1. Adaptive Immunity  Response occurs within days of the infection  Highly specific  Highly diverse  Memory component  Major cell types involved: T cells, B cells and antigen presenting cells

2. Antigens and Antibodies (CH4)  Antigen – any substance that binds specifically to an antibody or a T cell receptor (TCR).  Antibody- a protein (immunoglobulin) that recognizes a specific region (component) of an antigen. Naïve B cells – membrane-bound Activated B cells (plasma cells) – soluble (have been secreted)  Immunogen- a substance capable of eliciting an immune response.

3. Epitope  Epitope – portion of an antigen that reacts with an antibody or T cell receptor (TCR) also known as an antigenic determinant.

4. Properties of immunogenicity  Foreignness – molecule must be recognized as foreign. tolerance – unresponsiveness to self antigens.

5. Properties of immunogenicity  Molecular size –correlation between size an immunogenicity. Bigger is better – i.e. macromolecules  Chemical composition/complexity

6. Properties of immunogenicity  Processing and presentation – important for T cell responses, ability of the antigen to be phagocytosed and processed.  Large  Insoluble  Aggregates

7. Immunogenicity  Immunogenicity also depends on:  Host factors  Dosage  Route of entry

8. Recall: Jerne, Talmadge & Burnet – clonal selection theory

9. Antibody Structure

10. Antibody-Mediated Effector Functions  Opsonization – promotion of phyagocytosis of antigens by macrophages and neutrophils. Fc receptor (FcR) Metzger 1994

11. Antibody-Mediated Effector Functions  Activate and assist complement system

12. Antibody Classes  Immunoglobulin G (IgG)  Most abundant class  Four subclasses  Activate complement system

13. Antibody Classes  Immunoglobulin M (IgM)  Pentamer  1 st class produced in response to an antigen  Activates complement system

14. Antibody Classes  Immunoglobulin A (IgA)  Predominant class in secretions  Secretory IgA

15. Antibody Classes  Immunoglobulin E (IgE)  Hypersensitivity reactions

16. Antibody Classes  Immunoglobulin D (IgD)  Major membrane-bound immunoglobulin expressed by mature B cells.

17. Antigenic determinants on immunoglobulins  Isotype  Allotype  Idiotype