Antigens, haptens and immunogens were discussed. Key points:
- Antigens are molecules that induce an immune response through binding antibodies or T cells. Immunogens can induce immune responses while antigens may only bind antibodies/T cells.
- Antigens are classified based on origin (exogenous, endogenous, autoantigens), chemical structure (proteins, polysaccharides etc.), and type of immune response generated (T cell dependent/independent).
- Immunogenicity depends on antigen properties like size, structure and degradability as well as the exposed biological system. Larger complex molecules tend to be more immunogenic.
This document defines key terms related to antigens and the immune response. It discusses how antigens stimulate an immune response by interacting with antibodies and T cells. There are different types of antigens including exogenous antigens that enter the body from outside, endogenous antigens generated inside cells, autoantigens that are recognized by the immune system in autoimmune diseases, and tumor antigens expressed by cancer cells. The document also describes properties of antigens like immunogenicity and antigenicity, and characteristics of antigenic epitopes recognized by B cells and T cells. It classifies antigens as thymus-dependent or -independent and discusses conventional antigens, superantigens, and adjuvants that enhance immune responses.
B cell Activation by T Independent & T Dependent Antigens-Dr C R MeeraMeera C R
During humoral immune response, Ab production is brought about by B lymphocytes. Based on the ability to induce Ab formation, antigens can be classified into T independent and T dependent antigens. Some antigens can directly induce the B cells to produce the Abs and are called T Independent Ans. However, some Ans require the help of T lymohocytes for the production of Abs from B cells. These Ans are called T Dependent Ans.
Transplantation refers to transferring cells, tissues or organs from one site to another. The first successful human kidney transplant occurred between identical twins in Boston in 1954. There are four main types of transplants - autograft, isograft, allograft, and xenograft - which differ based on the genetic similarity between the donor and recipient. Autografts have no immune response, while xenografts between different species have the most vigorous rejection response.
The document summarizes the four main types of hypersensitivity reactions:
1. Type I reactions are immediate and mediated by IgE antibodies, causing conditions like allergic asthma from mast cell degranulation.
2. Type II reactions involve antibodies binding to antigens on a patient's own cells, activating complement and causing cell lysis in diseases like autoimmune hemolytic anemia.
3. Type III reactions occur when immune complexes deposit in tissues, activating complement and causing inflammation in diseases like serum sickness and lupus nephritis.
4. Type IV reactions are delayed cell-mediated responses, seen in contact dermatitis and tuberculin reactions, involving T cells and macrophages.
The document discusses the nature of antigens and the major histocompatibility complex (MHC). It defines immunogens and antigens, noting that immunogens can trigger an immune response while not all antigens are immunogens. Antigens are usually large proteins or polysaccharides from foreign organisms. Factors like age, health, dose, and route of exposure can influence the immune response. The document also discusses epitopes, haptens, adjuvants, and the relationship of antigens to the host (autoantigens, alloantigens, heteroantigens). It provides details on MHC genes, class I and class II MHC structure and function in antigen processing and presentation to T cells.
1. An immunogen is an agent capable of inducing an immune response, while an antigen is any agent capable of binding to components of the immune system. All immunogens are antigens, but not all antigens are immunogens.
2. Haptens are low molecular weight compounds that are incapable of inducing an immune response alone but can do so when conjugated to a carrier molecule like a protein.
3. For a substance to be immunogenic, it must be foreign, have a high molecular weight and chemical complexity, be degradable, and interact with MHC molecules.
Cell-mediated immunity involves T cells that recognize and eliminate intracellular pathogens. MHC class I presents endogenous antigens to activate CD8+ cytotoxic T cells to kill virally infected cells, while MHC class II presents exogenous antigens to CD4+ helper T cells to upregulate immune functions against bacteria. Humoral immunity involves B cells maturing into plasma cells upon antigen recognition, secreting antibodies, and leaving memory B cells to facilitate a faster response upon reexposure.
The document summarizes the key organs and tissues of the immune system. It discusses the primary lymphoid organs of bone marrow and thymus, where lymphocytes mature. It also describes the secondary lymphoid organs of lymph nodes, spleen, and lymphoid tissues like Peyer's patches and tonsils, which are the sites where immune responses occur. Mucosal-associated lymphoid tissues contain aggregates of immune cells that defend against antigens entering mucosal surfaces.
Antigen
Antigen is a substance which binds specifically with the products (antibodies, T-cells) of the immune system.
Its ability to bind with antibodies is called antigenicity.
Immunogen
It is a substance which produces an immune response as well as binds to its products.
So, immunogen is an antigen as well but antigen need not be immunogen.
The property of producing an immune response is called immunogenicity.
This document defines and describes antigens and what makes an effective antigen. It notes that an antigen is any substance that induces an immune response and antibodies specifically bind to antigens. The best antigens are large, complex proteins that are foreign to the host. Characteristics like size, stability, complexity and foreignness influence a substance's ability to act as an antigen. Bacterial proteins, viral capsids and parasitic molecules can all serve as antigens. The document also discusses epitopes, haptens, adjuvants and cross-reactivity in antigen-antibody binding.
T CELL ACTIVATION AND IT'S TERMINATIONpremvarma064
T cell activation requires two signals: 1) recognition of antigens displayed on antigen-presenting cells by T cell receptors and 2) co-stimulatory signals through molecules like CD28. This leads T cells to proliferate, differentiate into effector and memory cells, and perform effector functions. Proper activation requires interaction between T cells and antigen-presenting cells in lymphoid tissues, where costimulatory molecules are highly expressed. Dysregulation of T cell activation can lead to autoimmunity or susceptibility to infection.
The document discusses cytokines, which are proteins that mediate communication between cells of the immune system. It describes the different types of cytokines, including interleukins produced by T-helper cells, lymphokines produced by lymphocytes, and monokines produced by monocytes. The document outlines the roles and functions of specific cytokines like IL-1, IL-2, TNF, IFN-γ and GM-CSF. It also discusses how cytokines are classified based on their structure and roles in innate versus adaptive immunity.
Haptens are small molecules that are antigenic but not immunogenic on their own. They are unable to induce an immune response because they cannot activate helper T cells due to their inability to bind MHC proteins or activate B cells directly as they are univalent. However, when haptens are covalently bound to a carrier protein, they form immunogenic conjugates that can induce an immune response by activating helper T cells and B cells. Pioneering work by Karl Landsteiner demonstrated that antibodies produced against hapten-carrier conjugates were specific for the hapten and carrier epitopes. Common examples of haptens include drug molecules, peptides, and steroids. Hapten-protein conjugates can cause drug
The document summarizes the cells and organs of the immune system. It describes how hematopoietic stem cells in the bone marrow give rise to myeloid and lymphoid progenitor cells. These progenitor cells then differentiate into various immune cells including granulocytes, lymphocytes, dendritic cells, macrophages, and others. It also outlines the primary and secondary lymphoid organs including the bone marrow, thymus, spleen, lymph nodes, and mucosal tissues that support the development and activation of immune cells.
This document discusses organ transplantation and immunological basis of allograft rejection. It defines organ transplantation as moving an organ from one body to another to replace a damaged organ. Organs that can be transplanted include the heart, kidneys, liver, lungs and pancreas. It describes the different types of transplants and mechanisms of allograft rejection, including cell-mediated immunity and humoral immunity. It also classifies allograft rejection into hyperacute rejection, acute rejection and chronic rejection.
IT CONTAINS THE LATEST INFORMATION ABOUT MHC MOLECULE WHICH WILL BE HELPFUL FOR B.SC /M.SC/CSIR-NET/DBT-JRF/GATE STUDENTS. THIS IS IN VERY SIMPLE AND LUCID MANNER TO UNDERSTAND AND ONE CAN EASILY OPT FOR THIS TO PREPARE NOTES.
Major Histocompatibility complex & Antigen Presentation and ProcessingSreeraj Thamban
The document discusses the major histocompatibility complex (MHC) and antigen processing and presentation. It describes MHC molecules as polymorphic glycoproteins that play a role in discriminating self from non-self and participate in both humoral and cell-mediated immunity. MHC class I molecules present endogenous antigens on most nucleated cells and interact with CD8+ T cells. MHC class II molecules present exogenous antigens on antigen-presenting cells and interact with CD4+ T cells. Antigens are processed into peptides of appropriate size and bound motifs to be presented in the binding groove of MHC molecules.
A vaccine is an antigenic material that stimulate adaptive immunity to a disease. Vaccines can prevent the effects of infection by many pathogens. Vaccine’s are generally considered to be the most effective method of preventing infectious diseases. The material administered can either be live but weakened forms of either bacteria or viruses, killed or inactivated forms of these pathogens, or purified material such as proteins.
This document discusses antibody engineering techniques. It begins with an introduction and overview of antibody structure and function. It then describes several methods for engineering antibodies, including the hybridoma method, chimeric method, and humanized method. It provides details on each method and how they work to produce engineered antibodies. Applications of engineered antibodies are also mentioned. Throughout, the document discusses advances in recombinant antibody production and fully human monoclonal antibody techniques.
This document provides information on types of antigens and factors that determine antigenicity. It discusses different types of antigens, including exogenous, endogenous, autoantigens, and alloantigens. It also covers the chemical nature of antigens, including proteins, polysaccharides, nucleic acids, and lipids. Additionally, it examines factors that influence immunogenicity, such as foreignness, molecular size, chemical nature, physical form, antigen specificity, and others. Superantigens are also discussed as a class of antigens that cause non-specific polyclonal activation of T-cells.
...Serological Technique Presentation Group 8 th.pptxBIOGENLABS
This document discusses key concepts related to antigens and immunogens. It defines antigens and immunogens, and notes that immunogens are molecules capable of activating lymphocytes to stimulate an immune response. Epitopes are described as the immunologically active regions of antigens that bind to antibodies or lymphocyte receptors. The document then discusses the chemical nature, types, properties, and factors influencing the immunogenicity of antigens.
This document discusses multidrug resistance bacteria and contains information on antigens, immunogens, epitopes, types of antigens, properties that influence immunogenicity, and factors that determine antigenicity. It defines antigens and immunogens, and describes different types of antigens such as exogenous, endogenous, autoantigens, complete vs incomplete antigens. It also discusses epitopes, chemical nature of antigens, and properties like molecular size, chemical composition, and physical form that influence immunogenicity.
Immunogens are substances that can induce an immune response, while antigens are substances that can bind to antibodies or T-cell receptors. Not all antigens are immunogenic. The properties of an effective immunogen include foreignness, molecular size over 100,000 Daltons, chemical complexity, and the ability to be processed and presented by antigen-presenting cells. The immunogenicity of a substance depends on additional factors like dosage, route of administration, use of adjuvants, and host genetics. Antigens can be classified as exogenous, endogenous, autoantigens, or complete versus incomplete antigens.
1) An antigen is any substance that can induce an immune response by being immunogenic or antigenic. Immunogenicity is the ability to induce an immune response through B and T cells. Antigenicity is the ability to bind to antibodies or T cell receptors.
2) An epitope is the smallest part of an antigen that can induce an immune response. It consists of 4-5 amino acids or sugars that bind to T or B cell receptors.
3) A hapten is a small molecule that is not immunogenic on its own but can bind antibodies when attached to a larger carrier molecule, making it immunogenic.
Antigens are substances that induce an immune response and can combine with immune system products like antibodies and T cell receptors. They come in various types, including complete antigens that induce antibody formation on their own and incomplete antigens or haptens that require a carrier protein. Antigens are classified based on their ability to induce T cell dependent or independent responses. Superantigens can directly activate T cells without antigen processing. Diseases may result from exposure to bacterial or viral superantigens.
Antigen is a substance that induces an immune response through the formation of antibodies or activation of T cells. Antigens can be proteins, polysaccharides, nucleic acids, or lipids. Immunogens are antigens that are capable of inducing an immune response on their own due to their large size, while haptens require a carrier molecule. Antigenicity refers to the ability to bind antibodies, while immunogenicity is the ability to induce an immune response. Factors like molecular size, chemical composition, dose, and route of administration can influence a substance's immunogenicity. Adjuvants are substances that enhance the immune response to an immunogen when used together.
Antigen is any substance that induces an immune response in the body. There are two main types: complete antigens that can induce an immune response on their own, and incomplete antigens or haptens that require a carrier molecule to become immunogenic. Antigens are recognized by immune cells through antigen determinants or epitopes. For a response, antigens must be processed and presented by antigen-presenting cells to be recognized by T cells through MHC molecules. The properties of an antigen like its size, structure, and route of administration influence its ability to induce an immune response.
This document discusses antigens and concepts in vaccine development. It begins by defining antigens and classifying them as exogenous or endogenous. It then discusses the differences between immunogenicity and antigenicity, and lists factors that influence immunogenicity such as molecular size, chemical composition, and adjuvants. The document also covers epitopes, mitogens, and superantigens. Finally, it discusses the different stages of vaccine development from pre-clinical to clinical trials and licensing, and methods used in vaccine manufacturing.
Antigen and antibody are essential components of the immune system. Antigens are substances that induce an immune response through the production of antibodies. The key properties of antigens are that they are foreign, have specific epitopes that antibodies bind to, and can range in size. Antibodies are Y-shaped proteins produced by B cells in response to antigens. The five major classes of antibodies are IgG, IgM, IgA, IgD, and IgE, which have different structures and functions such as pathogen neutralization, opsonization, and activation of immune cells.
This document provides an overview of immunological disorders and HIV/AIDS. It discusses the components of the immune system including innate and adaptive immunity. It describes the four types of hypersensitivity reactions and common disorders like allergies. It then focuses on HIV/AIDS, explaining how it weakens the immune system, the types of HIV, modes of transmission including sexually, blood-to-blood contact, and from mother to child, as well as the pathogenesis and clinical manifestations of HIV infection.
1. An antigen is any substance that causes the immune system to produce antibodies against it. Antigens can be external substances like viruses, bacteria, and pollen that enter the body, or they can be generated internally through infections or metabolism.
2. There are different types of antigens including exogenous antigens from outside the body, endogenous antigens produced internally, autoantigens that cause autoimmune disorders, and tumor antigens on cancer cells.
3. Antigens have antigenic determinants called epitopes that bind to receptors on lymphocytes and stimulate an immune response. Adjuvants are substances used in vaccines to enhance the immune response to antigens.
This document discusses antigens and haptens. It defines antigens as macromolecules that elicit an immune response through antibody formation. It classifies antigens as exogenous or endogenous, and further divides endogenous antigens. It distinguishes immunogenicity from antigenicity and defines haptens as low molecular weight compounds that are antigenic but not immunogenic unless coupled to a carrier protein. It provides examples of haptens and describes tests used to detect antigens and haptens.
Here are five things to know about coronavirus tests: PCR and antigen tests are the most common but they work differently. While antigen tests look for proteins ...
An antigen is any substance that causes your immune system to produce antibodies against it. This means your immune system does not recognize the substance, and is trying to fight it off. An antigen may be a substance from th
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Discover the Best Sexologist in Patna: Expert Care at Kayakalp Clinic
Kayakalp Clinic - Best Sexologist in Patna
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Learning objectives:
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2. Explain the mechanism of action of insulin
3. Discuss the metabolic functions of insulin
4. Elucidate the effects of insulin on adipose tissue, skeletal muscle, and liver
5. Enlist the factors which stimulate and inhibit the release of insulin
6. Explain the mechanism of action of glucagon
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1. Chapter 79, Guyton and Hall Textbook of Medical Physiology, 14th edition
2. Chapter 24, Ganong’s Review of Medical Physiology, 26th edition
3. Chapter 39, Berne and Levy Physiology, 7th edition
4. Chapter 19, Human Physiology, From Cells to Systems by Lauralee Sherwood, 9th edition
5. Chapter 3, Endocrine and Reproductive Physiology, Bruce A. White and Susan P. Porterfield, 4th edition
6. Insulin and Insulin Resistance, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1204764/
7. Complications of diabetes mellitus,
https://pdb101.rcsb.org/global-health/diabetes-mellitus/monitoring/complications
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Principles of Cleaning
Nonsurgical root canal treatment is a predictable method of retaining a tooth that otherwise would require extraction. Success of root canal treatment in a tooth with a vital pulp is higher than that of a tooth that is necrotic with periradicular pathosis. The difference is the persistent irritation of necrotic tissue remnants, and the inability to remove the microorganisms and their by-products. The most significant factors affecting this process are tooth anatomy and morphology, and the instruments and irrigants available for treatment. Instruments must contact and plane the canal walls to debride the canal.
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Currently there are no reliable methods to assess cleaning. The presence of clean dentinal shavings, the color of the irrigant, and canal enlargement three file sizes beyond the first instrument to bind have been used to assess the adequacy; however, these do not correlate well with debridement. Obtaining glassy smooth walls is a preferred indicator. The properly prepared canals should feel smooth in all dimensions when the tip of a small file is pushed against the canal walls. This indicates that files have had contact and planed all accessible canal walls thereby maximizing debridement (recognizing that total debridement usually does not occur).
Principles of Shaping
The purpose of shaping is to
1) facilitate cleaning and
2) provide space for placing the obturating materials.
The main objective of shaping is to maintain or develop a continuously tapering funnel from the canal orifice to the apex. This decreases procedural errors when cleaning and enlarging apically. The degree of enlargement is often dictated by the method of obturation. For lateral compaction of gutta percha the canal should be enlarged sufficiently to permit placement of the spreader to within 1-2 millimeters of the corrected working length. There is a correlation between the depth of spreader penetration and the apical seal.5 For warm vertical compaction techniques the coronal enlargement must permit the placement of the pluggers to within 3 to 5 mm of the corrected working length.6
As dentin is removed from the canal walls the root is weakened.7 The degree of shaping is determined by the preoperative root dimension, the obturation technique, and the restorative treatment plan. Narrow thin roots such as the mandibular incisors cannot be enlarged to the same degree as more bulky roots such as the maxillary central incisors. Post placement is also a determining factor in the amount of coronal dentin removal.
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2. OUTLINES:
• Antigens
Definition of terms
• Chemical nature of antigens
• Classification of antigens
• Immunogens
• Factors influencing Immunogenicity
• Immunogens and epitopes
• Haptens
• References
3. ANTIGENS
Antigens:
An antigen is a molecule that is recognized by specific antibodies or
the TCR on T cells
Its ability to bind with antibodies or T-cell is referred to as
antigenicity.
The foreign substances (antigens) that induce an immune response
possess two properties; immunogenicity and antigenicity.
4. Cont…
Immunogenicity:
Ability of an antigen to induce immune response in body (both
humoral and/or cell mediated).
•B cells + antigen → effector B cells (plasma cell) + memory B cells
•T cells + antigen → effector T cells (helper T cell or cytotoxic T cell)
+ memory T cells
5. Antigenicity:
• Ability of an antigen to combine specifically with final products
antibodies and/or T cell-surface receptors.
Note: Immunogenic substances are always antigenic, whereas
antigens are not necessarily immunogenic (e.g., Autologous
serum proteins).
6. Epitopes (antigenic determinant)
is the actual molecular structure that interacts with a single
antibody molecule or TCR.
Some epitopes are found inside the antigen (internal), only
expressed after the antigen has been "processed" by a
phagocytic cell. .
7. Antigens are multivalent; that is, an antigen molecule carries a
number of different epitopes, sometimes hundreds of them, some
specifying antibody "A", others antibody "B", and so forth, the
valence of an antigen is equal to the total number of epitopes the
antigen possesses.
Paratope:
• Specific site of an antibody that reacts with the corresponding
epitope of an antigen
11. Adjuvants:
The word "adjuvant“- Latin word adiuvare, meaning to help or aid.
Substances which enhances the body’s immune response to an
antigen
They are not immunogenic alone but enhance immunogenicity of
an added immunogen.
When mixed with an antigen and injected with it enhance the
immunogenicity of that antigen.
These substances enhance the immunogenicity of molecules
without altering their chemical composition.
12. Uses of adjuvants in immunology
Adjuvants affect the immune response in various ways:
• To increase the immunogenicity of weak antigens
• To enhance speed and duration of immune response
• To stimulate and modulate humoral responses, including
antibody isotype
• To stimulate cell-mediated immunity
• Enhance immune responses in immunologically
immature patients, particularly infants
• To decrease the dose of antigen required; reducing costs
and eliminating inconvenient requirements for booster
shots
13. Summary of adjuvants approved for human use
Adjuvant Description
Approved vaccine
products
Aluminium-based
mineral salts (Alum)
Aluminium phosphate,
Calcium phosphate,
Aluminium hydroxide
-Anthrax
-Hepatitis A
MF59
Submicron oil-in-water
emulsion
Influenza
Monophosphoryl lipid A
(MPL)
Bacteria-derived
immunostimulant
Hepatitis
Virosomes
Spherical vesicles
containing viral
membrane proteins in
the lipid membrane
Hepatitis
Influenza
14. Classification of antigens
Antigens can be classified based on many characters:
i. Based on their origin
ii. Based on chemical nature and structure
iii. Based on their Immunogenicity
iv. Based on cellular response generated
I. Based on their origin
Exogenous antigens
Endogenous antigens
Autoantigens
15. Exogenous antigens:
• Enters the body from outside inhalation, ingestion or injection
• Enter cells by endocytosis or phagocytosis and starts circulating in
the body fluids and trapped by the APC
• Some antigens starts as exogenous endogenous e.g intracellular
viruses, bacteria, and fungi.
Endogenous antigens:
• Body’s own cells or antigenic products that are produced from
normal cell metabolism
• Processed by macrophages which are later accepted by cytotoxic
T-cells. Includes xenogeneic, autologous and isoantigenic/allogenic
antigens e.g Blood group antigens, HLA(Histocompactibility
leukocyte antigen
16. Autoantigens
• Antigens that stimulates autoantibodies in the organism
that produce it
• Are self antigens that involved in autoimmune disease
pathogenesis
• Usually normal proteins/complex of proteins that is
recognized by the immune system as nonself, E.g
Nucleoproteins, NA.
• Another good example is p53 which have been described
as an autoantigen in several autoimmune diseases eg SLE
and many cancer diseases
17. II. Based on chemical nature and structure
• Proteins
– Majority of immunogens are proteins
– Proteins are usually very good immunogens.
• Polysaccharides
– Pure polysaccharides and lipopolysaccharides are good
immunogens.
• Nucleic Acids/Nucleoproteins
– Nucleic acids are usually poorly immunogenic..
• Lipids
– In general lipids are non-immunogenic but may be haptens.
18. III. Immunogenicity(Immune response)
Complete antigen (Immunogen):
Able to generate immune response by themselves
High molecular weight >10000D
Proteins or polysaccharides
Incomplete antigen (hapten):
Can not induce immune response on their own,
needs a carrier molecule
Low molecular weight
19. IV. Based on cellular response generated
Biological classes of antigens
• Depending on the mechanisms of inducing antibody formation,
antigens are classified as:
T cell independent (TI) antigens.
T cell dependent (TD) antigens.
Superantigens
T-independent antigens:
• Can directly stimulate B cells to produce Ab without the help of
T-cells
• Generally they are polysaccharides
• Induce B cells to produce only Ig M
• No immune memory
• Can not induce CMI
20. Properties of T-independent antigens
Polymeric structure:
• Same antigenic determinant epitope repeated many times
Polyclonal activation of B cells:
• Can activate B cell clones specific for other Ags
• Subdivided into type 1 and 2 based on their ability to
polyclonally activate B cells
• Type 1 are polyclonal activators while type 2 are not.
Resistance to degradation:
• More resistant to degradation persists for a longer
period of time and continue to stimulate the immune
system.
21. T-cell dependent antigens
• Most of the normal antigens are T cell dependent, they
are processed and presented by antigen-presenting cells
(APCs) to T cells which leads to T cell activation.
• Activated T cells secrete cytokines that in turn stimulate
the B cells to produce antibodies.
• Do not directly stimulate the production of Ab without
the help of T cells.
• Generally they are proteins
• Stimulate B cells to produce IgM, IgG and Ig A
• Can induce CMI, have immune memory
23. Superantigens
• Superantigens are the third class of biological antigens.
• There are different types such as bacterial, viral and
fungal superantigens
• The unique feature of superantigens is, they can
activate T cells directly without being processed by
antigen presenting cells (APCs).
• Intact protein binds to variable region of β chain on TCR
of T cells and to MHC class II on antigen presenting cells
(APC)
26. Immunogens
• To protect against infectious disease, the immune system recognize
bacteria, bacterial products, fungi, parasites, and viruses as
immunogens.
• Proteins are the most potent immunogens, with polysaccharides
ranking second.
• Humoral immunity experimental studies use proteins or
polysaccharides as immunogens.
• For cell-mediated immunity, only proteins and some lipids and
glycolipids serve as immunogens.
• Proteins must first be processed into small peptides and then
presented together with MHC molecules on the membrane of a cell
before they can be recognized as immunogens.
27. Factors Influencing Immunogenicity
Immunogenicity is not an intrinsic property of an
antigen but rather depends on a number of properties
of the particular biological system that the antigen
encounters
• The factors includes:
i. The Nature of the Immunogen
ii. The Biological System
iii. Mode of administration
28. I. Nature of the Immunogen
Foreignness:
• In order to elicit an immune response, a molecule must be
recognized as non-self by the biological system.
• The capacity to recognize nonself is accompanied by
tolerance of self, a specific unresponsiveness to self
antigens.
Molecular size:
• The most potent immunogens are usually large proteins, have a
molecular mass > 10,000Da
• Generally, substances with a molecular mass less than 5000 Da are
poor immunogens.
• And very small ones (e.g, amino acids, Haptens) are non immunogenic
29. Chemical nature and composition:
• In general the more complex the substance is chemically the more
immunogenic it will be
• Immunogenicity Order;
Proteins > carbohydrates > lipid > nucleic acids.
Structural complexity:
• Simple homopolymers made up of single amino acid lack
immunogenicity.
• Polymers made up of two or more amino acids are immunogenic.
• Addition of aromatic amino acids increases immunogenicity.
Antigen specificity:
• Antigen specificity depends on the specific active sites on the
antigenic molecule
30. Degradability:
• Antigens that are easily phagocytosed are generally more
immunogenic
• Macromolecules that cannot be degraded and presented
with MHC molecules are poor immunogens.
Auto specificity:
• Autologous or self antigens are ordinarily not
immunogenic but under certain circumstances may act as
auto antigens
31. II. The biological system
Species Specificity:
• Tissues of all individuals in a particular species
possess species specific antigens
• Human blood group proteins can be differentiated
from animal protein by specific antigen-antibody
reactions
Organ specificity:
• Organ specific Antigens are confined to a
particular organ/tissue
32. Genetic factors:
• The genetic constitution (genotype) of host influences the type and
degree of immune response.
• Different individuals of a given species show different types of
immune responses towards the same antigen.
• Responders- are the individuals who produce antibody faster
• Slow responders- are the individuals who produce antibody
slowly and may need repeated antigenic exposures
• Non-responders - are the individuals who do not produce
antibody in spite of repeated antigenic exposures.
• MHC gene products which present processed antigen to T cells
play a central role in determining the degree of host immune
response to immunogen
33. Age:
• Usually the very young and the very old
individuals have a diminished ability to elicit an
immune response due to weak immune system as
in children immune system is still in
development and in old there is reduced
production of B and T cells in the bone marrow
and thymus and diminished function of mature
lymphocytes in secondary lymphoid tissues.
34. III. Mode of administration
Dose of the antigen:
• Optimal dose is required to stimulate host immune
response
• Achieved by repeated administration or boosters over a
period of weeks
• A single dose of immunogen (under dose) may not induce
a strong response.
Route of administration:
• Parenteral route & Intraperitoneal are preferred over oral.
• Combination of optimal dosage and route of administration will
induce a peak immune response in a given host.
35. Adjuvants:
• Adjuvants are substances that stimulate the immune response by
facilitating uptake into APCs
• Adjuvants are often used to boost the immune response when an
antigen has low immunogenicity or when only small amounts of
an antigen are available.
36. Haptens
• Haptens are small organic
molecules that are antigenic
but not immunogenic by
itself.
• Chemical coupling of a
hapten to a large protein,
called a carrier, yields an
immunogenic hapten-carrier
conjugate which produce
antibodies specific for
(immunogens)
• A hapten-carrier conjugate
contains multiple copies of
the hapten
37. Why knowing Haptens important
• Many biologically important substances, including drugs, peptide
hormones, and steroid hormones, can function as haptens.
• Conjugates of these haptens with large protein carriers produce
hapten-specific antibodies useful for measuring the presence of
various substances in the body
• Formation of drug-protein conjugates in the body can produce
drug allergies that may be life-threatening.
39. References
• TEXTBOOK: JONATHAN M. AUSTYN AND KATHRYN J. WOOD
Principles of Cellular and Molecular Immunology .Chapter 2. pg 63-84.
• TEXTBOOK: ABUL K. ABBAS. ANDREW H. LICHTMAN. CELLULAR AND
MOLECULAR IMMUNOLOGY. 5TH EDITION. pg 58, 216, 489.
• Prescott Harley Microbiology 5th Edition
• Medical Microbiology Patrick Murray 9th Edition,2023
• Immunology by Tapasya Srivastava and Subrata Sinha
• Online Microbiology notes, Antigen Properties, Types and
determinants of Antigenicity
• Immunobiology jenways 10th ed,2023
Editor's Notes
Most antigens are either proteins or polysaccharides.
Lipids and nucleic acid are usually antigen when combine with protein or polysaccharides
The epitopes on an antigen can be linear (i.e., continuous within the amino acid sequence) or conformational (i.e., created by aa residue in diff part of polypeptide chain)
TCR recognize only linear epitope
Conformational epitopes are less obvious and more patentable than linear epitopes.
T cell epitopes are usually protein antigen-derived peptides presented by MHC molecules on antigen-presenting cells and recognized by T-cell receptors.
epitopes are central to vaccine design, infectious disease prevention, disease diagnosis and treatment.
Internal epitopes are
Composed of hydrophilic amino acids on the antigen surface accessible to membrane-bound or free antibody.
They are proteins, polysaccharides, lipids in nature
B cell recognizes soluble antigen t cell can not
Traditional development of live-attenuated- or inactivated whole organisms or toxins which are safer, less reactogenic vaccines and capable of inducing strong immune response, hence adjuvants are designed to improve poorly immunogenic vaccines.
Adjuvants - Extend the presence of antigen in the blood
Alloantigen -These are the antigens derived from other members of the same species of the host, but not from the host itself.
Autologues – self antgn with no ir
Xenoantigen - Found in more than one species eg;
Exotoxin both G+ve bacteria and G-ve.
Toxoid: Exotoxin that loses its toxicity but maintains its antigenicity under suitable conditions (low conc of formaldehyde)
E.g tetanus toxoid, diphtheria toxoid
SYSTEMIC LUPUS ERYTHEMATOSUS
Polycln actv: Antigen that induce proliferation and differentiation of antibody secreting cells from diff B cell
Clones of multiple B cells react to same antigen
Examples T indpnd antigens
Pneumococcal polysaccharide, lipopolysaccharide
Flagella
Affinity maturity- process by which antibody gains increase in affinity, avidity and anti pathogen activity
Complex haptens: -Contain two or more epitopes (multivalent).
Simple haptens: -Contain only one epitope (univalent).
Examples of carrier molecules may be albumins, globulins, or synthetic polypeptides.