Ch21 Total (Immune System)

What are the two intrinsic defense systems?

Innate (nonspecific) system and adaptive (specific) defense system.

What is the first line of defense?

Skin and mucosae prevent entry of microorganisms.

What is the second line of defense?

Antimicrobial proteins, phagocytes, and other cells inhibit spread of invaders throughout the body.

What is the most important mechanism of the innate defense system?

Inflammation.

What is the third line of defense?

The adaptive defense system mounts an attack against particular foreign substances.

What makes up the first line of defense?

Skin, mucous membranes, and their secretions.

What does keratin in the skin do?

Presents a physical barrier to most microorganisms and is resistant to weak acids and bases, bacterial enzymes, and toxins.

How do mucosae protect the body?

Mucosae provide similar mechanical barriers.

How does skin acidity protect the body?

Skin acidity (pH of 3 to 5) inhibits bacterial growth.

What does sebum do?

Sebum contains chemicals toxic to bacteria.

How does the stomach protect the body?

Stomach mucosae secrete concentrated HCl and protein-digesting enzymes.

What do saliva and lacrimal fluid contain?

Lysozyme.

What does mucus do?

Mucus traps microorganisms that enter the digestive and respiratory systems.

How do the respiratory tract mucosae protect the body?

Mucus-coated hairs in the nose trap inhaled particles, and cilia sweep dust- and bacteria-laden mucus away from lower respiratory passages.

What are the internal defenses?

Phagocytes and natural killer (NK) cells, antimicrobial proteins in blood and tissue fluid, and the inflammatory response.

What are the chief phagocytic cells?

Macrophages.

What do free macrophages do?

Wander throughout a region in search of cellular debris.

What are Kupffer cells?

Fixed macrophages found in the liver.

What are microglia?

Fixed macrophages found in the brain.

What do neutrophils do?

Become phagocytic when encountering infectious material.

What do eosinophils do?

Are weakly phagocytic against parasitic worms.

What do mast cells do?

Bind and ingest a wide range of bacteria.

What are natural killer (NK) cells?

Cells that kill cancer cells and virus-infected body cells.

What is the inflammatory response?

A response that enlists macrophages, mast cells, WBCs, and chemicals.

What are the four main signs of inflammation?

Redness, heat, swelling, and pain.

What causes redness and heat during inflammation?

Increased blood flow to the injured area.

What causes swelling during inflammation?

Increased capillary permeability allows fluid to enter the tissues.

What causes pain during inflammation?

Inflammatory chemicals and swelling stimulate nerve endings.

What are the four main phases of phagocytic mobilization?

Leukocytosis, margination, diapedesis, and chemotaxis.

What is leukocytosis?

Neutrophils are released from the bone marrow in response to leukocytosis-inducing factors released by injured cells.

What is margination?

Neutrophils cling to the walls of capillaries in the injured area.

What is diapedesis?

Neutrophils squeeze through capillary walls and begin phagocytosis.

What is chemotaxis?

Inflammatory chemicals attract neutrophils to the injury site.

What do antimicrobial proteins do?

Attack microorganisms directly and hinder microorganisms' ability to reproduce.

What are the most important antimicrobial proteins?

Interferon and complement proteins.

What is interferon (IFN)?

Proteins that help protect neighboring cells against viral reproduction.

What happens when a host cell is invaded by a virus?

Genes that synthesize IFN are activated.

What does interferon do?

Interferon molecules leave the infected cell and enter neighboring cells.

What does PKR do?

PKR nonspecifically blocks viral reproduction in the neighboring cell.

What do interferons also activate?

Macrophages and mobilize NKs.

What do lymphocytes secrete?

Gamma (γ) interferon.

What do most other WBCs secrete?

Alpha (α) interferon.

What do fibroblasts secrete?

Beta (β) interferon.

What is complement?

About 20 proteins that circulate in the blood in an inactive form.

What does complement do?

Provides a major mechanism for destroying foreign substances in the body.

What are the functions of complement?

Amplifies all aspects of the inflammatory response, kills bacteria and certain other cell types, and enhances the effectiveness of both nonspecific and specific defenses.

What are the two complement pathways?

Classical and alternative.

What activates the classical pathway?

Binding of antibodies to invading organisms and subsequent binding of C1 to the antigen-antibody complexes.

What activates the alternative pathway?

Interaction among factors B, D, and P, and polysaccharide molecules present on microorganisms.

What does C3b do?

Initiates formation of a membrane attack complex (MAC) and causes opsonization.

What does the membrane attack complex (MAC) do?

Causes cell lysis.

What does C3a do?

Causes inflammation.

What is C-reactive protein (CRP)?

A protein produced by the liver in response to inflammatory molecules.

What is CRP used to assess?

The presence of an acute infection and an inflammatory condition and its response to treatment.

What does C-reactive protein do?

Binds to PC receptor of pathogens and exposed self-antigens, targets damaged cells for disposal, and activates complement.

What is a fever?

Abnormally high body temperature in response to invading microorganisms.

What are pyrogens?

Chemicals secreted by leukocytes and macrophages exposed to bacteria and other foreign substances.

Why can moderate fever be beneficial?

The liver and spleen sequester iron and zinc, and the metabolic rate increases, which speeds up tissue repair.

Why are high fevers dangerous?

They can denature enzymes.

What is the adaptive immune system?

A functional system that recognizes specific foreign substances and acts to immobilize, neutralize, or destroy foreign substances.

What are the characteristics of adaptive immunity?

Antigen-specific, systemic, and has memory.

What are the two arms of adaptive immunity?

Humoral, or antibody-mediated immunity, and cellular, or cell-mediated immunity.

What are antigens?

Substances that can mobilize the immune system and provoke an immune response.

What are the ultimate targets of immune responses?

Mostly large, complex molecules not normally found in the body (nonself).

What is immunogenicity?

Ability to stimulate proliferation of specific lymphocytes and antibody production.

What is reactivity?

Ability to react with products of activated lymphocytes and the antibodies released in response to them.

What are complete antigens?

Foreign protein, nucleic acid, some lipids, and large polysaccharides.

What are haptens?

Small molecules that are not immunogenic but are reactive when attached to protein carriers.

What can happen when haptens link up with the body's proteins?

The adaptive immune system may recognize them as foreign and mount a harmful attack (allergy).

Where are haptens found?

Poison ivy, dander, some detergents, and cosmetics.

What are antigenic determinants?

Certain parts of an entire antigen that are immunogenic.

What do antibodies and activated lymphocytes bind to?

Antigenic determinants.

What do most naturally occurring antigens have?

Numerous antigenic determinants that mobilize several different lymphocyte populations and form different kinds of antibodies against it.

What are self-antigens?

Protein molecules on our cells that are not antigenic to us but are strongly antigenic to others.

What are MHC proteins?

Proteins that mark a cell as self.

Where are Class I MHC proteins found?

On virtually all body cells.

Where are Class II MHC proteins found?

On certain cells in the immune response.

What are MHC proteins coded for by?

Genes of the major histocompatibility complex (MHC).

What does each MHC molecule have?

A deep groove that displays a peptide.

What do MHC proteins do in infected cells?

Bind to fragments of foreign antigens, which play a crucial role in mobilizing the immune system.

Where do lymphocytes originate?

From hematopoietic stem cells in the bone marrow.

Where do B cells mature?

In the bone marrow.

Where do T cells mature?

In the thymus.

What is immunocompetence?

The ability of a lymphocyte to recognize and bind to a specific antigen.

What is positive selection?

The process that ensures T cells can recognize self-MHC molecules.

What is negative selection?

The process that eliminates lymphocytes that react strongly to self-antigens.

What are antigen-presenting cells (APCs)?

Cells that process antigens and present antigen fragments to T cells.

What are examples of antigen-presenting cells?

Macrophages, dendritic cells, and B cells.

What do APCs display?

Antigen fragments bound to Class II MHC proteins.

What is clonal selection?

An antigen binds to a specific lymphocyte, causing it to proliferate and form a clone of cells.

What happens during clonal selection?

An antigen binds to a receptor on a specific B lymphocyte, causing proliferation to form a clone.

What are plasma cells?

Cells that secrete antibodies.

How many antibody molecules can a plasma cell secrete per second?

About 2,000 molecules per second.

What do secreted antibodies do?

Bind to free antigens and mark the antigens for destruction by specific or nonspecific mechanisms.

What are memory B cells?

Cells that can mount an immediate response to subsequent exposures of the same antigen.

What is the primary immune response?

Cellular differentiation and proliferation, which occurs on the first exposure to a specific antigen.

How long is the lag period during the primary immune response?

3 to 6 days after antigen challenge.

When are peak antibody levels achieved during the primary response?

About 10 days.

What happens to antibody levels after the primary response peaks?

Antibody levels then decline.

What is the secondary immune response?

Re-exposure to the same antigen.