Chapter 14 Outline
Resistance and the Immune System: Innate Immunity
Introduction
14.1 An Overview of Host Immune Defenses
 Blood Cells Form an Important Defense for Innate and Acquired Immunity
• Serum is the fluid part of blood, containing:
• minerals
• salts
• proteins, etc.
• Plasma is serum that contains clotting agents
• Leukocytes (white blood cells) are produced in the bone marrow
• Neutrophils (polymorphonuclear leukocytes [PMNs]) are
phagocytes
• Eosinophils contain toxic compounds to defend against
multicellular parasites
• Basophils are similar to mast cells, acting in allergic reactions
• Monocytes are phagocytes that mature into macrophages in tissue
• Lymphocytes move to the lymph nodes after maturation
• Natural killer (NK) cells destroy virus-infected and abnormal cells
• B lymphocytes and T lymphocytes are involved in acquired
immunity
• Dendritic cells are found in the skin and other points of pathogen origin
• They are involved in acquired immunity
 The Lymphatic System Is Composed of Cells and Tissues Essential to
Immune Function
• Lymph is the clear fluid surrounding tissue cells and filling intercellular
spaces
• The lymphatic system maintains and distributes lymphocytes
• The primary lymphoid tissues are the thymus and bone marrow
• The secondary lymphoid tissues are the spleen and lymph nodes
• The spleen contains cells that monitor and fight infectious
microbes
• The lymph nodes contain phagocytes and lymphocytes
 Innate and Acquired Immunity Are Essential Components of a Fully
Functional Human Immune System
• Innate immunity (nonspecific resistance) is genetically-encoded to
recognize:
• common pathogenic features
• foreign substances
• Cytokines are chemical signals sent by many immune cells to tissues
involved with initiating acquired immunity
• Acquired immunity (specific resistance) involves production of:
• lymphocytes
• antibodies specific to the pathogen causing infection
14.2 The Innate Immune Response
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Mechanical, Chemical, and Microbiological Barriers Are Exposed First Lines
of Defense
• The skin is a mechanical barrier
• Breaches of the skin may allow microbes to enter the blood
• If a pathogen is detected by Langerhans cells, they phagocytize it
and induce an acquired immune resonse
• Mucous membrane cells produce mucus to trap microbes
• Lactobacillus in the human vagina decrease the pH, which resists infection
• The low pH in the stomach destroys most pathogens
• Defensins are antimicrobial peptides found in various bodily secretions
• Lysozyme, found in tears, sweat, and saliva, lyses gram-positive bacterial
cells
• Interferons are cytokines that trigger:
• macrophage activation
• production of substances to interfere with RNA viral reproduction
• The normal microbiota of the body outcompete pathogens for nutrients
and attachment sites
Phagocytosis Is a Nonspecific Defense Mechanism to Clear Microbes from
Infected Tissues
• Phagocytosis is the capture and digestion of foreign particles
• Chemokines are cytokines that attract macrophages and neutrophils to
infected tissues
• Opsonins attach to microbes to increase the ability of phagocytes to adhere
(opsonization)
• Phagocytized microbes are held in a phagosome
• The phagosome is acidified, killing or inactivating the pathogen
• Phagosomes also fuse with lysosomes (phagolysosome)
• Enzymes and other products kill and digest the pathogen
Moderate Fever Benefits Host Defenses
• Low to moderate fever supports the immune system by:
• inhibiting rapid microbial growth
• encouraging rapid tissue repair
• heightening phagocytosis
• Pyrogens are cytokines produced by:
– some leukocytes
– fragments from pathogens
• They affect the hypothalamus, causing elevated body temperature
• If a temperature rises above 105°F in an adult, host metabolic inhibition
can occur
• This can cause convulsions and death
Natural Killer Cells Recognize and Kill Abnormal Cells
• NK cells are formed in the bone marrow, and migrate to:
• tonsils
• lymph nodes
• spleen
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When activated, they produce cytokines that trigger response by
macrophages and other cells
Then they move into blood and lymph where they kill:
• cancer cells
• virus-infected cells
When an NK cell recognizes a cell as “nonself” it releases cytotoxic perforins
and granzymes
Complement Marks Pathogens for Destruction
• Complement is a series of proteins that circulate in the bloodstream
• They activate in the presence of microbes
• In the classical pathway, antibody-microbe complexes activate
complement proteins that activate C3 convertase
• In the alternative pathway, the complement protein C3 binds to the
pathogen cell surface to activate C3 convertase
Innate Immunity Depends on Receptor-Recognition of Common PathogenAssociated Molecules
• Pathogen-associated molecular patterns (PAMPs) help the innate immune
system recognize pathogens
• Toll-like receptors (TLRs) are signaling receptors on:
• macrophages
• dendritic cells
• endothelial cells
TLRs mediate a specific response to distinct PAMPs
They stimulate the secretion of cytokines
• For example, those that stimulate production of acute phase proteins
The TLR response must be regulated to prevent infection and immune
disorders