The Immune System

1. The Immune System (Chapter 43) Raj Patel AP Biology 4/27/12

2. What Is It? • The Immune System is designed to help protect the human body from outside threats • These threats include viruses, bacteria, and other pathogens • There are two types of immunity defense: Innate Immunity and Acquired Immunity.

3. Innate Immunity • Present at start of birth and provides broad defense • Has both external and internal defenses:

4. External Defenses • 1) Skin = barrier that is hard to penetrate • 2) Mucous membranes = digestive and respiratory tract linings that make mucus (traps microbes) • 3) Secretions = saliva, tears, etc. Has lysozymes that digest bacterial cell walls. (1) (2) (3)

5. Internal Defenses • 1) Phagocytes = attach to bacteria’s surface polysaccharide receptors  form lysosome vacuoles  engulf bacteria • Types: • Neutrophils enter bacteria site and then engulf, but then self-destruct • Macrophages reside in lymphatic tissue and capture bacteria via netlike extensions • Eosinophils discharge destructive enzymes • Dendritic cells can also engulf bacteria

6. Internal Defenses • 2) Antimicrobial proteins = impede microbe reproduction through interferons • 3) Natural Killer cells = kill virus-infected/cancer cells by releasing chemicals that cause apoptosis (programmed cell death) • 4) Inflammatory response = histamine chemical increases blood flow to bacteria site and helps clot

7. Acquired Immunity • Main proteins are cytokines, which help activate other cells in the immune system (reaction pathway) • Antigen = any molecule that elicits a response from cytokines • Epitope = portion of antigen that cytokines can bind onto in order to recognize molecule

8. Acquired Immunity • 2 Types of lymphocytes: 1) B lymphocytes (B cells) – receptors for antigens are Y- shaped and have 4 polypeptide chains (2 heavy and 2 light). 2) T lymphocytes (T cells) – receptors for antigens have 2 polypeptide chains, α chain and β chain, attached by disulfide bridge • MHC (major histocompatibility complex) attach to antigen and are recognized by T cells.  Class I MHC = found on all cells; bind peptides derived from foreign antigens that are synthesized in the cell  Class II MHC = bind peptides from foreign antigens that are fragmented, or broken, from phagocytosis/endocytosis

9. Lymphocyte Development • Lymphocytes arise from stem cells in the bone marrow • B cells develop entirely in bone marrow • T cells develop in thymus

10. Lymphocyte Diversity • Nearly impossible for two B cells to have same exact receptors (same for T cells) • Each person has 1 million different B cells and 10 million different T cells • Differentiation is a result of random gene rearrangements in mRNA sequences

11. Gene Rearrangements

12. Clonal Selection of Lymphocytes • When an antigen selects a B or T cell, the stimulated lymphocyte divides into 2 clone daughter cells • 1st clone is made of many effector cells that combat the same antigen (short-lived) • 2nd clone is made of memory cells that have receptors for specific antigens (long-lived)

13. Clonal Selection of Lymphocytes • Clonal Selection – antigen driven cloning of lymphocytes; consists of the steps: • Primary Immune Response – peaks after 10-17 days after initial exposure to antigen. Plasma cells (secrete antibodies) are made. • Secondary Immune Response – peaks after only 2-7 days after secondary exposure. This response is faster, stronger, and longer.

14. Humoral/Cell-Mediated Immunity • Acquired immunity is separated into 2 main branches: humoral immune response and cell-mediated response. • Humoral defends against pathogens toxins. • Cell-mediated defends against infected cells, cancer cells, and tissues.

15. T Cells • Helper T Cells – when it recognizes an antigen, it separates into clones and secrete cytokines that stimulate nearby lymphocytes. • Cytotoxic T Cells – uses a surface protein CD8 that keeps the binding between antigen and T cell strong. Used against cancer/infected cells. LINK A Overview of the Immune System and Its Cells

16. B Cells • B Cells differentiate into a clone plasma cell and a clone memory B cell once stimulated. • Once finished, the B cell sends the fragmented remains of the antigen to a helper T cell to finish off.

17. Antibody Classes • There are 5 main types of antibody classes:

18. Active and Passive Immunity • Active immunity – immunity response that is triggered by exposure to an infectious molecule. Immunization (Vaccination) - develops prior to an active immunity response and depends on a cell’s memory of the antigen. • Passive immunity – immunity response that is triggered when antibodies from an immune person is transferred to someone who is not.

19. Blood Groups and Transfusions How Do They Work? • TypeA blood cells have the A antigen on the surface • TypeB blood cells have the B antigen on the surface • TypeAB blood cells have both A and B antigens on the surface • TypeO blood cells have neither on the surface Acceptable Transfusions:

20. Immune Response Side-Effects • Sometimes, responses from the immune system can lead to diseases and conditions that are a result of the response. • Allergies are exaggerated (very sensitive) responses to specific antigens called allergens that trigger the response. • In this case, plasma cells secrete antibodies usually on pollen grains (hence, “spring allergies”). When the pollen grains enter the body again, they induce the cell to release histamine and other inflammatory molecules (called degranulation). • As part of the inflammatory response and increased blood vessel flow, symptoms like sneezing, runny nose, watery eyes, and itchy nose can result. Allergies

21. Autoimmune Diseases • Autoimmune diseases – diseases that are triggered when immune system loses tolerance against itself. • Antibodies targeted against the body’s own natural molecules (histones, DNA breakdown) are released and various diseases can result. • Ex.) Lupus – disease characterized by skin rashes, fever, arthritis, and organ dysfunction.

22. Inborn (Primary) Immunodeficiencies • These deficiencies result from defects in the basic development of immune system cells. Both innate and acquired defenses can be seriously impaired. Acquired (Secondary) Immunodeficiencies • These deficiencies can develop later in life and are caused by some external agent as opposed to natural birth causes. • Serious developments can impair the immune system • Hodgkin’s Disease – damages the lymphatic system • AIDS (Acquired Immunodeficiency Syndrome) – this infamous condition makes infected people severely susceptible to immune system breakdowns even from the most basic coughs, fevers, colds, etc.