ch22 Pt 3

Immunity Overview

• Immunity: Ability to resist and defend against infectious organisms and damaging substances.

• Resistance: The body's capacity to maintain immunity.

• Immune Response: The body's reaction to infectious agents and other abnormal substances.

Types of Immunity

• Innate (Nonspecific) Immunity:

  • Defends against any type of invading agent.

• Adaptive (Specific) Immunity:

  • Protects against specific antigens.

Lymphocytes in Immune System

• Each immunity system utilizes lymphocytes:

  • B Cells: Specific immunity.

  • T Cells: Specific immunity.

  • NK Cells: Innate immunity.

• Travel and Survival:

  • Lymphocytes circulate through blood vessels or lymphatic system.

  • Maintain the ability to divide essential for immune function.

  • Can survive for many years (up to 20).

Lymphocytopoiesis

• Definition: Production of lymphocytes.

• Key Structures:

  • Bone Marrow: Site of lymphocyte production.

  • Thymus: Maturation site for T cells.

  • Peripheral Lymphoid Tissues: Site for lymphocyte differentiation.

• Stem Cells: Hemocytoblasts in bone marrow divide into two types of lymphoid stem cells.

Lymphoid Stem Cells Differentiation

• Group 1:

  • Produces B cells and NK cells.

  • B Cells: Differentiate with interleukin-7 (IL-7).

• Group 2:

  • Produces T cells.

  • Differentiation: Occurs with hormonal exposure.

NK Cells Function

• Production: Derived from lymphoid stem cells in red bone marrow.

• Role:

  • Attack foreign cells, infected body cells, and cancer cells.

  • Secrete chemicals to lyse plasma membranes of abnormal cells.

B Cells Function

• When stimulated, B cells differentiate into plasma cells.

• Plasma Cells: Produce and secrete antibodies that attach to pathogens, initiating a destruction chain reaction.

Innate Defenses

• Definition: Defenses individuals are born with; nonspecific against antigens.

• First Line of Defense includes:

  • Physical barriers:

    • Outer skin layer

    • Hair

    • Epithelial layers of passageways

    • Secretions that flush materials and inhibit microorganisms.

Phagocytes

• Attack and remove dangerous microorganisms.

• Two Classes of Phagocytes:

  • Microphages:

    • Neutrophils and eosinophils.

    • Exit circulation to enter tissues for infection fights.

  • Macrophages:

    • Large phagocytic cells throughout the body.

    • Form monocyte-macrophage system (reticuloendothelial system).

Activated Macrophages Functions

• Respond to pathogens by:

  • Engulfing and destroying pathogens using lysosomal enzymes.

  • Binding to pathogens for other cells to destroy.

  • Releasing toxic chemicals into interstitial fluid to destroy pathogens.

Types of Macrophages

• Fixed Macrophages (Histiocytes): Stay in specific tissues (e.g. dermis).

• Free Macrophages (Wandering Macrophages): Travel throughout the body (e.g. alveolar macrophages in lungs).

Immune Surveillance

• Conducted by NK cells acting as 'police' in circulation.

• Detect abnormal cells through surface antigens and release perforins.

Tumor-Specific Antigens

• Found on cancer cell membranes, recognized as abnormal by NK cells.

• Cells infected with viruses display abnormal proteins, which allows NK cells to identify and destroy them.

Interferons (IFNs)

• Definition: Small proteins released by activated lymphocytes, macrophages, and virally infected cells.

• Role of Cytokines: Chemical messengers that initiate local responses; Interferons are a type of cytokine.

Complement System

• Composed of proteins in plasma that assist antibodies in pathogen destruction.

• Activation Routes:

  • Classical pathway

  • Lectin pathway

  • Alternative pathway (all lead to inflammation and opsonization).

Inflammation

• Effects:

  • Temporary repair of tissue.

  • Prevention of additional pathogens entering wounds.

  • Slowing the spread of pathogens.

  • Mobilization of defense mechanisms.

• Cardinal Signs:

  • Redness

  • Heat

  • Swelling

  • Pain

• Products of Inflammation:

  • Necrosis

  • Pus

  • Abscess.

Fever

• Defined as a body temperature over 37.2ºC (99ºF).

• Effects:

  • Increases metabolic rate

  • Accelerates immune defenses

  • Inhibits some viruses and bacteria.

• Pyrogens: Fever-inducing agents that cause hypothalamus to raise body temperature, produced by bacteria and viruses (e.g. interleukin-1, interferons, tumor necrosis factor).