Innate Immunity Chapter 15

First Line of Defense Structures, chemicals, processes that work to prevent pathogens entering the body…Barriers to Entry Nonspecific defenses Includes the skin and mucous membranes of the respiratory, digestive, urinary, and reproductive systems Animation: Host Defenses PLAY

Skin – Physical Components of Defense Epidermis Outer layer composed of multiple layers of tightly packed cells Few pathogens can penetrate these layers Shedding of dead skin cells removes attached microorganisms Epidermal dendritic cells (Langerhans cells) These are able to phagocytize pathogens Dermis Contains protein fibers …collagen Give skin strength and pliability to resist abrasions that could introduce microorganisms

Skin – Chemical Components of Defense Perspiration secreted by sweat glands Salt – inhibits growth of pathogen by drawing water from their cells Antimicrobial peptides – sweat glands secret dermicidins Lysozyme – destroys cell wall of bacteria Sebum secreted by sebaceous (oil) glands Helps keep skin pliable and less likely to break or tear Lowers the pH of the skin to a level inhibitory to many bacteria

Mucous Membranes Line all body cavities open to the outside environment Epithelium Thin, outer covering of the mucous membranes Unlike surface epidermal cells, epithelial cells are living Tightly packed to prevent entry of pathogens Continual shedding of cells carries attached microorganisms away

Microbial Antagonism Normal microbiota help protect the body by competing with potential pathogens Various activities of the normal microbiota make it hard for pathogens to compete Consumption of nutrients makes them unavailable to pathogens Create an environment unfavorable to other microorganisms by changing pH

Other First-Line Defenses Many body organs secrete chemicals with antimicrobial properties Example: lacrimal glands that bathe the eye

More First Line Defenses

Second Line of Defense Operates when pathogens succeed in penetrating the skin or mucous membranes Nonspecific defense Composed of cells, antimicrobial chemicals, and processes but no physical barriers Many of these components are contained or originate in the blood

Blood Composed of cells and portions of cells within a fluid called plasma Plasma is mostly water containing electrolytes, dissolved gases, nutrients, and proteins When the clotting factors (a group of plasma proteins) are removed from plasma, the remaining fluid is called serum Other plasma proteins include complement proteins and antibodies The cells and cell fragments in plasma are called formed elements

Formed Elements Three types of formed elements Erythrocytes – carry oxygen and carbon dioxide in the blood Platelets – involved in blood clotting Leukocytes – involved in defending the body against invaders Two groups Granulocytes Agranulocytes

Granulocytes Contain large granules that stain different colors based on the dye used Basophils – stain blue with the basic dye methylene blue Eosinophils – stain red/orange with the acidic dye eosin Neutrophils – stain lilac with a mixture of acidic and basic dyes Neutrophils and eosinophils can phagocytize pathogens White blood cells are capable of diapedesis

Agranulocytes Cytoplasm appears uniform under a light microscope Two types lymphocytes – most involved in adaptive immunity monocytes – leave the blood and mature into macrophages

Phagocytic cells of the second line of defense Macrophages Phagocytic cells of the second line of defense Wandering macrophages leave the blood via diapedesis and phagocytize throughout the body Fixed macrophages do not move throughout the body and often phagocytize within a specific organ Include alveolar macrophages (lungs), microglia (central nervous system), Küpffer cells (liver) All macrophages, plus monocytes attached to endothelial cells, constitute the mononuclear phagocytic system

Lab Analysis of Leukocytes The differential white blood cell count (the diff) can signal signs of disease Increased eosinophils can indicate allergies or parasitic worm infection Bacterial diseases often show increase in leukocytes and in neutrophils Viral infections may show increase in lymphocytes

Components of the Second Line of Defense Phagocytosis Extracellular killing by leukocytes Nonspecific chemical defenses Inflammation Fever

Phagocytosis Cells capable of phagocytosis are called phagocytes Animation: Phagocytosis PLAY

Extracellular Killing by Leukocytes Three Cell types that kill extracellularly Eosinophils Mainly attack parasitic helminths (worms) by attaching to their surface Secrete toxins that weaken or kill the helminth Natural killer lymphocytes (NK cells) Secrete toxins onto the surface of virally infected cells and tumors Neutrophils Produce chemicals that kill nearby invaders

Nonspecific Chemical Defenses Some chemicals augment phagocytosis Some attack pathogens directly Some enhance other features of innate immunity Nonspecific chemical defenses includes Lysozyme Complement Interferon Defensins

Complement System Set of serum proteins designated numerically according to the order of their discovery Complement activation results in lysis of the foreign cell Complement can be activated in several ways Classical pathway Complement named for the events of this originally discovered pathway…the various complement proteins act nonspecifically to “complement” the action of antibodies Alternate pathway Activation occurs independent of antibodies

Complement – Two Pathways Figure 15.10

Inactivation of Complement Body’s own cells withstand complement cascade Membrane-bound proteins on many cells bind with and break down activated complement proteins Animation: The Complement System PLAY

Interferons Protein molecules released by host cells to nonspecifically inhibit the spread of viral infections

Inflammation Nonspecific response to tissue damage resulting from various causes Characterized by redness, heat, swelling, and pain Two types Acute Chronic Animation: Inflammation PLAY

Acute vs. Chronic Inflammation Acute inflammation Develops quickly and is short lived Is usually beneficial Important in the second line of defense Dilation and increased permeability of the blood vessels Migration of phagocytes Tissue repair Chronic inflammation Develops slowly and lasts a long time Can cause damage to tissues

Increased Vascular Permeability during Inflammation

Events in Inflammation Figure 15.17.1

Events in Inflammation Figure 15.17.2

Fever A body temperature over 37C Results when chemicals called pyrogens trigger the hypothalamus to increase the body’s core temperature Various types of pyrogens Bacterial toxins Cytoplasmic contents of bacteria released by lysis Antibody-antigen complexes These signal for the production of interleukin-I (IL-1)

Fever Production IL-1 production causes the hypothalamus to secrete prostaglandin which resets the hypothalamic “thermostat” Communication with the brain initiates muscle contractions, increased metabolic activity, and constriction of blood vessels which raises the body’s temperature Chills associated with fever are due to the reduced blood flow of constricted vessels Decrease in IL-1 production results in the body’s temperature returning to normal

Benefits of Fever Enhances the effects of interferons Inhibits growth of some microorganisms May enhance the performance of phagocytes, cells of specific immunity, and the process of tissue repair

A Summary of Some Nonspecific Components of the First and Second Lines of Defense Table 15.5