Chapter 22 The Immune System Part C

Two Intrinsic Defense Systems Innate (nonspecific) system Immunity: Two Intrinsic Defense Systems Innate (nonspecific) system responds quickly Adaptive (specific) defense system Takes longer to react than the innate system

Innate (nonspecific) Defense System Innate system consists of two components: First line of defense: Includes external body barriers Second line of defense: Includes internal defenses:

Innate Nonspecific Defenses

Innate (nonspecific) Defense System: Surface Barriers Make up the first line of defense Include: Skin (keratin in the skin): Physical barrier to most microorganisms & their toxins Resists weak acids & bases Mucosae: Similar mechanical barriers Line all body cavities open to the exterior

Chemical Barriers Epithelial membranes produce protective chemicals: Skin acidity (pH of 3 to 5) inhibits bacterial growth Sebum contains chemicals toxic to bacteria Stomach mucosae secrete: Concentrated HCl Protein-digesting enzymes

Chemical Barriers, cont’d. Saliva & lacrimal fluid contain lysozyme Mucus traps microrganisms & particles entering: The digestive system The respiratory system

Internal Defenses: Cells and Chemicals Called upon when 1st line of defense is penetrated Nonspecific cellular & chemical devices: Phagocytes Natural killer (NK) cells Antimicrobial proteins (in blood and tissue fluid) Inflammatory response (other cells involved) Fever

Phagocytes Macrophages: Chief phagocytic cells Include two types: Free macrophages: Regional wanderers Searching for invaders & cellular debris Ex. alveolar macrophages Fixed macrophages: Confined to a particular organ, Ex. Kupffer cells (liver) Microglia (brain) Figure 21.2a

Phagocytes (Macrophages) Figure 21.2a

Phagocytes, cont’d Neutrophils: Eosinophils: Most abundent WBCs Become phagocytic on encountering infectious material Eosinophils: Weakly phagocytic Important in defending against parasitic worms

Mechanism of Phagocytosis Microbes adhere to the phagocyte Pseudopods form & engulf the particle (antigen) into a phagosome Phagosomes fuse with a lysosome (phagolysosome) Proteolytic enzymes of phagolysosome digest invaders Indigestible & residual material is removed by exocytosis Some organisms escape phagocytosis unrecognized

Microbe adheres to phagocyte. 1 Microbe adheres to phagocyte. 2 Phagocyte forms pseudopods that eventually engulf the particle. Phagocytic vesicle containing antigen (phagosome). Lysosome 3 Phagocytic vesicle is fused with a lysosome. Phagolysosome 4 Microbe in fused vesicle is killed and digested by lysosomal enzymes within the phagolysosome, leaving a residual body. Acid hydrolase enzymes Residual body 5 Indigestible and residual material is removed by exocytosis. (b) Figure 21.2b

Natural Killer (NK) Cells Large granular lymphocytes (Small distinct group) Police the blood & lymph Nonphagocytic and nonspecific Can lyse and eliminate cancer and virus-infected cells Kill by: Releasing perforins & other cytolytic chemicals Enhance inflammatory response by: Secreting potent chemicals

Inflammation: Tissue Response to Injury Triggered whenever body tissues are injured by: Physical trauma Intense heat Chemical irritants Infectiuos agents: Viruses Bacteria Fungi

Inflammation Response The four major signs of acute inflammation are: Redness Heat Swelling Pain Beneficial effects: Prevents local spread of damaging agents Disposes off cell debris and pathogens Sets the stage for repair processes

Inflammation Response Released chemicals cause: Dilatation of local small blood vessels Vessel dilatation leads to: Increased blood flow Hyperemia (blood congestion) Hyperemia accounts for: Redness, & Heat of inflamed area

Inflammatory Response: Vascular Permeability Chemicals liberated also cause: Increased perrmeability of local capillaries Fluid seeps thru capillaries into tissue spaces causing: Edema (local swelling) Seeped fluid contains: Clotting factors Proteins Antibodies

Inflammatory Response: Edema Contributes to the sensation of pain Helps dilute harmful substances Brings in large quantities of Oxygen, and Nutrients needed for repair Allows entry of: Clotting proteins, which prevent the spread of bacteria

Inflammatory Response: Phagocytic Mobilization Four main phases: Leukocytosis: Injured cells release leukocytosis-inducing factors Bone marrow responds by releasing neutrophils Margination: Neutrophils cling to the walls of capillaries in injured area Diapedesis: Neutrophils squeeze thru capillaries & begin phagocytosis Chemotaxis: Inflammatory chemicals attract more neutrophils to injury site

Innate defenses Internal defenses 4 Positive chemotaxis Inflammatory chemicals diffusing from the inflamed site act as chemotactic agents 1 Neutrophils enter blood from bone marrow 3 Diapedesis 2 Margination Endothelium Basement membrane Capillary wall Figure 21.4

Antimicrobial Proteins The most important antimicrobial proteins are: Interferon Complement proteins Enhance the innate defenses by: Directly attacking microorganisms Hindering microorganism reproductive ability

Virus-invaded host cell activates synthesis of IFN Interferon (IFN) Virus-invaded host cell activates synthesis of IFN Interferon molecules: Leave the infected cell Enter neighboring cells Interferon stimulates neighboring cells to: Activate genes to produce antiviral proteins Antiviral proteins: Nonspecifically block viral reproduction in neighboring cells

Interferon (IFN) Figure 21.5

Interferon Family Interferon Family: They include: A number of related proteins With slightly different physiological effects They include: Gamma () interferon: secreted by lymphocytes Alpha () interferon: secreted by most other WBCs Beta () interferon: secreted by fibroblasts

Interferon Family, cont’d. In addition to the antiviral effect, interferons also: Activate macrophages Mobilize NKs FDA-approved alpha IFN is used: As an antiviral drug against hepatitis C virus To treat genital warts caused by the herpes virus

At least 20 proteins that circulate in the blood Complement At least 20 proteins that circulate in the blood Present in an inactive form in blood Provides a major mechanism for destroying foreign substances in the body Enhances the effectiveness of both: Nonspecific defenses Specific defenses

Fever Abnormally high body temperature Occurs in response to invading microorganisms Body temperature is regulated by: A cluster of neurons in the hypothalamus Referred to as the body’s thermostat The thermostat is reset upwards in response to pyrogens Pyrogens are chemicals secreted: By leukocytes and macrophages In response to exposure to bacteria & other foreign substances

High fever is dangerous because it: Fever (cont’d.) High fever is dangerous because it: Denatures enzymes Shuts down metabolism Moderate fever can be beneficial, as it: Stimulates the liver & spleen to sequester iron and zinc (needed by microorganisms) Increases metabolic rate speeding up tissue repair