immature B1,B2 Mature B1
Neogenesis mouse and baby respond respond Non respond
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heterophile antigen, xenogenic antigen, allogenic
antigen, autoantigen, idiaotype
antigen heterophile antigen Common antigen owned
by different germ lines Forssma was the first to
find that there were common antigen between cony
pig organ and sheep erythrocytes , which was
called Forssman antigen. xenogenic
antigen Antigens from other species. allogenic
antigen Antigens from different individuals of
identical species
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autoantigen Self antigens under the some
conditions such as infection, trauma, drug
treatment and so on get antigenicity and induce
immune response. idiaotype antigen TCR?BCR or Ig
V can induce antibody production too.
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antibody
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? characteristics of interaction between antigen
and antibody 1 key to-lock- like spatial
configuration 2 non-covalent bond hydrogen
bonds, electrostatic interacton, van der waals
forces and hydrophobic force 3 reversible the
interaction can be impacted by temperature,
isoionic point, ionic strength and ratio of
antigen to antibody. 4 Affinity and Avidity 5
cross reaction
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? Superantigen, SAg 1 conceptionExceed low
dose(110ng/ml) of superantigen is needed to
active 220 of T cell clones to initiate very
strong immune response. 2 categoryExogenous
superantigen eg.Staphylococcus aureus enterotoxin
A-E Endogenous superantigen
eg. mouse mammary tumor virus protein 3
difference with common antigen 1)low dose, but
strong response 2)not constraint by
MHC 3)recognition is not specific,and procession
and presentation is not required 4)induce a lot
of cytokines releasing, resulting in severe
pathologic disease
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? Mitogens Substances which can active a cluster
of lymphocytes including a lot of clones. Such
as ConA, PHA,PWM, LPS and so on.
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? adjuvant 1 conception Adjuvants (from Latin
adjuvare, to help) are substances that, when
mixed with an antigen and injected with it,
enhance the immunogenicity of that antigen. 2
category Biological agents BCG Inorganic
compoundAl(OH)3 Synthesis cytidine
monophosphate(CMP),liposome immunostimulating
complex(ISCOM) CpG et al which is neotype of
adjuvant Freunds complete adjuvant (CFA) and
Freunds non-complete adjuvant (IFA) are commonly
used 3 mechanism of action n Prolong antigen
persistence n Enhance co-stimulatory signals n
Induce granuloma formation n Stimulate lymphocyte
proliferation nonspecifically
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• Master conception and basic characteristics
• Master the definition of hapten, immunogen and
  epitope
• Master factors that influence immunogenicity of
  antigen
• Master the conception of TD-Ag and TI-Ag and the
  distinction between the two
• Master the distinction between T-cell epitope and
  B-cell epitope and the relationgship between them
  and TD-Ag
• Be familiar with cross-reaction and heterophile
  antigen and their clinic meaning
• Understand classification of antigen
• Understand conception and classification of
  superantigen