The Immune System Ch th ed Campbell’s Biology

Figure 43.4 The human lymphatic system

Figure 43.1 An overview of the body's defenses

First Line of Defense A barrier that prevents pathogens from entering the body –Nonspecific in nature –Includes: Skin Mucous membranes (which contain lysozyme, an antimicrobial agent) Cilia in respiratory system to sweep out mucus and trapped microbes Stomach acid

Second Line of Defense Nonspecific in nature –Includes: 1. Inflammatory response 1. Inflammatory response Histamine (triggers vasodilation/secreted by basophils and mast cells) Prostaglandins (promote blood flow to area) Chemokines (attracts phagocytes to an infected area) Pyrogens ( body temp to speed up immune system) Pyrogens ( ↑ body temp to speed up immune system)

Figure 43.5 A simplified view of the inflammatory response

2 nd Line of Defense, cont’d 2. Phagocytic Cells Ingest invading microbes Includes monocytes (macrophages) and neutrophils 3. Complement, a group of proteins that help with nonspecific and specific responses 4. Interferons block viral infections 5. Natural killer (NK) cells destroy virus-infected body cells and cancer cells by damaging membranes and causing cells to lyse

3rd Line of Defense Lymphocytes recognize specific antigens while circulating in blood, lymph, and lymphatic tissue B lymphocytes –Made in bone marrow –Mature in bone marrow –Humoral response/produce antibodies –Can secrete 2,000 antibodies/sec over 4-5 days –Stimulated to respond by free viruses, bacterial toxins, or by T lymphocytes

3rd Line of Defense, cont’d T Lymphocytes –Made in bone marrow –Mature in thymus –Cell-mediated response stimulated by cells which present foreign antigens on their surface Two types of T-cells –Cytotoxic T-cells –Helper T cells

Cytotoxic T cells Also called CD8 cells –Kill body cells infected with viruses or other pathogens and cancer cells –Contain antigen receptors on cell surface that bind to protein fragments displayed by class I MHC molecules –Activated T-cell differentiates into plasma cells and memory cells –Kill infected cells by lysing cells with perforin –Infecting microbes then disposed of by circulating antibodies

Helper T-cells Also referred to as CD4 cells –Tell immune system that foreign antigens have entered the body –Bind to class II MHC molecules presenting antigens –Activated T h cells differentiate into plasma cells and memory cells –Stimulate T c cells, B cells, and other T h cells by releasing cytokines and interleukins-1 and 2

MHC Molecules Major Histocompatability Complex = MHC Identify cells as self No two people except identical twins have same MHC markers Class I MHC found on almost all body cells Class II MHC found on specialized cells such as macrophages, B cells, and activated T-cells

Figure 43.9 The interaction of T cells with MHC molecules

Clonal Selection Antigenic molecules bind to specific B or T lymphocytes Selected lymphocytes proliferate and differentiate into plasma or memory cells Plasma cells are short-lived and fight the antigen immediately = primary immune response Memory cells are long-lived cells that can be reactivated = secondary immune response or immunological memory

Figure 43.6 Clonal selection

Figure 43.7 Immunological memory

Antibodies Also called immunoglobulins Y-shaped molecules consisting of 4 polypeptides, 2 identical heavy chains and two identical light chains joined by disulfide bonds 5 Classes –IgM is first circulating antibody to respond (pentamer) –IgG is most abundant of circulating antibodies –IgA is in mucous membranes and in colostrum –IgD –IgE facilitate release of histamine/allergies

Figure Epitopes (antigenic determinants)

Figure 43.15a,b The structure of a typical antibody molecule

How do antibodies work? Form antigen-antibody complex which is phagocytosed by macrophages Complement fixation in which proteins assist in lysing cells by destroying the plasma membrane Antibodies are believed to be made prior to any exposure to antigenic agents.

Figure Effector mechanisms of humoral immunity

Figure The classical complement pathway, resulting in lysis of a target cell

Types of Immunity Passive Immunity –Temporary –IgA or IgG that pass to fetus –Injection of gamma globulin Active Immunity –Make own antibodies or stimulate antibody production via immunization (vaccination)

ABO Antibodies Blood Type O = universal donor Blood Type AB = universal recipient Blood Type AB = universal recipient Blood Type AntigensAntibodies AAB BBA AB A & B none Onone

AIDS Virus HIV attacks cells that bear CD4 molecules on their surface, mainly helper T-cells

Figure The stages of HIV infection

Positive Feedback in the Immune System Seen in activity of helper T-cells Activated T h cells serve to activate more T h cells

Odds & Ends on Immunity Allergens generate hypersensitive immune responses to certain substances Anaphylactic Shock = acute, life-threatening allergic response Antibiotics kill bacteria or fungi NOT viruses Autoimmune diseases –Ex: MS, lupus, arthritis, juvenile diabetes –Body recognizes self as non-self Monoclonal Antibodies –Antibodies produced by a single B cell/important in treatment and diagnosis of certain diseases

Figure Mast cells, IgE, and the allergic response