Immune System Chapter 43 AP/IB Biology

Importance of the Immune System Defends against foreign invaders (bacteria, fungi, protists, parasites, etc.) Destroys abnormal body cells

Types of Defense Innate Defenses – non- discriminating mechanisms 1st Line – Skin and mucous membranes – prevent entry into body; trap foreign bodies Lysozyme – digests microbial cell walls

2nd Line Phagocytic cells – engulf and destroy foreign bodies

Inflammatory Response Localized response in a damaged area Histamine – released by body cells Blood flow increases to that area Permeability of capillaries increases Phagocytic cells arrive

Natural Killer (NK) cells – recognize infected cells and destroy them Interferons – secreted by virus infected cells (“save yourself” message) Diffuse to neighboring cells and cause them to release other chemicals that inhibit viral production Natural Killer (NK) cells – recognize infected cells and destroy them

Specific Defense – 3rd Line Selective with what is foreign Foreign identified by antigens, molecules found on surfaces that elicit a response by lymphocytes Circulate throughout blood and lymph; concentrated in spleen, lymph nodes and other lymphatic tissue

Lymphocytes Pass antigen receptors (~100,000) on the plasma membrane Receptors are antigen specific (only 1) Body constantly produces varieties of two types of lymphocytes

B Lymphocytes B Cells Originate and mature in stem cells of bone marrow When activated, some can produce antigen specific antibodies – proteins that are attracted to specific antigens Some can become long living memory B cells – able to produce antibodies later in time

T Lymphocytes T Cells Produced in stem cells of bone marrow and mature in the thymus Types include Helper T Cells – recognizes antigen-presenting cells and stimulate B cells and… Cytotoxic T Cells – involved in the destruction of tumor cells, virus- infected cells, or other damaged cells Memory T Cells – long-living cells that can recognize abnormal cells later in time

Recognizing Self from Non-Self The immune system has the ability to recognize what is foreign and what should be present On surface of membranes are molecules that generate a membrane fingerprint (major histocompatibility complex – MHC) Recognized by T cells Antigen fragments are presented in the MHC so that T cells may recognize them

Clonal Selection Immune system generates a wide variety of different B and T cells (different antigen receptors) Only B or T cell with the exact antigen receptor is selected to divide and differentiate Effector cells – short lived; become the cells that fight Memory cells – long lived cells that remain

Humoral Immunity Bacteria and viruses Antigen enters (1st exposure) Free floating antigens activate selected B cells Plasma cells secrete antibodies Memory cells are generated If antigens consumed by macrophage Antigen is presented to Helper T cell can also activate selected B cells

Effect of Antibodies

Cell Mediated Immunity Bacteria, viruses, fungi, protists Antigen enters (1st exposure) Macrophage presents antigen to Helper T cell or displayed by an infected cell Cytotoxic T cells selected and stimulated Active cytotoxic T cells generated (lyse cells) Memory T cells generated

Primary vs. Secondary Immune Response Primary is response from the initial exposure to the antigen 10-17 days required to generate effector cells Symptoms seen Secondary is the response from a following exposure Memory cells react quickly (2-7 days) Slight to no symptoms

Acquiring Immunity Active Immunity Immunization/Vaccination Natural exposure to an antigen Immunization/Vaccination Exposure to inactivated, weakened, or parts of antigens (primary immune response stimulated with little to no symptoms) Passive Immunity Antibodies passed from person to person (breast milk to child)

Problems and Concerns Limits to blood transfusions and tissue transplants ABO Blood Group MHC different, resulting in immune responses Require immune suppressing drugs

Abnormal Immune Function Allergies – exaggerated immune response to harmless antigens; results in large amounts of histamine to be released (on a second exposure to allergen)

Autoimmune Disease – immune system attacks certain molecules in the body that should be recognized as self (rheumatoid arthritis, lupus) Immunodeficiency Disease – aspects of the immune system fail to function Sever Combined Immunodeficiency Syndrome (SCID) – both branches do not work

Acquired Diseases Human Immunodeficiency Virus (HIV) Infect cells with the CD4 marker (primarily helper T cells) Is a retrovirus – uses reverse transcriptase to make DNA from RNA; DNA incorporated into host DNA and new viruses are made