Chapter 24 The Immune System The human body’s immune system recognizes agents that cause disease and attacks them. © 2012 Pearson Education, Inc. 1

INNATE IMMUNITY © 2012 Pearson Education, Inc. 2

24.1 All animals have innate immunity Nearly everything in the environment teems with pathogens, agents that cause disease. The immune system is the body’s system of defenses against agents that cause disease. Innate immunity is a series of defenses that act immediately upon infection and are the same whether or not the pathogen has been encountered before. © 2012 Pearson Education, Inc. 3

24.1 All animals have innate immunity Invertebrates rely solely on innate immunity, which may consist of an exoskeleton, low pH, the enzyme lysozyme, and immune cells capable of phagocytosis, cellular ingestion and digestion of foreign substances. Vertebrates have innate and adaptive immunity. © 2012 Pearson Education, Inc. 4

24.1 All animals have innate immunity Vertebrate innate immunity includes barriers such as skin and mucous membranes, interferons, proteins produced by virus-infected cells, that help to limit the cell-to-cell spread of viruses, neutrophils (phagocytic cells), macrophages, large phagocytic cells that wander through the interstitial fluid, natural killer cells that attack cancer cells and virus-infected cells, and a complement system, a group of about 30 kinds of proteins that can act with other defense mechanisms. © 2012 Pearson Education, Inc. 5

Antiviral proteins block viral reproduction Virus Figure 24.1B Viral nucleic acid Antiviral proteins block viral reproduction Virus 1 New viruses 2 Interferon genes turn on DNA mRNA 3 5 Interferon molecules Interferon stimulates cell to turn on genes for antiviral proteins Figure 24.1B The interferon mechanism against viruses 4 Host cell 1 Host cell 2 Makes interferon; is killed by the virus Is protected against the virus by interferon from cell 1 6

24.2 Inflammation mobilizes the innate immune response Tissue damage triggers the inflammatory response, a major component of our innate immunity, which can disinfect and clean infected tissues and limit the spread of infection to surrounding tissues. Bacterial infections can bring about an overwhelming systemic inflammatory response leading to septic shock, characterized by very high fever and low blood pressure. © 2012 Pearson Education, Inc. 7

Figure 24.2 The inflammatory response Neutrophil Bacteria Splinter Signaling molecules Macrophage Neutrophil Movement of fluid Mast cell Phagocytosis Capillary Red blood cells Figure 24.2 The inflammatory response Neutrophil 1 Tissue injury; signaling molecules are released from mast cells and macrophages that affect capillary cells. 2 Capillaries widen and become leaky. Neutrophils migrate to the infected area. 3 Neutrophils digest bacteria and cell debris at the site, and the tissue heals. 8

ADAPTIVE IMMUNITY © 2012 Pearson Education, Inc. 9

24.3 The adaptive immune response counters specific invaders Our immune system responds to foreign molecules called antigens, which elicit the adaptive immune response. This is a complex biochemical system but essentially lymphocytes produce proteins called antibodies that destroy antigens The adaptive immune system is found only in the vertebrates, reacts to specific pathogens, and “remembers” an invader. © 2012 Pearson Education, Inc. 10

24.3 The adaptive immune response counters specific invaders Infection or vaccination triggers active immunity. Vaccination, or immunization, exposes the immune system to a vaccine, a harmless variant or part of a disease-causing microbe (antigen). Lymphocytes make antibodies that destroy antigens We can temporarily acquire passive immunity by receiving premade antibodies. © 2012 Pearson Education, Inc. 11

24.4 The lymphatic system becomes a crucial battleground during infection The lymphatic system is involved in innate and adaptive immunity and consists of a network of lymphatic vessels, lymph nodes, and lymph, which is similar to blood plasma. Lymph nodes occur throughout the body and include the spleen © 2012 Pearson Education, Inc. 12

24.4 The lymphatic system becomes a crucial battleground during infection Lymphatic vessels collect fluid from body tissues and return it as lymph to the blood. Lymph organs include the spleen and lymph nodes and are packed with white blood cells that fight infections. © 2012 Pearson Education, Inc. 13

24.4 The lymphatic system becomes a crucial battleground during infection As lymph circulates through lymphatic organs it collects microbes, parts of microbes, and microbial toxins, and transports them to lymphatic organs where macrophages in lymphatic organs engulf the invaders and lymphocytes may mount an adaptive immune response by forming antibodies. © 2012 Pearson Education, Inc. 14

Figure 24.4 Organs Adenoid Lymphatic ducts that drain into veins Lymph node Tonsils Lymph nodes Masses of lymphocytes and macrophages Thymus Lymphatic vessels Valve Lymphatic vessel Spleen Blood capillary Tissue cells Interstitial fluid Appendix Bone marrow Figure 24.3 The human lymphatic system Lymphatic capillary 15