Antigens
Where we’re going-Immunogenicity vs antigenicityWhat makes for a good immunogenHaptensPattern recognition receptors
Antigens
Aulanni’amBiochemistry Laboratory Faculty of Sciences_UB
Some definitions:
ImmunogenicityImmunogen, for practical
purposes= antigenAntigenicity- ability to react with
antibodies or Tcells; all immunogens are antigens,
but haptens have antigenicity but not immunogenicity.
Immunogen’s contribution- usually think “protein”
Foreignness- Size- > 100 kDa better, < 10 kDa
worse, especially for proteinsComplexity- homopolymers poor,
heteropolymers betterEasily processed better than poorly
processed; adding L-amino acids to a D-polymer increases its immunogenicity.
Genetics- mouse studies- responders and non-responder mice.
Dosage and route of administration- the pneumococcal polysaccharide story.
Route determines which lymph tissues meet the antigen- e.g., spleen vs local lymph nodes.
contribution- adjuvants
Something that stimulates the immune response to the antigen.
Alum- ppt’s, prolongs persistenceInflammatory- dead MycobacteriumNon-specific proliferation of cells- LPS,
Epitopes, or Ag determinants
Our cells don’t react to the whole molecule, but to parts- epitopes
B cells react to differently to epitopes than do T cells.
Remember- interaction is specific!
How B cells do it
An epitope can be non-sequential- 56-62 and 15-21 can be brought together spatially, producing a single epitope.
B cell eptitopes tend to be on the surface,.
How T cells do it
The binding is ternary- three components- MHCII, TCR, antigen. Only parts are displayed.
No MHC binding= no antigenicity
B cell eptitopes tend to be on the surface, but T cells can be from the interior of the molecule.
HaptensHaptens aren’t immunogenic alone.
BUT- when bound to a carrier, Ab’s are produced that DO bind to the unbound hapten
Toll-like Receptors
Recognize bacterial patterns.The response:
– Attraction of phagocytic and Antigen-presenting cells- better at stimulating T cells
– Activation of macrophages– Induction of interferon– Induces secretion of several
cytokines
Summary…
Terms: Immunogen(icity), antigen(icity), hapten
What makes a good antigen?Adjuvants and what they might doB-cell epitopes and T cell epitopes-
differences and whyHaptens, and practical applicationsToll-like receptors- examples of what they
recognize, types of response.