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Immune molecules
Section 3
Chapter 1
properties of antigen
immunogen
Any substance capable of inducing
an immune response.
Antigen (Ag)
substances that can induce an
immune response and are recognized
by a particular immunoglobulin or
TCR, and so can serve as the target of
an immune response.
2 important properties of Ag
---the ability for inducing
an IR, including induce
production of antibody and
effector T cell
Combine specifically
 Immunogenicity
antigen
↓
IS
↓induce
IR
↓
products of IR
(Ab/effector T cells)
Antigenicity/immunoreactivity
---the ability to combine
specifically with the Ab or
effector T cell induced by its
own
→immunogenicity
→antigenicity
Complete antigen & hapten
A.Complete antigen
---Substances that have both immunogenicity and immunoreactivity(antigenicity)
B.Hapten
---Substances that have immunoreactivity ,
but lack of immunogenicity
(二硝基苯)
combine with
•
• Hapten couple(偶联) to protein or other
carriers to form complete antigen
• hapten+carrier = complete antigen
Chapter 2
characteristics of Ag
specificity
most of the immunogens
encounterd in nature are complex
assemblages made up of several
different types molecules, not all of
which are antigenic
epitope
the specific site to which a
particular immunoglobulin or
TCR binds
antigenic determinant (AD)
epitope
 Definition
the specific site to
which a particular
immunoglobulin or
TCR binds
AD
Ag
B
抗原
antigen
T
Ag
antigen
Ag
Specificity of antigen
多
价
AD 抗
原
多
价
抗
原
induce
specificity of
immunogenicity
AD
specificity of
immunoreactivity
Specificity of antigen
Classification of epitope
B cell epitopes
• Linear epitope
• Conformational epitope
• T cell epitopes
B cell epitope
the regions that are recognized
by immunoglobulins
• linear epitopes
• Conformational epitopes
构像表位和线性表位
T cell epitope
• Proteinaceous Ag degraded into
peptides
• Some of peptides associate with an
MHC protein
• Peptide-MHC complex are presented
on the APC surface
• TCR recognizes peptide-MHC complex
Macrophages Take Up Antigen
Into Vesicles and Present Peptide
Fragments From Proteins
in MHC-II
CD4+Th细胞
外源性抗原加工、处理和呈递示意图
Common Ag and cross reaction
Some Ag usually strip multi-Ag
epitope and can react with Ab or
activate lymphocyts inducing
• By themselves
• By other inducing
Ag 1
Ab 1
Ab 2
Ag 2
Common Ag
Different Ag which contain
sameness or similitude Ag epitope
cross reaction
Ab or activate lymphocyte react
with sameness or similitude Ag
epitope in different Ag
Ag 1
Ab 1
Ab 2
Ag 2
（一）抗原的异质性与共同表位
Common Ag and cross reaction
Ag1
Ag2
Foreignness
• Only molecules that are foreign to
the host are immunogenic
• Immune system can recognize self
and non-self
Chapter 3
factors influencing
immunogenicity
Important factors
• Foreigness(异物性)
• Physicochemical characteristics
• Host
• Mode of contact
Foreigness
 Non-self substances: do not contact
sufficiently with immune cells during
embryonic period
Self tissue: tolerance
Physicochemical properties of Ag
 Chemical property
 Molecule size
Molecule Complexity
conformation and accessibility
（分子构象和易接近性）
Chemical property
• Proteins are the most effective
immunogens
• Nucleic acids and most lipids are
antigenic but not immunogenic
Hapten
Molecular size
• Molecular weights greater than
100,000
• Most other species smaller than
10,000 usually are not
immunogenic
A few substances with molecular
weights below 1,000 can induce
immune responses when bound to a
larger, host-derived macromolecule.
Molecular complexity
• Homopolymers of a single amino
acid may be poor immunogens
• Copolymers of two or more are
often quite active
conformation and accessibility
Immunogenicity +++
±
+++
Effect of host
• The ability to respond to a particular
immunogen is genetically predetermined
 Genetic characteristics of the host
 Age, sex, and state of health
Mode of contact
• Dosage
• Route
intracutaneous
subcutaneous
intramuscular
intravenous
oral
Chapter 4
classification of Ag
TD-Ag and TI-Ag
TD-Ag
• Most protein Ag require Ag-specific T
cell help to generate an Ab response
• The immune response to most Ag
depend on both T cells and B cells
TI-Ag
Some Ag do not require the
presence of helper T cells
Classification based on
relationship with host
Heterophilic Ag
• Forssman Ag
• A kind of common Ag,
• Exists in human, animals and
microorganism
• Related to some diseases
rheumatic fever:
• 2 weeks after infection
• fever, migratory polyarthritis, carditis
• immunologic cross-reaction between
bacterial Ag and human heart and
joint tissue
• Can be prevented by treatment of
infection within 8 days
Bacteria induced
producing Ab
Ab bind epitope of
bacteria
Bacteria were
eliminated
Ab bind epitope of
host tissue
Xenogenic Ag
The Ag come from different genus
and generic
The important xenogenic Ag:
• Pathogenic microorganism
• Plant protein
• Animal serum
• Heterogeneity organ implant
Animal serum
•
•
•
•
The serum come from animal
Contain Ab
Can treat or prevent disease
May act as an immunogen
Allogenic Ag
The specific Ag exists in different
individual of same genus
• ABO red cell blood type Ag
• Rh Ag system
• HLA
Autoantigen
• Oneself component can induce
body to self immune response
enshrounded Ag
isolation Ag
self-Ag occur change or decorated
Chapter 5
non-specific stimulators
Super Ag (SAg)
• Has the capability of activating
1%-10% of peripheral T cells
• Exposure to a SAg can lead to
massive T cell activation
Adjuvant
The response to an immunogen
mixed with adjuvants can often be
enhanced