1. Adaptive/Acquired Immunity
DENT 516

2. Adaptive immunity
Refers to antigen-specific defense mechanisms that take several days to become protective and are designed to remove a specific antigen. This is the immunity one develops throughout life.
There are two major branches of the adaptive immune responses: humoral immunity and cell-mediated immunity.

3. Cell Mediated Immunity
Humoral Immunity
humoral immunity involves the production of antibody molecules in response to an antigen and is mediated by B-lymphocytes.
Cell Mediated Immunity
CMI involves production of cytotoxic T-lymphocytes,
activated macrophages, activated NK cells and cytokines in response to an antigen and is mediated by T-lymphocytes.

4. Antigens Ags are molecules that elicit an immune response in the body
Ags can be:
Proteins
Polysaccharides
Conjugates of lipids with
Proteins (lipoproteins)
Polysaccharides (glycolipids)

5. Antigens II Ags that enter body from environment include:
Inhaled macromolecules; e.g., cat hair proteins asthma
Ingested macromolecules; e.g. shellfish proteins allergy
Molecules introduced beneath the skin; e.g. splinter, vaccine
Exogenous antigens
Ags generated within the cells of the host:
Proteins encoded by viral genes that have infected a cell
Aberrant proteins that are encoded by mutant genes; e.g. proteins from mutated genes in cancer cells
Endogenous antigens

6. Antigen Presentation
Initial immune response to any Ag requires the Ag be recognized by a T cell.
This is best exemplified by AIDS w/loss of CD4+ T cells.
Two categories of Ags are processed and presented to T cells by different mechanisms:
Exogenous Ags
Endogenous Ags
Dendritic cell
B cell
T cell activated; cytokines released;
Th1, activate M; Th2, activate B cells

7. Exogenous antigens
E. Ag’s (inhaled, ingested, injected), taken up by APCs:
Phagocytic cells; dendritic cells, macrophages
B lymphocytes (produce antibodies)
• APCs
 engulf Ags by endocytosis (endosome-lysosome)
 Ag degraded into short peptides
 peptides displayed at cell surface nestled w/i a class II histocompatibility molecule
 recognized by CD4+ T cells

8. Endogenous Antigens
Ags that are generated w/i a cell; e.g., Mt bug, viral proteins in infected cells
Peptides displayed at cell surface nestled w/I a class I histocompatibility molecule
Recognized by CD8+ T cells
CD8+ T cells are cytotoxic
Have machinery to destroy infected cell
T cell activated; kills infected cell

9. B Lymphocytes: A Special Case
Process Ag by MHC II pathway but:
B cells engulf Ag by receptor mediated endocytosis
BCRs are surface antibodies anchored in plasma membrane
Affinity of BCR for an Ag epitope is so high that the B cell can internalize the Ag at concentrations thousands of times smaller than needed for a macrophage
CD4+ T cell recognizes displayed Ag and is stimulated to release cytokines
These stimulate B cells to grow into a clone of cells; plasma cells
These plasma cells synthesize BCRs with identical binding site for the Ag epitope but w/o the transmembrane tail
The Abs are secreted
release Th2 cytokines

12. Clonal Expansion

13. Types of T cells