Ch. 22 Part 3

Immunity Overview

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

• Resistance: Body's ability to maintain immunity.

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

Types of Immunity

• Innate Immunity:

  • Nonspecific defense mechanism against any type of invading agent.

• Adaptive Immunity:

  • Specific immunity that protects against particular antigens.

Lymphocytes

• Types of Lymphocytes:

  • B Cells: Part of adaptive immunity; mature in bone marrow.

  • T Cells: Part of adaptive immunity; mature in thymus.

  • NK Cells (Natural Killer): Part of innate immunity.

• Distribution: B and T cells have different distributions in tissues; can travel through blood vessels or lymphatic system.

• Longevity: Lymphocytes can survive for many years (up to 20 years).

Lymphocytopoiesis (Lymphocyte Production)

• Location: Involves bone marrow, thymus, and peripheral lymphoid tissues.

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

  • Group 1: Produce B cells and NK cells (B cells mature with interleukin-7).

  • Group 2: Produce T cells (mature with hormonal exposure).

Role of NK Cells

• Remain in red bone marrow, producing NK cells and B cells.

• Conduct immune surveillance by attacking foreign cells, virus-infected body cells, and cancer cells.

• Mechanism: Secrete chemicals to lyse plasma membranes of abnormal cells.

Antibody-Mediated Immunity

• B Cells: When stimulated, differentiate into plasma cells, which secrete antibodies.

• Function of Antibodies: Attach to pathogens, initiating a chain reaction leading to pathogen destruction.

Innate Defenses

• Characteristics: Born with these defenses; nonspecific.

• First Line of Defense: Include physical barriers, phagocytes, immune surveillance, interferons, complement system, inflammation, fever.

Physical Barriers in Innate Immunity

• Components:

  • Outer skin layer, hair, epithelial layers of internal passageways.

  • Secretions that flush away materials and kill/inhibit microorganisms.

Phagocytes

• Function: Attack and remove dangerous microorganisms.

• Types:

  • Microphages: Includes neutrophils and eosinophils; exit bloodstream to fight infections.

  • Macrophages: Large phagocytic cells making up the monocyte-macrophage system.

Activated Macrophages

• Responses:

  • Engulf and destroy pathogens using lysosomal enzymes.

  • Bind pathogens for destruction by other cells.

  • Release toxic chemicals into interstitial fluid to destroy pathogens.

Types of Macrophages

• Fixed Macrophages (Histiocytes): Stay in specific tissues (e.g., microglia in the CNS, Kupffer cells in the liver).

• Free Macrophages: Wander the body (e.g., alveolar macrophages in lungs).

Immune Surveillance

• ** NK Cells**: Act as "police" in circulation; detect cells marked as abnormal.

• Mechanism: Release perforins to target and destroy abnormal cells.

Interferons (IFNs)

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

• Role: Cytokines that initiate local immune responses.

Complement System

• Definition: Composed of plasma proteins assisting antibodies in destroying pathogens.

• Activation Pathways:

  • Classical pathway, lectin pathway, alternative pathway.

• Outcome: Inflammation and opsonization aid in pathogen destruction.

Effects of Inflammation

• Purpose: Temporarily repair and prevent more pathogens from entering the wound; slows pathogen spread; mobilizes defenses.

• Signs and Symptoms: Redness, heat, swelling, pain.

• Products of Inflammation: Necrosis, pus, abscess.

Fever

• Definition: Body temperature exceeding 37.2ºC (99ºF).

• Effects: Increases metabolic rate, accelerates defenses, inhibits certain viruses/bacteria.

Pyrogens

• Definition: Fever-inducing agents that prompt the hypothalamus to raise body temperature.

• Sources: Produced by bacteria, molds, viruses, and yeasts; includes endogenous pyrogens such as interleukin-1 and interferons.