Exam 2 Immune System

What is immunology?

The study of physiological defenses used by the body to protect itself from “non-self” (foreign matter).

What are the two broad categories of immune defense?

Nonspecific/innate and specific/adaptive immunity.

What is nonspecific/innate immunity?

A broad defense that works without prior exposure to a pathogen.

• What you’re born with/already have

What is specific/adaptive immunity?

A defense that develops after prior exposure and targets a particular pathogen/antigen.

What are the major components of nonspecific immunity?

External barriers, phagocytic cells, antimicrobial proteins, inflammation, and fever.

What are the major components of specific immunity?

Cellular immunity and humoral immunity.

What is the first line of defense against infection?

External barriers of the skin and body surfaces.

How does the skin provide immune protection?

It is a physical barrier; keratin resists weak acids/bases, bacterial enzymes, and endotoxins, while acidic pH inhibits bacterial growth

How do mucous membranes protect against infection?

Mucus traps microbes, while saliva and tears contain lysozyme.

How does the stomach defend against pathogens?

Stomach mucosa secretes acid and protein-digesting enzymes.

Where are leukocytes produced?

Bone marrow

What is the primary function of neutrophils?

Nonspecific phagocytosis. They are the most abundant leukocyte.

What are eosinophils involved in?

Antiparasitic defense and hypersensitivity reactions.

What is the major role of basophils?

Release histamine, contributing to inflammation.

What are monocytes?

Circulating precursors that transform into macrophages in tissues.

What are the major functions of macrophages?

Detect pathogens, perform nonspecific phagocytosis, digest pathogens, present antigens, and produce cytokines.

What are lymphocytes?

B cells and T cells involved in specific immunity.

What do natural killer (NK) cells do?

Nonspecifically bind to and kill virus-infected and cancer cells.

What are cytokines?

Protein messengers released by immune cells that function in both nonspecific and specific immunity.

What is the primary role of cytokines?

They act as a chemical communication network that regulates immune responses.

What is inflammation?

A local response to infection or injury.

What are the two major purposes of inflammation?

• Destroy/inactivate foreign invaders

• Prepare the tissue for repair

Which cells are key components of inflammation?

Neutrophils and macrophages.

What causes redness during inflammation?

Hyperemia/increased blood flow.

What causes swelling?

Increased capillary permeability.

What causes heat?

Hyperemia/increased blood flow.

What causes pain?

Chemicals released by damaged cells and pressure on nerves.

What are the major inflammatory mediators?

Histamine, kinins (bradykinin), and eicosanoids (leukotrienes).

What are the basic steps of the nonspecific inflammatory response?

• Infection/injury → chemical mediators released

• Vasodilation

• Increased protein permeability

• Chemotaxis of leukocytes

• Phagocytic destruction of bacteria

• Tissue repair

Why does vasodilation occur during inflammation?

Increased blood flow delivers proteins and WBCs to the affected area.

What is chemotaxis?

Movement of leukocytes from the blood into the interstitial fluid of the affected area.

What mediates systemic responses to infection?

Cytokines

How does fever develop?

Pyrogens secreted by macrophages reset the body's thermostat to a higher temperature.

Why can a mild-moderate fever be beneficial?

It increases tissue metabolic rate, speeds defenses/repair, and inhibits pathogen reproduction.

Why can a high fever be dangerous?

Excessive heat can cause inactivation of enzymes and may be deadly.

What happens to plasma iron and zinc during infection?

They decrease; reduced iron availability helps limit bacterial multiplication.

What is the acute-phase response in inflammation?

The liver increases production of proteins (ex: C-reactive protein) that help minimize tissue damage and enhance repair.

What happens to WBC production during infection?

Bone marrow production increases.

What metabolic changes occur during systemic infection?

Amino acids are released from muscle and fatty acids are released as an energy source.

What are interferons?

Cytokines released by cells in response to viral infection.

How do interferons help fight viral infection?

They trigger production of antiviral proteins that inhibit viral replication.

What is complement?

A family of 30+ plasma proteins activated in response to infection or tissue damage.

What are the essential cells of specific immunity?

Lymphocytes

What is an antigen?

Any molecule or cell capable of triggering an immune response against it.

What are the two major types of specific immunity?

Humoral immunity and cellular immunity.

What cells mediate humoral immunity?

B cells.

What cells mediate cellular immunity?

T cells.

What is humoral immunity?

Antibody-mediated immunity involving B cells.

What is cellular immunity?

Cell-mediated immunity involving T cells through direct attack, enhanced inflammation, or lymphocyte activation.

Where do T cells mature?

In the thymus.

Where do T cells undergo cell division?

In lymphoid organs such as the spleen, tonsils, adenoids, and lymph nodes.

What are the four major T-cell subsets?

• Cytotoxic T cells

• Helper T cells

• Regulatory/suppressor T cells

• Memory T cells

What do cytotoxic T cells (CD8+) do?

Directly attack and kill target cells using secreted chemicals.

What do helper T cells (CD4+) do?

Secrete cytokines that assist/activate B cells and cytotoxic T cells.

Why are helper T cells important in HIV?

They are essential for adequate B-cell and cytotoxic T-cell function.

What do regulatory/suppressor T cells do?

Inhibit B-cell and cytotoxic T-cell activity and help slow the immune response after the pathogen disappears.

How may regulatory T cells help prevent autoimmune disease?

By inhibiting excessive B- and T-cell activity.

What do memory T cells do?

Recognize an antigen in the future and allow a faster immune response.

What are the three basic steps of specific immune defense?

• Encounter and recognize antigen

• Activate lymphocytes

• Attack using activated lymphocytes and/or antibodies

What is the major histocompatibility complex (MHC)?

A protein complex on cell membranes that allows T-cell receptors to recognize antigen.

Why is MHC important for T-cell recognition?

T-cell receptors cannot recognize an antigen unless it is presented with the appropriate MHC protein.

Where is MHC Class I found?

On all body cells except red blood cells.

What is the role of MHC Class I?

Allows body cells to function as antigen-presenting cells for cytotoxic T cells.

What happens during cytotoxic T-cell activation?

Antigen presentation + helper T-cell cytokine stimulation → cytotoxic T-cell activation → direct attack of foreign/infected cells.

What do perforins do?

Create a leaky cell membrane in the target cell.

• Render it non-functional

What do lymphotoxins do?

Destroy the target cell's DNA.

What is the role of helper T cells in both cellular and humoral immunity?

They secrete cytokines that facilitate cytotoxic T-cell and B-cell activity, coordinating both immune responses.

Where do B cells mature?

Bone marrow.

What happens when a B cell binds its antigen?

Antigen presentation plus helper T-cell cytokines activates the B cell.

What do activated B cells become?

Plasma cells that produce antibodies.

What else is produced during B-cell activation?

Memory B cells.

What is the purpose of memory B cells?

Allow a faster, stronger response to future exposure to the same antigen.

What is the most abundant antibody class?

IgG (75–85%).

What is the role of IgM?

Provides major specific immunity against bacteria and viruses, is a potent agglutinating/clumping agent, and activates complement.

What is the primary role of IgA?

Protects mucosal surfaces of the GI, respiratory, and urinary tracts.

Where is IgA especially important?

Breast milk.

What is the primary role of IgE?

Mediates allergic/hypersensitivity responses.

How does IgE contribute to allergic responses?

Stimulates histamine release from basophils/mast cells and attracts eosinophils.

What is active immunity?

The body produces its own memory cells, antibodies, and T cells in response to an antigen.

What are the two types of active immunity?

• Natural: infection/natural exposure

• Artificial: vaccination

What is passive immunity?

Direct transfer of antibodies to an individual.

What is the major characteristic of passive immunity?

It is temporary.

What are examples of natural passive immunity?

IgG through the placenta and IgA through breast milk.

What is an example of artificial passive immunity?

Injection of immune serum, such as for snakebite or rabies.

Why does active immunity provide a stronger response during a second exposure?

Memory cells are present, producing a much larger antibody response.

What is immune tolerance?

The body's ability to avoid mounting an immune response against its own proteins.

How are self-reactive T cells eliminated during development?

T cells that recognize self-proteins are destroyed through apoptosis/clonal deletion.

Can B cells also undergo mechanisms that prevent self-reactivity?

Yes. Clonal inactivation also occurs with B cells.

What is an autoimmune disease?

An inappropriate immune attack against the body's own proteins.

Give examples of autoimmune diseases

• Myasthenia gravis → ACh receptors

• Multiple sclerosis → myelin

• Rheumatoid arthritis → joints

• Type I diabetes → insulin-producing pancreatic cells

What is hypersensitivity?

An immune response to an environmental antigen that causes inflammation and damage to the body itself.

Is the allergen itself necessarily harmful?

No. The immune response causes the damage.

What are the four types of hypersensitivity?

• Delayed

• Immune-complex

• Cytotoxic

• Immediate

What is immediate hypersensitivity?

An antibody-mediated response involving IgE, mast cells/basophils, and inflammatory mediator release.

What happens during re-exposure in immediate hypersensitivity?

A much stronger response occurs because IgE triggers mast cells to release inflammatory mediators.

What are common localized symptoms of immediate hypersensitivity?

Increased mucus, swelling, congestion, sneezing, and difficulty breathing.

What is anaphylaxis?

A systemic hypersensitivity response when inflammatory cells/mediators enter circulation

What is cytotoxic hypersensitivity?

Antibody-mediated damage or destruction of cells.

What is an example of cytotoxic hypersensitivity?

Hemolytic disease of the newborn.

What is immune-complex hypersensitivity?

Antigen-antibody complexes deposit in tissues and trigger intense inflammation.