Ch 18 Immune System

Antibody Structure

• No information provided

Actions of Antibodies

• Direct attack: agglutination, precipitation, neutralization, and activation of complement
• Agglutination: antigens clump together
• Precipitation: antigens become insoluble
• Neutralization: antigens lose toxic properties
• Activation of complement: opsonization, chemotaxis, inflammation, and lysis

Mechanism of Antibody Action

• No information provided

Cell-Mediated Immunity (CMI)

• T-cells mature in the thymus gland and become activated T-cells when an antigen is detected
• Activated T-cells bind to antigen using specific receptors
• Activated T-cells differentiate into:
  • Killer T-cells (directly attack antigen)
  • Helper T-cells (release lymphokines and cytokines to facilitate plasma cells and enhance killer T-cells)
  • Memory T-cells (retain specific antigen receptors for future attack)
  • Suppressor T-cells (inhibit plasma cells, killer T-cells, and helper T-cells when antigen is destroyed)

Major Types of T Cells

• No information provided

T Cell Activity

• Antigen-bearing agents enter tissues
• Accessory cells (macrophages) phagocytize antigen-bearing agents and digest them in lysosomes
• Nonspecific (innate) resistance: a general defense mechanism against foreign substances, quickly activated but short-term and unable to recognize or remember antigens

First Line of Body Defense

• Consists of skin and mucous membrane
• Includes mechanical and chemical factors, such as keratin protein and stratified squamous epithelium in skin, and sebum and sweat in dermis

Second Line of Body Defense

• Consists of antimicrobial substances that degenerate or break up antigens
• Includes interferons, lysozymes, and complement proteins

Complement Activation

• No information provided

Third Line of Body Defense

• Consists of inflammation and phagocytosis
• Inflammation: an autonomic response by body tissues when attacked by an antigen, producing 4 major symptoms:
  • Redness (due to vasodilatation)
  • Swelling (due to increased capillary permeability)
  • Heat (due to hyperemia)
  • Pain (not mentioned)

Functions of the Lymphatic System

• Lymphatic capillaries reabsorb excessive tissue fluid and transport it through the lymphatic pathway
• Lymphatic capillaries absorb certain fatty acids in the small intestine
• Lymphatic system consists of tissues and organs that produce, mature, and store lymphocytes and macrophages for body defense
• Lymph flows from lymphatic vessels into lymphatic trunks, and finally into collecting ducts, which dispose it into the subclavian veins

Anatomy of the Immune System

• No information provided

Lymphatic Vessels

• Structurally identical to veins, with 3 thin layers of tissue and valves to prevent backflow
• Form specialized lymphatic organs called lymph nodes, which store macrophages and lymphocytes to eliminate foreign substances in the lymph
• Collecting ducts: formed by the convergence of larger lymphatic vessels, draining lymph fluid back to the blood

Lymph Nodes

• Specialized lymphatic organs attached to lymphatic vessels, producing and storing large numbers of lymphocytes and macrophages for body defense
• Found mainly in the neck, armpits, and abdominal cavity (attached to the mesentery membrane of the intestines)

Antibody Structure

• Antibodies are globular proteins called immunoglobulin (Ig)
• There are five classes of immunoglobulin: IgG, IgA, IgM, IgD, and IgE

Actions of Antibodies

• Direct attack on antigens
• Agglutination: antigens clump together
• Precipitation: antigens become insoluble
• Neutralization: antigens lose toxic properties
• Activation of complement: a set of enzymes that attack antigens
• Opsonization: alters cell membranes, making them susceptible to phagocytosis
• Chemotaxis: attracts macrophages and neutrophils to the region
• Inflammation: promotes local tissue changes to prevent the spread of antigens
• Lysis: cell membranes rupture

Cell-Mediated Immunity (CMI)

• T-cells mature in the thymus gland and become activated when an antigen is detected
• Antigen-presenting cells (APCs) find the antigen and bring it to the activated T-cells
• Activated T-cells bind to the antigen using specific receptors
• Activated T-cells differentiate into:
  • Killer T-cells: directly attack the antigen
  • Helper T-cells: release lymphokines to facilitate plasma cells in AMI and release cytokines to enhance killer T-cells
  • Memory T-cells: retain specific antigen receptors for future attack of the same antigen
  • Suppressor T-cells: inhibit plasma cells, killer T-cells, and helper T-cells when the antigen is destroyed

T Cell Activity

• Antigen-bearing agents enter tissues
• Accessory cells, such as macrophages, phagocytize the antigen-bearing agent and digest it
• Activated T-cells bind to the antigen using specific receptors and differentiate into various types

B-Lymphocytes

• Antibody production:
  • Activated B-cells proliferate and differentiate into plasma cells and memory B-cells
  • Plasma cells synthesize and secrete antibodies
  • Antibodies combine with antigen-bearing agents, helping to destroy them

Phagocytosis

• Adhesion: macrophages bind to the antigen
• Ingestion: macrophages engulf the antigen using endocytosis
• Digestion: lysosomes in macrophages release lysozymes and break down the antigen
• Excretion: macrophages discard the degenerated antigen using exocytosis

Specific (Adaptive) Resistance

• Highly specific body defense mechanisms that can recognize, destroy, and remember the antigen
• Lymphocytes recognize foreign substances as antigens because they recognize all cells in the body as "self" before birth
• Antigens are usually proteins or polysaccharides on the outer walls of microorganisms

Antibody-Mediated Immunity (AMI)

• Activated B-cells look for the antigen and bind to it using their receptors
• Helper T-cells release cytokines when they encounter a B cell that has previously combined with an identical antigen-bearing agent
• Cytokines stimulate the B cells to proliferate and differentiate into plasma cells, which secrete antibodies

Cytokines

• Cytokines are polypeptides synthesized and secreted by T-cells to enhance certain cellular responses to antigens
• Types of cytokines:
  • Colony-stimulating factors: stimulate bone marrow to produce lymphocytes
  • Interferons: block viral replication, stimulate macrophages to engulf viruses, stimulate B cells to produce antibodies, and attack cancer cells
  • Interleukins: control lymphocyte differentiation and growth
  • Tumor necrosis factor: stops tumor growth, releases growth factors, causes fever, and stimulates lymphocyte differentiation