Lecture 4- Antigens and Haptens Flashcards
What is an antigen?
Any substance (an organism, a molecule, or part of a molecule) that binds to a B cell receptor, antibody, or T cell receptor
[usually foreign]
Antigens have the ability to combine specifically with ______ ______ or sensitized __________
antibodies produced ;
T-lymphocytes
Where do the antigens originate for exogenous and endogenous?
- exogenous - comes from outside
- endogenous - comes from inside
What is an immunogen?
an antigen that induces an immune response
Where are bacterial antigens found?
surface of the cell or flagella
A small molecule that cannot produce an immune response on its own unless combined with a larger carrier, such as a protein, is called what?
hapten
Things “happen everyday but not all things are bad” until combined”
Name 3 features of haptens:
1) small, low molecular weight substances.
2) not immunogenic by themselves
3) they must use a carrier molecule (protein, albumin, globulins) to elicit a response
Give examples of haptans:
Simple chemicals and drugs, like
1. penicillin (PCN)
2. sulphonium (ions attached to sulfur)
3. aspirin (ASA)
4. cosmetics
5. tranquillizers
6. neomycin skin ointment
What is an epitope (antigenic determinant)?
Sites on or within an antigen that antibodies react
Antibodies are specific for ______.
unique structures on a B or T cell
epitopes
The portion of an antigen that is
recognized and bound by an antibody (Ab) or a Tcell receptor (TCR) is called?
epitope
Another name for epitope is?
antigenic determinant
How would you describe a multivalent antigen?
One type of B cell ;
Many epitopes of the same specificity.
How would you describe a polyvalent antigen?
Multiple B cells react because it has many epitopes of different specificities.
Antibodies only recognize _______ epitopes.
native
Do pathogens contain multiple antigens?
Yes
Do antigens contain multiple epitopes?
Yes
What are the types of antigens?
- autoantigens
- transplant
- exogenous
- endogenous
What is allograft?
tissue that is transplanted from a donor to a recipient who is not an identical twin
Which antigens are proteins expressed on the donor tissue that have the capacity to initiate an immune reaction against the allograft?
Transplant
What are the 2 types of human tissue antigens?
Blood group antigens &
Histocompatibility antigens
What are the blood group antigens?
Type A, Type B, Rh, and O+ antigens
What are the 2 histocompatibility antigens?
they are glycoprotein molecules on nucleotide cells that haptens bind to
- Major histocompatibility complex antigens (MHC)
- Human leukocyte antigen (HLA)
Which class is most potent of the MHC?
class I and class 2
Describe the Major Histocompatibility Complex Antigens (MHC)
- A set of cell surface proteins
- Essential for the adaptive immune system
- Recognition of foreign molecules
- Determines histocompatibility (raid rejection of tissue
grafts)
MHC presents to which cells?
T-cells
The helper T cells recognize foreign antigens on the surface of APCs only when they are presented in the ______ of MHC 2 molecules
groove
Cytotoxic T-cells will only recognize antigens, on the surfaces of virus infected cells or tumor cells only when these antigens are presented in the groove of ________ molecules, (MHC _______)
Class I molecule ; restriction
How do exogenous antigens enter the body? 2 types are?
Open surfaces: cuts, nose, mouth, surgery, skin, urethra, etc.
bacterial or viral
What are the 2 types of bacterial antigen classifications?
those related to bacteria cells and those secreted by bacteria
Which antigens are related to bacterial cells?
- Somatic antigen (O): part of cell wall gm –ve bacter.
- Capsular antigen (K): usually polysaccharide
- Flagellar Ag (H) : a protein made of flagellin
- Fimbrial Ag: surface antigens in fimbriated bacilli
What are examples of antigens secreted by bacteria?
exotoxins and enzymes
Describe viral antigens AKA viruses:
- Protein coated viral antigens and
- Soluble antigens (soluble nucleoproteins as in influenza)
What are superantigens (SAgs)?
antigens that activate multiple clones of T-cells, produced by some bacteria and viruses
Give example of superantigens (SAgs):
food poisoning, toxic shock syndrome, rheumatic fever, arthritis, Kawasaki syndrome, atopic dermatitis, and guttate psoriasis
What are some of the bacterial superantigens?
- Staph. aureus- toxic shock syndrome toxin (TSST), and enterotoxins
- Strep. pyogenes - pyrogenic toxin A
Superantigens have the ability to bind to both ______ and _____ .
Class 2 MHC and TCR B chain
Superantigens act as a _______ between the MCH class 2 molecules and beta chain, providing a signal for the T-Cell
clamp
Superantigens are active at very low concentration causing release of large amounts of _________.
cytokines
The massive T-cell activation and release of large amounts of
cytokines cause ________ ________.
systemic toxicity
The method of stimulation of superantigens is NOT _______ for the pathogen.
specific
Superantigens do not lead to an _______ ______, so there is no memory.
acquired immunity
What are substances capable of immunizing the host from which they are obtained?
Autoantigens
Self-antigens are ordinarily ___________.
non-antigenic
___________ of self-antigens are capable of eliciting an immune response.
Modifications
Antigens found within the cytosol of the cell are called?
endogenous antigens
Examples of endogenous antigens?
- viral proteins
- tumor proteins
- intracellular bacteria
_________ is the ability to induce a humoral (antibody) and/or cell-mediated immune response.
Immunogenicity
Immunogenicity can be either _____ or _____ immunogens.
weak or strong
What factors influence immunogenicity?
- How foreign something is
- Molecular size
- Chemical structure
- Route of administration
- Method of administration
Any antigen present only in some of the same species that stimulates antibody production in those that lack the antigen is called?
alloantigen (isoantigen)
Any antigen that occurs in organisms of multiple species is called?
xenoantigen
allos- is the prefix meaning? (Greek origin)
other
xenos- is the prefix meaning? (Greek origin)
stranger
What is a xenograft?
a graft of tissue taken from donor of one species and grafted into the recipient of another species. Ex: pig heart valves in human hearts
T-cells cannot respond to free-floating hapten cells. They must be _____ by the MHC.
processed
Which cells are antigen presenting cells?
B-cells, dendritic cells, MOs
T-cells recognize antigens from what receptors?
Any receptor, (IgG, IgA)
Superantigens do not have to wait for ______ before activating an immunologic response.
a presentation from B-cells or MHC
How does molecular size increase or decrease immunogenicity?
High molecular weight increases immunogenicity.
How does chemical structure effect immunongenicity?
High complexity increase immunogenicity.
Which route of pathogens entering the body has the least effect on immunogenicity?
Oral because stomach acid will kill certain pathogens.
What methods of administration effect immongenicity?
antigen dose and adjuvant (immune response enhancer)
(low dose = low zone tolerance
high dose = high zone tolerance)
How does the adjuvant increase the immunogenicity?
the substance injected with the antigen can enhance the immunogenicity
How does the foreign factor affect immunogenicity?
Tissue from the same species, like allograft, produces a lower immunogenicity than tissue from different species, like xenograft.
What are the B-cell receptor (BCR) features?
- Membrane-bound immunoglobulins (IgM and IgD)
- Secreted in plasma as antibodies.
What are the T-cell receptor (TCR) features?
- There are alpha and beta chains anchored to the T-cells.
- There is a groove that binds small peptides presented by MHC on the surface of APCs.
What is important about MHC molecules?
They are essential for the presentation of peptides so the T-cell can recognize them and bind to them.
What does cross-reactive or heterophile antigens mean?
Heterophile antigens can react with antibodies produced against similar antigens in other species.
Usually different species have different antigen sets, but heterophile antigens mean they are ______ between species.
shared
The epitopes in cross-reactive or heterophile antigens are ______ or very ______.
identical or very similar
(there is a measure of how related the two antigens are)
What immunoglobulin class are heterophile or cross-reactive antibodies?
IgM
What example of cross-reactive antigen is given with Vanguard DA2MP?
This vaccine contains canine distemper (CD), human measles virus, canine adenovirus -2 (CAV-2) and canine parainfluenza (CPI). The measles virus stimulates cross immunity among 6-wk old puppies regardless of the mom’s antibodies that interfere with active CD virus immunization.
What is Onchocerca cervicalis?
parasite that occurs in horses throughout the world, lives in the nuchal ligament in the neck (cervicalis)
Not zoonotic and affects people with O. volvulus, an invasion of the cornea of the eye, AKA “river blindness” from the eggs of black flies
What is moon blindness AKA equine recurrent uveitis (ERU)?
A chronic inflammatory eye disease that affects horses. It is an autoimmune disorder where the body mistakenly attacks the eye tissues.
Treatment aims to reduce inflammation and prevent further damage to the eye. It may include:
1) Corticosteroid eye drops or injections,
2) Immunosuppressant medications
3) Surgery to remove scar tissue or cataracts.
If foreign and self-antigens are similar, why is this bad for the host cell? What is this called?
It is called molecular mimicry ;
Not good for host b/c antigens resemble the host cells → host cells are attacked & targeted.
An anti-hapten antibody CAN bind to _____ hapten or _____ _____ hapten. The molecules are too SMALL for TCRs to see without a presenting molecule.
free hapten ; carrier-bound hapten
What can recognize specific epitopes whether surface-bound, as free soluble molecules, or degraded fragments?
B cell receptors
What receptors can only recognize epitopes when they are bound by MHC molecules?
T cell receptors
What is a hapten-carrier conjugate?
a molecule made by attaching a small chemical group (hapten) to a larger molecule (carrier)
What does the body produce upon the injection of a hapten carrier conjugate?
anti-hapten antibody and anti-carrier antibody
How is antiserum different from antibodies?
antiserum contains different classes of immunoglobulins which may or may not be the target antigen
What is auto-coupling?
Haptens spontaneously forming covalent bonds with host cell proteins or polysaccharides. This results in an allergic phenomena.
Are all antigens immunogens?
Are all immunogens antigens?
No; yes
Adjuvants are considered _______ and are commonly used in __________.
enhancers ; vaccines
What blood types are able to receive type A blood?
A and AB
What blood types are able to receive type B blood?
B and AB
What blood types are able to receive type AB blood?
AB only
What blood types are able to receive type O blood?
Everyone
Only blood types have the Rh protein?
Positive blood types
What recipients cannot receive Rh blood products?
negative
Why can’t positive blood be donated to negative blood?
Negative blood lacks the Rh factor (protein found on blood cell)
Which blood type is the universal donor? universal recipiant?
donor O- ; receive AB+
When would the mother’s antibodies cross the placenta to attack the baby’s blood cells?
On the 2nd pregnancy if she has been exposed to the 1st baby’s blood with a postive RH if she has negative RH on delivery.
What is a tolerogen?
a substance that causes the immune system to be non-responsive to an antigen.
Example RhoGAM
Which type of molecules are most immunogenic?
proteins
What is a superantigen?
A protein that activates T cells in a nonspecific and uncontrolled manner
What molecular weight is considered immunogenic?
> 6000
What happens to the antigen presenting cell of a auto-coupled hapten during an immune response?
both the hapten and the presenting cell die
shoots the messenger
Immunogens contain epitopes that induce a response and is a ______ of the response.
target
Why are polyvalent antigens preferred during vaccinations?
It allows many antibody types to potentially bind to that antigen b/c of the higher number of different epitopes on a single antigen.
When a MHC antigen is presented to a T-cell what happens to the MHC?
MHC restriction (important for the body to reject transplants)
Bacteria can produce an immune response from parts that are related to it. They are?
- Somatic antigen (O) - outer membrane of cell wall
- Capsular antigen (K)
- Flagellar antigen (H)
- Fimbria antigen (Example K88 and K99 fimbriae is an E. coli that causes diarrhea in livestock, specifically pigs and cattle
Theory States: “ A particular antigen dictates the formation of the antigen-binding site on B-cells/antibodies”
What theory is this and why is it incorrect?
Theory: Instructional Theory
Incorrect: An antigen-binding site is already formed before the antigen is stimulated.
Theory States: “Immune cells are ALREADY specific to a specific antigen
What theory is this and why is it incorrect?
Theory: Selective Theory
Incorrect: As we know, the immune cells [B & T] are DIVERSE and become specific after activation via hypermutations
Theory States: “Many clones of a single lymphocytes BEFORE antigen-stimulation”
What theory is this and why is it incorrect?
Theory: Clonal Selection Hypothesis
Incorrect: No, we know that clones are made AFTER antigen-stimulation to enhance specificity
