what is the relationship between antigens and immunogens?
All immunogens are antigens, but not all antigens are immunogens
what is an epitope?
the region(s) of the antigen in direct contact with the antibody, B-Cell Receptor, or T-Cell Receptor
what is a hapten?
a small molecule which can function as an antigen, but by itself is incapable of inducing an immune response
what are the 3 types of antigen/immunogen receptor molecules?
1. BCR (b cell receptor)
2. TCR (t cell receptor)
of the 3 types of antigen/immunogen receptor molecules, which are surface immunoglobulins?
which of the 3 types of antigen/immunogen receptor molecules is expressed on antigen presenting molecules?
which various antigens or sources of antigens are immunogens?
2. foreign proteins
antigens are big molecules- however, the area that triggers the specific immunity is a small part, known as what?
what is the difference between a linear and conformational epitope?
in a conformational epitope, the sequence of amino acids is discontinuous, but they are brought into proximity by the protein's 3-D structure
when is there cross-reaction between different antigens?
when a different antigen has one identical determinant or a similar determinant
what makes a good antigen/immunogen?
1. physical size : > --> better
2. complexity: chemical composition and structural complexity
3. solubility or degradability by antigen processing cells, macrophages, dendritic cells and B cells
4. foreignness to the individual
How do the categories of chemical compounds rank in terms of their immunogenicity based on complexity in descending order?
1. proteins and glycoproteins
3. nucleic acids, phospholipids
how complex are proteins and glycoproteins in terms of their immunogenicity?
complex in composition and structure
how complex are polysaccharides in terms of their immunogenicity?
repeating structures, generally low affinity
do polysaccharides stimulate a cell-mediated immune response?
cannot be processed and presented as linear epitopes for T cells, thus do not induce cell-mediated response
how foreign are nucleic acids and phospholipids in terms of their immunogenicity?
evolutionarily conserved; less foreign
how do nucleic acids and phospholipids become better immunogens?
conjugation with proteins or polysaccharides
what types of drugs can act like haptens and be associated with severe, life threatening anaphylactic reactions?
antibiotics, particularly penicillins
how do penicillins act as haptens?
they form covalent bonds with proteins to produce protein-drug adducts that elicit an immune response (hypersensitivities) in some individuals
what are the 3 types of epitopes in a hapten-conjugate complex?
1. the pure hapten
2. the pure antigen
3. the hapten-antigen complex
do identical twins recognize each other's proteins as foreign?
they have the same genetic makeup and their immune systems would recognize eachother as self
what are examples of immunologically privileged anatomical sites (sequestration)?
corneal, spermatic, CNS cell antigens
What are the types of antigens?
3. T cell independent
4. T cell dependent
what effect do superantigens have on the immune system?
cause hyper activation of the immune system
what does an antigen being T cell independent vs. T cell dependent depend on?
whether an anigen can stimulate B lymphocytes with or without the help from T lymphocytes
How do superantigens induce activation of multiple types of T cells?
they are polyclonal stimulators of T cells, binding to the MHC-TCRβ (on the outside of the polypeptide of TCR) complex, without regard for antigen specificity
what is the result of a superantigen activating up to 20% of circulating CD4 T cells?
massive production of cytokines such as IL1, IL2, and TNFα which causes systemic shock
what are examples of conditions that are caused by superantigens?
toxic shock syndrome
what microbes cause food poisoning and/or toxic shock syndrome?
staphylococcal toxic shock toxin
staphylococcal exfoliating toxin
streptococcal pyrogenic exotoxins
what are T-independent antigens?
antigens which can directly stimulate B cells to produce antibody without the requirement for T cell help
usually, T independent antigens are what?
mitogen and are resistant to degradation by antigen presenting cell
what are examples of T independent antigens?
what are T dependent antigens?
antigens that require the help of T lymphocytes to activate be cells to produce antibody
in addition to size, molecular complexity and foreignness, immunogenicity of an antigen depends on what?
1. physical form
which physical form of an antigen is more immunogenic, particulate or soluble?
particulate > soluble
why are particulate antigens more immunogenic than soluble ones?
particulate form are more easily taken up by antigen presenting cells
what are the relative immunogenicities of routes of administration?
subcutaneous > intraperitoneal > intravenous > intragastric
what is the limitation of the oral route of administration's immunogenicity?
oral route induces local mucosal immunity but not systemic immunity
what is high zone tolerance?
very high doses of antigen inhibit immune responsiveness to a subsequent challenge
what is the effect of an adjuvant on immunogenicity?
substances mixed together with an antigen and enhance an immune response to an antigen
what is the difference between an adjuvant and a carrier molecule?
unlike carrier molecule an adjuvant does not form stable linkage with the antigen
what is an example of an adjuvant?
1. complete Freund's adjuvant
2. aluminum hydroxide/aluminum phosphate
how does an adjuvant increase immunogenicity of an antigen?
1. insolubilize antigen for better phagocyte uptake
2. insolubilize antigen for gradual release over time in lipid emulsions called liposomes with delayed time release of antigen
3. stimulating the influx of phagocytic cells or other immune cells to the site