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.