Antigens Where we’re going- Immunogenicity vs antigenicity What makes for a good immunogen Haptens Pattern recognition receptors

Aulanni’am Biochemistry Laboratory Faculty of Sciences_UB Antigens Aulanni’am Biochemistry Laboratory Faculty of Sciences_UB

Some definitions: Immunogenicity Immunogen, for practical purposes= antigen Antigenicity- 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 proteins Complexity- homopolymers poor, heteropolymers better Easily 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 persistence Inflammatory- dead Mycobacterium Non-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.

Haptens Haptens 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 do B-cell epitopes and T cell epitopes- differences and why Haptens, and practical applications Toll-like receptors- examples of what they recognize, types of response.