Chapter 24 The Immune System

Immune System: Overview Immunity is the body’s ability to protect itself against infectious disease The immune system has three types of components Lymphoid tissues Various types of immune cells Chemical signals that coordinate responses The immune system is able to recognize molecules as foreign (“non-self”) and specifically attack them

Lymphatic System: Introduction The lymphatic system is a vascular system that collects tissue fluid and returns it to the blood. This lymphatic fluid (called lymph) is monitored for pathogens by immune system cells as it travels. (a) Figure 24-2a

Immune System: Functions Protects against pathogens Bacteria Viruses Parasites Protects against foreign molecules (e.g., toxins) Removes dead or damaged cells Attempts to recognize and remove abnormal cells

Pathogens: Bacteria and Viruses Table 24-1

Body Defenses: Two Lines of Defense Physical and chemical barriers Skin, epithelial linings, and cilia Acids, mucus, and lysozymes Immune defenses Innate immunity Non-specific – responds to a range of signals Immediate response Acquired immunity Specific – attacks a specific pathogen or antigen Slower but stronger response Memory allows for fast responses upon re-exposure

Leukocytes Mediate Immunity Granulocytes Eosinophils Basophils and mast cells Neutrophils Agranulocytes Monocytes and macrophages Lymphocytes

Phagocytosis of Pathogens Without Capsules Recognizing the pathogen Phagocytosis of Pathogens Without Capsules Phagocytosis of Pathogens With Capsules Figure 24-6a

Antigen-Presenting Cells Lysosome Antigen Membrane proteins Nucleus Macrophage Macrophage digests antigen in lysosome. Antigen-presenting macrophage displays antigen fragments on surface receptors. Figure 24-5

Activation of T Lymphocytes 1 Cell binds to T lymphocyte. 2 Signal transduction activates T lymphocyte. MHC-antigen complex T-cell receptor T lymphocyte MCH receptor Figure 24-15

Each Lymphocyte Clone has a Unique Surface Receptor All lymphocytes contain proteins on their cell surface capable of binding a foreign antigen Lymphocytes that all bind a particular antigen are called a clone A clone is a group of lymphocytes that are specific to one antigen. Clone 1 Clone 2 Clone 3 Figure 24-9

Four Steps in an Immune Response Detection and identification of the foreign substance Communication with other immune cells Recruitment of other immune cells, and coordination of the response Destruction or suppression of the invader Get in groups and use these general steps to draw a diagram describing ALL the steps we discussed in class. They are a total of 10 steps!!

Innate Immunity: Internal Non-specific Defenses Phagocytes ingest foreign cells and chemicals Macrophages Neutrophils Natural killer (NK) cells kill tumor cells and infected cells Cytokines mediate the inflammatory response Inflammation Fever

NK Cells Kill Infected and Tumor Cells NK cells induce apoptosis in infected cells NK cells attack some tumor cells NK cell secrete chemical signals called interferons Interferon-alpha and interferon-beta Prevent viral replication Interferon-gamma Activates macrophages and other immune cells

Inflammation Infection or tissue damage stimulates a set of local nonspecific reactions called inflammation Three beneficial roles of inflammation are to: Attract immune cells and chemical mediators to sites of infection Create physical barriers to prevent infections from spreading Promote tissue repair

Steps in the Inflammatory Response Chemical signals called cytokines are released upon tissue damage or infection Acute-phase proteins help prevent tissue damage Cytokines stimulate histamine release from mast cells Histamine causes two local vascular changes: vasodilation  leads to heat and redness nearby capillaries become more permeable 2a - wbc’s and plasma proteins move into tissue 2b - edema (swelling) results from the osmotic effect of the plasma proteins

Immune Response Chemicals - Functional Classes Table 24-2

Antibody Structure Figure 24-12

Antibodies Antibodies are also known as gamma globulins Five classes of antibodies vary in their Fc region IgG - most common, secondary response is IgG IgA - secretory form (saliva, tears, breast milk, etc.) IgE - involved in allergic responses IgM - antibodies involved in primary response IgD - found on surface of B cells, role unclear

Functions of Antibodies Figure 24-13

Major Histocompatibility Complex Major histocompatibility complex (MHC) proteins help our immune system defend against intracellular pathogens and cancers MHC class I proteins Found on all nucleated cells of the body Recognized by cytotoxic T cells MHC class II proteins Found only on antigen-presenting cells Recognized by helper T cells

Allergic Responses An allergy is an inflammatory response to a nonpathogenic antigen (called an allergen) Immediate hypersensitivity reaction Occur within minutes Mediated by antibodies Delayed hypersensitivity reaction Occur after several days Mediated by helper T cells and macrophages

Blood Types: ABO Blood Groups No A or B antigens Blood type Antigen on red blood cell Antibodies in plasma “Anti-A” and “anti-B’” “Anti-B” “Anti-A” None to A or B A antigens B antigens A and B antigens O A B AB (a) (b) Mixture of Type A and O Figure 24-20a

Immune System Pathologies - Can you explain them with your current knowledge? Allergies Autoimmune Immuno-deficiency

Stress Alters Immune System Function Nonspecific stimuli (“stressors”) disrupt homeostasis Two types of stress elicit two types of response Acute stress results in the fight-or-flight reaction Chronic stress elevates cortisol levels, which suppresses immune responses Figure 24-21