ANTIGENS

Antigen: Any substance reacting with the products of any specific immune response (Ig or T cells)

Immunogen: Any substance capable to induce a specific immune response

All antigens are NOT Immunogenic.

For immunogenicity:- foreign substance

- Cemically more complex- Larger molecules are better immunogens (no limit but

usually > 6000 Da)

Particulate antigens are better immunogens than soluble antigens

Denaturated antigenes are more immunogenic than the native forms

Easly degradable and phagocytosed antigens are more immonogenic

Host genetic factors influence the immunogenceity.

The age of the hosts influence also the immune response

The dose and route of antigen administration also influence the immune response

Antigens can bind to

B cell receptors T cell receptors MHC molecules

Haptens: Small molecules, which are not immunogenic but they induce an immune response when they are attached to a carrier molecule.

Chemically Antigens Can Be

Protein (pure, lipoprotein or glycoproteins)

CH (polysaccharides and lipopolysaccharides)

Nucleic acids* Lipids are not immunogenic but

some phospholipids or glycolipids may stimulate T cells

Antigenic determinant or epitope: the portion of the antigen which binds to the the products of a specific immune response

T dependent antigens

They stimulate antibody production with the aid of T cells.

- Proteins

T independent antigens

They can directly stimulate B cells without the help of T cells

Pollysaccharides (repeated same antigenic sites)

Type 1 T independent antigenes may activate B cells polyclonally, type 2 NOT

Adjuvants: Enhance the biological effects o an antigen, nonspecifically.

Antigenic determinants recognized by B cells

Linear epitopes: 4-8 amino acid or sugar residues

Conformotional epitopes

T cells recognise only amino acid sequences in a protein

T cells recognize peptides asscoiated with MHC

Antigenic determinants are usually 12-22 amino acids long