1. Immune System Basics  Immunity: The capacity to resist infectious pathogens.  Pathogens: Disease-causing organisms  Self vs. Non-self recognition  Major Histocompatibility Complex (MHC 1)  Antigen- a particle or piece of pathogen an immune system recognizes as foreign. MHC 1 Antigens

3. 1st Defense: Non-specific Immune System  Reacts immediately after infection- does not need to ID pathogen. 1.Barrier Defenses: Skin and Mucous membranes 2.Inflammatory Defenses:  Histamine is released at the sign of damage  Blood vessels leak fluid and WBC’s 3.Cellular and Molecular Defenses : 1.Macrophages: Use pocket transport (phagocytosis) to destroy foreign particles. 2.Natural Killer Cells (NK): Release hydrolytic enzymes onto target cells to rupture/destroy them. 3.Interferon 4.Complement  Reacts immediately after infection- does not need to ID pathogen. 1.Barrier Defenses: Skin and Mucous membranes 2.Inflammatory Defenses:  Histamine is released at the sign of damage  Blood vessels leak fluid and WBC’s 3.Cellular and Molecular Defenses : 1.Macrophages: Use pocket transport (phagocytosis) to destroy foreign particles. 2.Natural Killer Cells (NK): Release hydrolytic enzymes onto target cells to rupture/destroy them. 3.Interferon 4.Complement

4. Final Defense: Specific Immune System Recognizes pathogens and develops a sustained immune response. Comprised of two parts: 1.Cell- Mediated Response 2.Humoral Response White blood cells characters (lymphocytes): Helper T cells (T h ) Killer T cells (T c ) B cells Macrophage Recognizes pathogens and develops a sustained immune response. Comprised of two parts: 1.Cell- Mediated Response 2.Humoral Response White blood cells characters (lymphocytes): Helper T cells (T h ) Killer T cells (T c ) B cells Macrophage

5. Specific Immunity- The Battle Begins!  Macrophages search body tissues for pathogens.  Consume pathogens with phagocytosis, kill it with lysosomes, and save the antigens.  Antigens placed into MHC 2 receptors and displayed on macrophage’s membrane.  The macrophage is now considered an antigen-presenting cell (APC).  Macrophages search body tissues for pathogens.  Consume pathogens with phagocytosis, kill it with lysosomes, and save the antigens.  Antigens placed into MHC 2 receptors and displayed on macrophage’s membrane.  The macrophage is now considered an antigen-presenting cell (APC).

6. Specific Immunity Cont.  Macrophage chemically signals Helper T to attach to it.  Helper T attaches to MHC 2 receptor (with foreign antigen stuck in it) with a CD4 receptor.  Helper T cells have incredible variety of receptors that act like a “lock and key” in regards to the displayed antigen.  If the Helper T’s “key” fits the displayed antigen’s “lock”, the Helper T is activated.  Activation results in Helper T releasing cytokines (ex. Interleukin)- chemicals that cause lymphocytes to start mitosis.  Macrophage chemically signals Helper T to attach to it.  Helper T attaches to MHC 2 receptor (with foreign antigen stuck in it) with a CD4 receptor.  Helper T cells have incredible variety of receptors that act like a “lock and key” in regards to the displayed antigen.  If the Helper T’s “key” fits the displayed antigen’s “lock”, the Helper T is activated.  Activation results in Helper T releasing cytokines (ex. Interleukin)- chemicals that cause lymphocytes to start mitosis.

7. Fig. 43-17 Antigen- presenting cell Peptide antigen Cell-mediated immunity (attack on infected cells) Class II MHC molecule CD4 TCR (T cell receptor) Helper T cell Humoral immunity (secretion of antibodies by plasma cells) Cytotoxic T cell Cytokines B cell Bacterium + ++ +

8. Cell-Mediated Response Seek and Destroy  Body cells can be infected by viruses that will hide inside the cell.  As the virus reproduces inside cells, pieces of it fall off and are put into new MHC 1 receptors that the cell puts on its own membrane.  Killer T cells can bind to MHC 1 receptors with their CD8 receptors.  If Killer T binds to MHC 1 receptors with antigen attached, it releases a chemical called perforin.  Perforin ruptures the infected cells membrane and exposes the virus to other immune cells.  Body cells can be infected by viruses that will hide inside the cell.  As the virus reproduces inside cells, pieces of it fall off and are put into new MHC 1 receptors that the cell puts on its own membrane.  Killer T cells can bind to MHC 1 receptors with their CD8 receptors.  If Killer T binds to MHC 1 receptors with antigen attached, it releases a chemical called perforin.  Perforin ruptures the infected cells membrane and exposes the virus to other immune cells.

10. Fig. 43-11 Antigen Top view: binding surface exposed to antigen receptors Plasma membrane of infected cell Antigen Class I MHC molecule

11. Fig. 43-18-3 Cytotoxic T cell Perforin Granzymes TCR CD8 Class I MHC molecule Target cell Peptide antigen Pore Released cytotoxic T cell Dying target cell

12. Fig. 43-12 Infected cell Antigen fragment Class I MHC molecule T cell receptor (a) Antigen associates with MHC molecule T cell recognizes combination Cytotoxic T cell(b)Helper T cell T cell receptor Class II MHC molecule Antigen fragment Antigen- presenting cell Microbe 1 1 1 2 2 2

13. Humoral System Bring in the artillery!  B cells have receptors called antibodies (100,000/cell).  Different B cells have uniquely shaped antibodies that match specific antigens.  If a B cell’s antibody is able to bind with a specific antigen (lock and key effect), the B cell receives a message from Helper T’s to become activated.  Activated B cells divide into Plasma B and Memory B cells.  B cells have receptors called antibodies (100,000/cell).  Different B cells have uniquely shaped antibodies that match specific antigens.  If a B cell’s antibody is able to bind with a specific antigen (lock and key effect), the B cell receives a message from Helper T’s to become activated.  Activated B cells divide into Plasma B and Memory B cells.

14. Humoral System Cont.  Plasma B cells produce and secrete 10,000 “keyed” antibodies per hour.  Due to their shape, each can bind to several antigens at once.  Antigen/Antibody binding has three effects.  Neutralization  Macrophage signaling  Complement pore formation  Plasma B cells produce and secrete 10,000 “keyed” antibodies per hour.  Due to their shape, each can bind to several antigens at once.  Antigen/Antibody binding has three effects.  Neutralization  Macrophage signaling  Complement pore formation

15. Fig. 43-21 Viral neutralization Virus Opsonization Bacterium Macrophage Activation of complement system and pore formation Complement proteins Formation of membrane attack complex Flow of water and ions Pore Foreign cell

16. Memory B cells  These cells do not actively produce antibodies  Instead, they remain in the bloodstream and maintain their cell life cycle independently from T h commands.  If the same pathogen/antigen complex presents itself in the future, these cells are already activated and ready to produce antibodies.  There are also Memory versions of T h and T c cells that serve a similar function.  These cells do not actively produce antibodies  Instead, they remain in the bloodstream and maintain their cell life cycle independently from T h commands.  If the same pathogen/antigen complex presents itself in the future, these cells are already activated and ready to produce antibodies.  There are also Memory versions of T h and T c cells that serve a similar function.