浙江大学医学免疫学经典课件03-antigen

Antigen
Ⅱ. specificity 1. epitope (antigenic determinant ) 抗原决定簇（基），表位 - the portion of the antigen that binds specifically with the binding site of an antibody or a receptor on a lymphocyte. - the size of an epitope is approximately equivalent to 5-15 amino acids.
Antigen
Types of antigens
Th: Thymus-dependent antigen(TD-Ag) Thymus-independent antigen(TI-Ag) Relative: Xenogenic antigen Allogenic antigen Autoantigen Heterophilic antigen Idiotypic antigen
Antigen
TI-Ag Thymus -independent antigens are antigens which can directly stimulate the B cells to produce antibody without the requirement for T cell help In general. only B cell epitope Humoral immunity Antibody :IgM No Immune memory polysaccharides are TI- antigens.
Antigen
4.common antigen and cross-reaction
Antigen
Factors influencing immunogenicity
A. Contribution of the antigen 1.chemical Composition – protein polysaccharide nuclear acid 2. size - There is not absolute size above which a substance will be immunogenic. In general, the larger the molecule the more immunogenic it is likely to be.
免疫原性
T
Ag
T
浆细胞
致敏T细胞
B
抗体
-⑵antigenicity or immunoreactivity (react with the products of a specific immune response) 抗原性
T
B T
浆细胞 抗体
Ag
致敏T细胞
3. Immunogen -A substance that induces a specific immune response.
Complete Ags ： have the properties of immunogenicity and immunoreactivity. Hapten （ 半 抗 原 ） ： have the property of immunoreactivity but not immunogenicity . - A substance that is non-immunogenic but which can react with the products of a specific immune response.
Antigen
3.chemical complexity- ILeabharlann Baidu general, the
more complex the substance is chemically the more immunogenic it will be. An increase in the chemical complexity of a compound is accompanied by an increase in its immunogenicity
B cell epitope
BCR unnecessary natural polypeptide polysaccharides conformational determinant ; linear determinant surface of Ag
●Location
Ag
Antigen
3. epitope-carrier effect
1. Genetic Factors - Some substances are immunogenic in one species but not in another. Similarly, some substances are immunogenic in one individual but not in others (i.e.responders and non-responders). 2. Age - Age can also influence immunogenicity. Usually the very young and the very old have a diminished ability to mount and immune response in response to an immunogen.
Antigen
C. Method of Administration 1. Dose - The dose of administration of an immunogen can influence its immunogenicity. 2. Route - Generally the subcutaneous route is better than the intravenous or intragastric routes. The route of antigen administration can also alter the nature of the response 3. Adjuvants
Antigen
TI-Ag
Thymus -independent antigens can be subdivided into Type 1 and Type 2 based on their ability to polyclonally activate B cells.
Type 1 TI-Ag(LPS) are polyclonal activators while Type 2 are not.
构象表位
线性表位
Binding site for antigen
Binding site for antigen
Antigen
★ B cell epitope ★ T cell epitope
Antigen
Antigen
T cell epitope
●Receptor TCR ●APC,MHC necessary ●Character linear short peptide linear determinant
Antigen
Haptens are small molecules which could never induce an immune response when administered by themselves but which can when coupled to a carrier molecule. hapten + carrier → complete Ag
Antigen
TD-Ag Thymus -dependent antigens are those that do not directly stimulate the production of antibody without the help of T cells. B cell epitope ＋ T cell epitope Humoral immunity and cellular immunity Antibody: five types Immune memory Proteins are thymus -dependent antigens.
第二章 抗原
Chapter Ⅱ
Antigen（Ag）
Antigen
KNOWLEDGE POINTS
1. Concept
2. Immunogenicity and specificity
3. Requirements for immunogenicity
4. Types of antigens
5. Superantigen and adjuvants
▲sequential epitope:
All of the amino acid or sugar residues that form a given epitope are positioned sequentially in the linear sequence of a protein or polysaccharide antigen.
Concept
1. Antigen (Ag) – the substances that are recognized by TCR/BCR or antibody and induce a specific immune response.
Antigen
2.Properties of Ag
-⑴immunogenicity
epitope
Antigen
description
One epitope
example
haptens
Many epitopes of the same specificity
Many epitopes of different specificity
Many polysaccharides, homopolymers
Antigen
Foreignness and specificity
Ⅰ. Foreignness - The immune system normally discriminates between self and non-self such that only foreign molecules are immunogenic.
proteins
Representation of some possible antigenic structures
Antigen
2. the types of epitope ▲conformational epitope:
Some epitopes form only when the critical residues are brought together in space through folding of the polypeptide or polysaccharide chain into its normal three-dimensional conformation.
5. Tolerogen, allergen
Tolerogen: an antigen that induces a state of specific immunological unresponsiveness Allergen: a substance capable of inducing allergy or specific hypersensitivity. pollens, dust, drugs, and foods…
4.conformation 5. accessibility 6. physical form - In general particulate
antigens are more immunogenic than soluble ones.
Antigen
Antigen
B. Contribution of the host