Antigens can be

Antigens can bind to effector cells or products, thereby exerting adaptive immune response effects

Substances that are both immunogenic and antigenic, such as most proteins

Small molecular substances that only have antigenicity but no immunogenicity (possibly because the molecular weight is too small and cannot be recognized by immune cells)

Such as polysaccharides, lipids, certain drugs, etc.

After the hapten is cross-linked or combined with a carrier such as a macromolecular protein, it can also become a complete antigen.

B cell antigen receptor BCR recognizes hapten determinants

Proteins that confer immunogenicity to haptens, commonly used carriers include

The antigen stimulates the body to produce an adaptive immune response and its binding to the response effector products shows specificity.

A specific antigen can only stimulate the body to produce activated T/B cells or antibodies against that antigen, and can only specifically bind to that lymphocyte or antibody.

Application: Immunological testing

Small molecule group in an antigen molecule that determines antigen specificity

The site where the antibody molecule binds to the antigen

Ligands recognized and bound by immunologically active cell surface antigen receptors (TCR/BCR)

Such as amino acids, polysaccharides, nucleotides

Natural antigens generally have multiple (multivalent) epitopes

A hapten is equivalent to an independent antigenic epitope. The antigenic epitope separated from the antigen macromolecule also belongs to the hapten.

conformational epitope

sequential epitope

T cell epitope

B cell epitope

After enzymatic hydrolysis of natural antigen molecules, B cell conformational epitopes are easily inactivated.

Binding to antibody molecules

Determines the specificity of binding to antibody molecules

cause immune cross-reaction

Example: Penicillin allergy

Antigens with common epitopes

Antibodies produced by the body stimulated by common antigenic determinants can combine with multiple antigens to produce immune responses.

Alien substances: substances that the immune system has not been exposed to during the embryonic period

Self-substances: substances that the immune system is exposed to during embryonic life

Immunogenicity intensity: protein>polysaccharide/lipopolysaccharide>nucleic acid/histone

Generally speaking, the larger the molecular weight, the more antigenic epitopes, the more complex the structure, and the stronger the immunogenicity.

The more complex the structure, the stronger the immunogenicity

The spatial location of the antigenic epitope

Immunogenicity intensity: Aggregated protein > Granular protein > Soluble protein

The body's ability to respond to antigens is controlled by a variety of genetic genes, especially the "major histocompatibility complex" (MHC)

MHC is highly polymorphic, making different individuals respond to the same antigen at different levels.

Youth is stronger than infancy and old age

Females are more capable of inducing antibodies than males, but the response ability of pregnant individuals is significantly suppressed

Moderate

too high or too low

Ability to elicit an immune response: intradermal/subcutaneous > intramuscular > intraperitoneal > intravenous > oral

Appropriate interval (1~2 weeks)

frequent contact

Can significantly alter the intensity and type of immune response

Need T cell help

There are many types of determinants, including B/T cell epitopes

MHC-restricted (because MHC is responsible for T cell activation)

Can induce humoral immunity and cellular immunity

Can produce IgM, IgG, IgA and other antibodies (mainly IgG)

Have immune memory

No need for T cell help

A large number of determinants, regular arrangement, and repeated B cell epitopes

No MHC restriction

Produces only IgM antibodies

Cannot induce cellular immunity

There is no immune memory, so TI-Ag cannot induce another immune response.

Common antigens that exist among humans, animals, and microorganisms regardless of species

Hemolytic Streptococcus-human glomerular basement membrane-myocardial tissue

Escherichia coli O14 lipopolysaccharide-human colon mucosa

An antigenic substance derived from another species.

Pathogenic microorganisms, plant proteins, animal antisera, xenografts

Antigens that exist between different individuals of the same species.

Blood group antigens, HLA

cryptic antigen

modified autoantigen

Common types: eye lens protein, sperm, brain tissue, thyroglobulin

The complementarity determining regions (CDRs) within antibodies, TCRs, and BCRs serve as epitopes to induce specific antibodies.

Newly synthesized antigen in antigen-presenting cells

Viral proteins synthesized by virus-infected cells (virus progeny are synthesized by the host), tumor antigens

APC: synthesis, processing, presentation

Not synthesized by APC, but derived from antigens outside APC

Bacteria, fungi, parasites

APC: Processing and Presentation

natural antigen

artificial antigen

particulate antigen, soluble antigen

Protein antigen, polysaccharide antigen, nucleic acid antigen

Transplantation antigens, tumor antigens, autoantigens

Allergens (allergens)

tolerogen

A non-specific immune enhancer that is injected into the body in advance or together with the antigen, and can enhance the body's immune response to the antigen or change the type of immune response.

It is non-immunogenic and cannot elicit an immune response

Change the physical properties of the antigen and prolong the retention time of the antigen in the body - sustained release

Enhance the coordinated stimulation signals required for immune cell activation and stimulate antigen-presenting cells

Make the antigen easily phagocytized by phagocytes and enhance the processing and presentation of antigen by phagocytes

Promote lymphocyte proliferation and differentiation and enhance the body's immune response

Immunization, animal serum preparation; adjuvant treatment for patients with tumors or chronic infections

biological adjuvants

inorganic compounds

synthetics

organic matter

Liposomes