Antigens Flashcards
The immune response of lymphocytes is triggered by materials called_______
immunogens
macromolecules capable of triggering an adaptive immune response by inducing the formation of antibodies or sensitized T cells in an immuno-competent host.
Immunogens
Immunogens can then specifically react with such…
antibodies or sensitized T cells
The term____ refers to a substance that reacts with antibody or sensitized T cells but may not be able to evoke an immune response in the first place.
antigen
older individuals are…
At the other end of the age scale, neonates…
more likely to have a decreased response to antigenic stimulation.
do not fully respond to immunogens, because their immune systems are not completely developed.
________plays a role, as individuals who are malnourished, fatigued, or stressed are less likely to mount a successful immune response.
Overall health
There appears to be a _______for each individual immunogen.
This allows the innate immune response to take care of small amounts of pathogens and leave the adaptive response for pathogens that are present in large numbers.
threshold dose
Generally, the larger the dose of an immungen one is exposed to, the______ the immune response is.
However, very large doses can result in________, a phenomenon that is not well understood. It is possible that memory cells become overwhelmed and therefore nonresponsive.’
greater
T- and B-cell tolerance
The actual amount of immunogen needed to generate an immune response differs with the…
route of inoculation.
route of inoculation
Such routes include (4) Where the immunogen enters the body determines which cell populations will be involved in the response and how much is needed to trigger a response.
intravenous (into a vein)
intradermal (into the skin)
subcutaneous beneath the skin)
oral administration
________may be involved that allows individuals to respond to particular immunogens.
This predisposition is linked to the MHC and to the receptors generated during T and B lymphocyte development.
genetic predisposition
In general, the ability of an immunogen to stimulate a host response depends on the following characteristics:
TRAITS OF IMMUNOGENS
(1) macromolecular size
(2) chemical composition and molecular complexity
(3) foreignness
(4) the ability to be processed and presented with MHC molecules
Usually an immunogen must have a molecular weight of at least______ to be recognized by the immune system, and the best immunogens typically have a molecular weight of_______
However, there are exceptions, because a few substances with a molecular weight of ______have been known to induce an immune response.
10,000
over 100,000 daltons
less than 1000
The rule of thumb is that the greater the molecular weight…
the more potent the molecule is as an immunogen
Immunogenicity is also determined by a substance’s chemical composition and molecular complexity.
_______are the best immunogens.
Proteins and polysaccharides
are powerful immunogens, because they are made up of a variety of units known as amino acids.
Proteins
Because of the variations in subunits,_______ may have an enormous variety of three-dimensional shapes.
B cells recognize structures that project from the external surfaces of macromolecules, and the more complexity or branching there is, the easier it is for B cells to respond.
proteins
_______ have epitopes that also stimulate T cells, which is essential to generating T-cell help in antibody pro-duction.
In contrast,______ such as nylon or Teflon are made up of a few simple repeating units with no bending or folding within the molecule, and these materials are_______. For this reason, they are used in making artificial heart valves, elbow replacements, and other medical appliances.
Proteins
synthetic polymers; nonimmunogenic
are somewhat less immunogenic than protein, because the units of sugars are more limited than the number of amino acids in protein.
Carbohydrates
As immunogens, carbohydrates most often occur in the form of____ or_____
Many of the blood group antigens are comprised of such carbohydrate complexes.
For example, the A, B, and H blood group antigens are_______, and the Rh and Lewis antigens are________.’
glycolipids or glycoproteins
glycolipids
glycoproteins
_________ and________ are not immunogenic by themselves, although a response can be generated when they are attached to a suitable carrier molecule.
This is the case for autoantibodies to DNA that are formed in systemic lupus erythematosus.
These autoantibodies are actually stimulated by a DNA-protein complex rather than by DNA itself.
Pure nucleic acids and lipids
Another characteristic that all immunogens share is________.
The immune system is normally able to distinguish between self and nonself, and those substances recognized as nonself are______.
foreignness
immunogenic
Any lymphocyte capable of reacting with self-antigen is normally______.
Typically, the more distant_____ the source of the immunogen is from the host, the better it is as a stimulus.
For example, plant protein is a better immuno-gen for an animal than is material from a related animal.
Occasionally, however, autoantibodies, or antibodies to self-antigens, exist.
eliminated
taxonomically
F a substance to elicit an immune response, it must be subject to______, which involes enzymatic digestion to create small peptides or pieces that can be complexed to MHC molecules to present to responsive lymphocytes.
antigen processing
If a macromolecule can’t be degraded and presented with MHC molecules, then it would be a_______.
The particular MHC molecules produced also determine responsiveness to individual antigens.
poor immunogen
Immunogens:
Macromolecules that induce the formation of antibodies or sensitized T cells in an immunocompetent host.
• Antigens:
Substances that react with antibodies or sensitized T cells but may not evoke an immune response initially.
Rule of thumb in immunogen-antigen
“All Immunogens are Antigens, but not all antigens are immunogens.”
Examples of immunogens
Bacteria
Viruses
Fungi
Parasites
Example of antigens
RBCs
______ regions of antibodies will bind with the antigens
Fab region
PAMPs are…
Epitopes
Are small molecules that are antigenic but not immunogenic by themselves.
HAPTEN
HAPTEN
are small molecules that
are antigenic but not immunogenic by themselves.
Why are haptens not consisdered as immunogens/ will not elicit immune response? What do they need, to be considered as an immunogens?
They are so small that out body wouldn’t elicit an immune response.
Low molecular weight particles that can bind to an antibody but must be attached to a macromolecule as a carrier to stimulate a specific immune response
Once it bind with a carrier proteins, it give it an impression that they are bigger thus the body will now elicit an immune response
Haptens are nonimmunogenic materials that, when combined with a carrier, create new antigenic determinants that is recognized by the body as immunogenic.
What will happen in the next exposure to a hapten?
Once the body starts making antibodies, a hapten (a small molecule) can react with these antibodies even if it’s not attached to a larger carrier molecule. However, because the hapten is so small and has only one binding site, it can’t link multiple antibodies together. This means it won’t cause clumping or precipitating reactions, which require cross-linking between antibodies.
______indicates the presence of that particular antigen.
Agglutination
is the process by which particulate antigens such as cells aggregate to form larger complexes when a specific antibody is present.
Agglutination
Poison ivy (Rhus radicans) contains chemical substances called______, which are haptens.
Once in contact with the skin, these can couple with tissue proteins to form the immunogens that give rise to contact dermatitis.
catechols
During the first exposure to poison ivy, the body gets sensitized but usually doesn’t react.
On the second exposure, the immune system recognizes the hapten (urushiol) and mounts a strong reaction, resulting in the familiar rash and itching.
Epitope vs Paratope
Epitope: The specific part of the antigen that is recognized by the antibody.
Paratope: The specific part of the
antibody that recognizes and binds to the epitope
Epitope are also known as
Determinant sites
are molecular shapes or configurations on antigens that are recognized by B cells or T cells.
Epitope
they dictate the specificity of the immune response.
Epitope
These epitopes consist of a continuous sequence of amino acids on a single polypeptide chain.
LINEAR EPITOPE
They result from the three-dimensional folding of a polypeptide chain, bringing amino acids from different parts of the linear sequence into close proximity.
CONFORMATIONAL EPITOPE
CLASSIFICATION: BASED ON AMINO ACID SEQUENCE
EPITOPE
Linear epitope
Conformational epitope
Univalent, unideter minant antigen (hapten)
A-anti-A complexes [not cross-linked)
Unideterminant, multivalent antigen
A-anti-A cross-linked complexes
Multideterminant, multivalent antigen
A-anti-A, B-anti-B, Canti-C cross-linked complexes
Unideterminant
Unideterminant - 1 type of antigen
Univalent - one binding site
FACTORS CONTRIBUTING TO IMMUNOGENICITY
- Factors related to the antigens
- Factors related to the host
- Factors related to the exposure
Factors related to the antigens
Foreignness
Degradability
Molecular weight
Structural stability
Chemical composition & Molecular complexity
Factors related to the host
Ag
Genetic predisposition
Overall health
Factors related to the exposure
Dose
Route of inoculation
The degree to which antigenic determinants are recognized as non-self by an individual’s immune system.
FOREIGNESS
The immune system has evolved to differentiate between self and non-self.
FOREIGNESS
The more foreign the antigen is…
The more the body will elicit an immune response
Why do we avoid transplanting organs from other species
Transplants from other species are usually avoided because the immune system recognizes the antigens as extremely foreign and attacks them aggressively, leading to rejection of the transplant.
We get organs or blood from the same species because the antigens are more similar to our own, making them less likely to trigger a strong immune response, which helps the transplant or transfusion succeed.
• “self” antigens; originate from the host’s own body
Less risk
Autologous
• derived from a genetically identical individual, such as an identical twin
Syngeneic/Isogenic
• from a genetically different member of the same species
Allogenic/Homologous
from a different species, such as animal tissues or organs
Xenogenic/Heterologous
Explain syngeneic in the example of identical twins
In the case of identical twins, a syngeneic transplant involves little to no risk of rejection because their immune systems recognize the transplanted organ as “self” due to their identical genetic makeup.
Explain autologous and give example
In nose surgery, using autologous tissue (like cartilage from your own body) eliminates the risk of rejection and reduces complications, making the procedure safer and more effective.
Explain allogenic and give example
In an allogenic transplant, tissues or organs are taken from one person and given to another person of the same species. Because the donor and recipient are not genetically identical, there is a risk of rejection, which is managed by matching as closely as possible and using immunosuppressive drugs.
Explain xenogenic and give example
In xenogenic treatments like using tilapia skin for burns, tissues from a different species are used in humans. The tilapia skin helps in wound healing and protection but may pose risks of immune reactions, which are managed through processing and careful application.
• A phenomenon where an antibody generated against one antigen can also bind to a similar, but distinct, antigen
Cross-reactivity
For an antigen to be recognized as foreign, it must be processed and presented to immune cells in a recognizable form.
This processing often involves the breakdown or degradation of the immunogen into smaller fragments that can be displayed on MHC molecules for recognition by T cells.
DEGRADABILITY
Importance of degradability
Degradability is crucial for antigens because it allows the immune system to process and present them properly, helps in clearing them from the body, and contributes to effective vaccine design
What if antigen is too big or hard to degrade?
If an antigen is too big or hard to degrade, it can impair the immune system’s ability to process it, potentially leading to ineffective immune responses, chronic inflammation, or complications in vaccine development.
The more the antigen is easy to degrade…
The more immunogenic it is
MOLECULAR WEIGHT (MW)
Generally, larger molecules…
are more immunogenic.
MW of_______ = recognizable by the immune system
________ = most potent immunogens
10,000 daltons
> 100,000 daltons
allows the immunogen to persist within the host’s body for a sufficient duration, giving the immune system adequate time to mount an effective response.
Conversely, unstable molecules are quickly degraded and cleared, limiting their ability to elicit a sustained immune reaction.
STRUCTURAL STABILITY
The stable the antigen is….
The more it can elicit an immune response
Stable-> stays longer in the body-> more time to learn and study the antigen-> easier to kill next time
Adjuvants in the vaccine
Adjuvants are added to vaccines to improve the strength and duration of the immune response, allowing for more effective protection against diseases.
They help enhance the vaccine’s effectiveness, often reducing the amount of antigen needed and the number of doses required.
How does adjuvants increase the efficacy of vaccines
Adjuvants enhance vaccine efficacy by boosting the immune system’s response to the antigen, prolonging the presence of the antigen, improving antigen presentation, allowing for lower doses of antigen, and stimulating multiple immune pathways.
These actions help ensure a stronger and more durable immune protection.
- substances that, when administered alongside an immunogen, enhance the
immune response to that immunogen.
Adjuvants
Adjuvants increase IR by….?
• Enhancing antigen uptake
• Increasing APC accumulation
• Stimulating costimulatory molecules
• Inducing cytokine release
Complex molecules, with a higher diversity of antigenic determinants or epitopes, are….
more likely to be recognized by the immune system and elicit a response.
are highly immunogenic.
Proteins
Simpler molecules like____, _____, and _____, though capable of acting as antigens, are generally less immunogenic.
lipids, carbohydrates, and nucleic acids
are highly antigenic because of their large size and complex structures
Proteins
are less antigenic but can elicit immune responses when bound to proteins or lipids
Carbohydrates
are weakly antigenic on their own but can become more antigenic when conjugated to larger molecules.
• Nucleic acids and lipids
AGE
•_______ tend to have a diminished response to antigenic stimulation
•______’ immune systems are not fully developed, leading to a weaker response to immunogens.
Older individuals
Neonates
GENETIC PREDISPOSITION
•_________ are responsible for presenting antigens to T cells, a critical step in initiating both humoral and cellular immunity.
• Variations in_____ genes can affect an individual’s ability to respond to specific immunogens.
MHC molecules
Highest form of immunogen
Protein
Deterioration of thymus
Thymic involution
OVERALL HEALTH
Individuals facing ___________,are less likely to mount а successful immune
response.
malnutrition, fatigue, or stress
______ is required to generate a response varies depending on the immunogen and the individual.
DOSE OF IMMUNOGEN
Importance of dose of Immunogen in eliciting an immune response
The dose of an immunogen is vital for inducing a strong and effective immune response. It needs to be high enough to activate the immune system and ensure proper antigen presentation and immune memory, while avoiding too low a dose that could lead to a weak response or too high a dose that could cause side effects
Salmonella vs Shigella
Shigella requires a higher dose to be infected while salmonella only needs a small those
ROUTE OF INOCULATION
“ Different routes, such as ____________ activate different cell populations and pathways within the immune system.
intravenous
intradermal
subcutaneous
oral
This highlights the importance of administering vaccines and medications through the appropriate route for optimal effectiveness.
ROUTE OF INOCULATION
Importance of administering vaccines or medication in proper locations
The route of inoculation (how a vaccine or medication is given) is crucial for its effectiveness.
It affects where the treatment works best, how quickly it acts, how well it’s absorbed, how it minimizes side effects, and how convenient it is for the patient.
Choosing the right route ensures the treatment works well and is as effective as possible.
