Ch. 20: The Immune System

What is the function of the immune system?

To defend the body against disease-causing microorganisms, cancer cells, and foreign tissues, such as transplanted organs or skin grafts.

What are the two major divisions of the immune system?

Innate defenses and Adaptive defenses.

Innate defenses are nonspecific, present from birth, have no memory, and no antibodies.

True

What are the two types of innate defenses?

Surface barriers and internal defenses.

What are examples of surface barrier defenses?

Skin and mucous membranes.

What role do surface barriers play in immunity?

They act as the first line of defense to keep invaders out of the body.

What are the three types of surface barriers?

Mechanical (skin and mucous membranes), Chemical (secretions), and Microbial (good bacteria).

Which is external and which is internal: skin vs mucous membranes?

Skin is external; mucous membranes are internal.

What are the three secretions mucous membranes produce for defense?

Acid pH (skin, vagina, stomach), enzymes like lysozyme (tears, stomach), and mucin.

What is mucin?

Sticky mucus in mucous membranes that traps bacteria in respiratory, digestive, and reproductive tracts.

What are internal innate defenses?

Cells and chemicals that act as the second line of defense if the first line is penetrated.

What are the five main internal innate defenses?

Phagocytes, Natural Killer (NK) cells, inflammation, antimicrobial proteins, and fever.

What are phagocytes and how do they work?

White blood cells (neutrophils and monocytes) that engulf cells with unusual membrane markers recognized as foreign.

What are Natural Killer (NK) cells and what do they target?

Aggressive lymphocytes in blood and lymph that lyse cancerous cells and virus-infected cells.

How do Natural Killer cells kill abnormal cells?

By inducing apoptosis, not by phagocytosis.

What triggers inflammation?

Tissue injury from infection, trauma, or intense heat.

What are the main outcomes and hallmarks of inflammation?

Stops the spread of agents, cleans debris, prepares tissue repair; hallmarks: heat, redness, swelling, pain.

What are the three stages of the inflammation response?

Arteriole dilation, increased capillary permeability, and chemotaxis of WBCs.

What happens during arteriole dilation?

Arterioles dilate, blood flow increases, heat and redness appear, and extra nutrients are delivered for repair.

What occurs when capillary permeability increases?

Protein-rich fluid (exudate) leaks into tissues, clotting trapped pathogens, causing pain, swelling, and possibly reduced mobility.

What is chemotaxis in inflammation?

Attraction of WBCs to the injury site to attack pathogens, clean debris, release inflammatory chemicals, and form pus.

What is the purpose of all inflammation responses?

Healing

What are antimicrobial proteins?

Non-specific proteins with no memory, including interferons and complement proteins (MAC).

What is the role of interferon?

Produced by virus-infected cells to signal neighboring cells to produce antiviral proteins, slowing viral spread.

Which illness may be treated with pre-made interferon?

Hepatitis C.

What is the complement system and MAC?

A group of plasma proteins that bind abnormal membranes, marking them for destruction; MAC = Membrane Attack Complex.

What is the role of fever in immunity?

Pyrogens from WBCs raise body temperature, aiding healing.

Are adaptive defenses the first, second, or third line of defense?

Third line of defense.

What are three characteristics of adaptive defense?

Specificity, systemic response, and memory.

What is humoral immunity?

Immunity in which B lymphocytes produce antibodies that circulate in the blood and lymph to target specific invaders.

What is cell-mediated immunity?

Immunity in which cytotoxic T cells directly attack infected or abnormal cells.

What is an antigen?

A chemical, usually a non-self protein, that provokes an immune response.

What are self-antigens and the major histocompatibility complex (MHC)?

Self-proteins on cell surfaces; MHC proteins help immune cells distinguish self from non-self.

Who would have identical MHC proteins?

Only identical twins.

What is an antibody?

Gamma globulin protein that binds a specific antigen; types include IgA, IgM, IgG.

What are the three main cells of the adaptive immune system?

B-lymphocytes, T-lymphocytes, and antigen-presenting cells.

Where do B and T lymphocytes originate?

Red bone marrow.

Where do B and T lymphocytes mature?

B cells in bone marrow; T cells in thymus.

When B lymphocytes encounter a foreign antigen, what two groups do they form?

Plasma cells and B memory cells.

What is the function of plasma cells?

They produce specific antibodies that attach to invaders, triggering lysis or marking for phagocytosis and inflammation.

What is the function of B memory cells?

Store memory of the invading antigen for a faster response in future exposures.

What are the two main types of T lymphocytes?

Helper T cells (CD4) and cytotoxic T cells (CD8).

What responses do helper T cells produce when exposed to foreign proteins?

They stimulate B cells to make antibodies, activate cytotoxic T cells, and help form memory T cells.

How do helper T cells assist B cells in humoral immunity?

They bind to B cells presenting antigen on MHC II and release interleukins to complete activation.

How do helper T cells assist cytotoxic T cells in cellular immunity?

They interact with dendritic cells, promote co-stimulatory molecule expression, and secrete interleukin-2 to activate CD8 T cells.

What are the three steps of T cell selection?

Positive selection, negative selection, clonal selection.

What occurs in T cell positive selection?

T cells that can recognize self-MHC molecules survive, while those that cannot undergo apoptosis.

What occurs in T cell negative selection?

T cells that recognize self-antigens undergo apoptosis, while those that do not recognize self-antigens survive.

What is clonal selection?

Antigens that bind to specific receptors, causing lymphocytes to clone themselves.

How do cytotoxic T cells respond to infected or abnormal cells?

They recognize and bind to target cells, release chemicals to lyse them, help reject foreign tissue (like transplants), and form memory T cells.

How does HIV affect the immune system?

It replicates in helper T cells, destroying them and impairing B and cytotoxic T cell responses.

What is AIDS?

A disease caused by HIV, leading to severe immune deficiency and vulnerability to infections and cancers.

What are the two types of acquired immunity?

Active and passive immunity.

What is active immunity?

Immunity acquired naturally through infection or artificially through vaccination, in which the body produces its own antibodies.

What is passive immunity?

Immunity acquired naturally through maternal antibodies or artificially via immune serum injections, giving immediate but short-term protection.

Why do vaccines work?

They trigger a primary response, create memory cells, and enable a faster, stronger secondary response.

What is a titer?

A measure of antibody concentration in plasma, expressed as the highest dilution showing a positive reaction.

What does a higher titer indicate?

More antibodies in plasma, as a positive reaction occurs even when highly diluted.

What are four homeostatic imbalances of the immune system?

Immunodeficiencies, immunosuppression, autoimmune disease, hypersensitivities.

What is the difference between acquired and congenital immunodeficiencies?

Acquired occurs later in life (e.g., HIV); congenital is present at birth due to nonfunctional WBCs or antibodies.

What is immunosuppression?

A decrease in immune response, caused by drugs or disease; can be intentional during therapy.

What medications induce immunosuppressive therapy?

Corticosteroids (suppress inflammation) and anti-proliferative drugs (inhibit WBC cloning).

What is an autoimmune disease?

The immune system attacks the body’s own cells, failing to recognize self-proteins.

What are examples of autoimmune diseases?

Multiple sclerosis, Graves’ disease, rheumatoid arthritis, systemic lupus erythematosus, type I diabetes, glomerulonephritis.

What are hypersensitivities?

Immune responses to harmless substances that can range from mild to life-threatening.

What are allergies and their treatments?

Mild reactions from localized histamine release; treated with antihistamines or corticosteroid creams.

What is anaphylaxis and its treatment?

Severe reaction with bronchial constriction and low blood pressure; treated with epinephrine (EpiPen) and bronchodilators.

What could happen if B cells did not require T cell help for activation?

B cells could become over-reactive and attack the body’s own cells.