Topic 3: Immunology

List the body’s three lines of defense and give one example of each…

• Physical & chemical barriers: skin, mucus, stomach acid.

• Innate immunity: Inflammation, fever, or white blood cells like macrophages.

• Adaptive Immunity: B cells producing antibodies against a specific virus.

Define which lines of defense are innate…

• 1st line: Physical & chemical barriers - skin, mucus, stomach acid

• 2nd line: Innate immunity - inflammation, fever, phagocytes

Define which lines of defense is adaptive…

• 3rd line of defense: Adaptive Immunity - B and T cells

Compare innate and adaptive immunity by speed, specificity, and memory…

• Innate - Rapid, non-specific, and no memory of pathogen.

• Adaptive - Slow, specific, has memory of pathogen.

Identify skin and mucous membranes as the first line of defense…

• Skin: Acts as a physical barrier that blocks germs from entering.

• Mucous membranes: Line areas such as the nose, mouth, respiratory tract, and digestive tract.

Explain how skin keeps pathogens out of the body…

By acting as a tough physical barrier that prevents most microorganisms from entering the body.

Explain how mucous membranes keep pathogens out of the body…

By trapping them in mucus before they can enter deeper tissues

• Nose: Mucus traps dust and microorganisms

• Respiratory: Cilia move mucus and trapped pathogens toward the throat

• Eyes: Tears wash away microorganisms

Give examples of chemical and mechanical barrier defenses…

Chemical:

• Acid mantle (Slightly acidic skin surface makes it difficult for many pathogens to grow)

• Lysozyme (Found in tears, saliva, and mucus that can break down bacterial cell walls")

• Stomach acid (Very low pH kills many pathogens swallowed with food)

Mechanical:

• Mucus (Traps pathogens so they can be removed)

• Cilia (Move mucus and trapped pathogens out of respiratory)

How do innate and adaptive immunity work together?

Innate defenses detect pathogens and help activate the adaptive immune response, which then produces a specific defense using B and T cells.

How does innate defenses help activate the adaptive immune response?

The innate immune cells detect the pathogen, release chemical signals and present antigens to T cells.

Explain how normal microbiota (normal flora) contribute to defense…

Normal flora compete with pathogens for space and nutrients and can produce substances that inhibit their growth.

Explain why a break in a barrier (wound or burn) raises infection risk…

It damages the first line of defense and creates an opening that allows pathogens to enter the body.

What are phagocytes?

Immune cells that engulf and destroy pathogens and other foreing material.

What are neutrophils?

Fast-acting white blood cells that are often among the first immune cells to arrive at an infection.

What are macrophages?

Larger cells that engulf pathogens, dead cells, and debris. They also help activate adaptive immunity.

What are the main phagocytes, and what is phagocytosis?

Neutrophils and macrophages.

Phagocytosis is the process of engulfing and digesting pathogens or cellular debris.

Explain the role of natural killer (NK) cells in destroying infected or abnormal cells…

NK cells recognize the infected or abnormal cells, and release chemicals that cause the target cell to die.

Describe the antimicrobial proteins interferon and compliment…

• Interferons help protect cells from viruses and slow viral reproduction.

• Complement is a group of blood proteins that help destroy pathogens, promote inflammation, and enhance phagocytosis.

What are the four general steps of phagocytosis and what do they do?

• Chemotaxis → “Find it”; are attracted to the chemicals released from the infection.

• Adherence → “Stick to it”; attaches to the pathogen.

• Ingestion → “Eat it”; Phagocyte engulfs the pathogen.

• Digestion → “Destroy it”; Enzymes destroy the pathogen.

How do interfreons protect neighboring cells from viral infection?

Infected cells release interferons, which warn nearby cells and trigger antiviral defenses that inhibit slow down or prevent reproduction.

How does the complement system enhance defense?

Through cell lysis (destroys pathogens), opsonization (makes pathogens easier to phagocytose), and inflammation (attracts immune cells).

Explain the role of fever as a body-wide innate defense…

A fever raises body temperature to slow pathogen growth or help kill them.

List the four cardinal signs of inflammation…

• Redness

• Heat

• Swelling

• Pain

What triggers inflammation?

Tissue injury or pathogens.

What does histamine do?

Causes vasodilation (wider blood vessels → increased blood flow), and increased permeability (leakier vessels → fluid enters tissues)

How does inflammation help the body?

Inflammation recruits phagocytes to destroy pathogens, helps contain the injury, and prepares the tissue for repair.

Put these in order:

• Phagocyte recruitment

• Repair

• Injury

• Vasodilation and leaky capillaries

• Mediators released

• Injury

• Mediators released

• Vasodilation and leaky capillaries

• Phagocyte recruitment

• Repair

Define antigen…

A substance that the immune system recognizes as foreign, triggering an immune response.

What is the difference between self and non-self antigens?

Self antigens are markers from your own cells and are normally tolerated. Non-self antigens are foreign markers that trigger an immune response.

How does an activated B cell give rise to plasma cells and memory cells?

An activated B cell divides into plasma cells, which produce antibodies, and memory B cells, which remain in the body for a faster response to future exposure.

What is capillary permeability?

How easily substances can pass through the walls of a capillary between the blood and surrounding tissues.

Explain how the swelling (edema) of inflammation relates to fluid movement out of capillaries…

• During inflammation, capillaries become more permeable, allowing more fluid and proteins to move from the blood into the surrounding tissue.

Distinguish a local inflammatory response from systemic signs such as fever and elevated white-cell count…

• The key difference is where the response occurs and how widespread it is.

• Local inflammatory response: Occurs at the site of injury or infection; Typical signs include redness, heat, swelling, pain, or loss of function.

• Systemic inflammatory response: Occurs throughout the body; Typical signs include fever and elevated white-cell count (leukocytosis).

Explain self-tolerance…

Means the immune system normally recognizes the body’s own cells and molecules as “self” and does not attack them.

Explain, at a big-picture level, how MHC "self" markers display antigens to the immune system…

MHC molecules display protein fragments (antigens) on cell surfaces for T cells to inspect, helping the immune system to distinguish normal cells from infected cells.

Connect a breakdown of self-tolerance to autoimmune disease…

When self-tolerance fails, the immune system may mistakenly attack the body’s own cells or tissues, causing autoimmune disease.

What is autoimmune disease?

A condition in which the immune system mistakenly attacks the body’s own healthy cells or tissues.

What do plasma cells do?

These secrete antibodies.

What is an anitbody?

A tiny protein that specifically binds to an antigen.

How do anitbodies defend the body?

Antibodies bind to a specific antigen, then neutralize harmful substances and tag pathogens for destruction.

Describe the Y-shaped structure of an antibody and connect its shape to its function…

The tips of the Y have two specific antigen-binding sites that attach to antigens, while the stem interacts with other parts of the immune system to help eliminate the target.

What are the four main mechanisms of antibody action?

Neutralization → blocks pathogen/toxin activity
Agglutination → clumps pathogens together
Complement activation → activates proteins that help destroy pathogens
Opsonization → tags pathogens for easier phagocytosis

What is clonal selection?

An antigen selects and activates a specific lymphocyte, which then rapidly divides into many identical clones that help eliminate the pathogen and provide immune memory.

What is the role of helper T cells?

Helper T cells coordinate the immune response by releasing signals that activate B cells, cytotoxic T cells, and other immune cells.

What is the role of cytotoxic T cells?

Cytotoxic T cells recognize and destroy infected or abnormal body cells, primarily by triggering apoptosis in the target cell.

How does cell-mediated immunity differ from humoral immunity?

Cell-mediated immunity uses T cells to target infected or abnormal cells, while humoral immunity uses B cells and antibodies to target free pathogens and antigens in body fluids.

Why are helper T cells central to the immune response, and what happens when they are lost?

Helper T cells coordinate and activate B cells, cytotoxic T cells, and other immune cells. Loss of helper T cells severely weakens the immune response, increasing susceptibility to infections.

How do cytotoxic T cells differ from NK cells in killing target cells?

Cytotoxic T cells specifically recognize antigen on MHC I, while NK cells detect general signs of abnormal or stressed cells. Both can kill target cells by triggering apoptosis.

What is the role of memory T cells?

Memory T cells remain after an initial immune response and allow a faster, stronger T-cell response if the same antigen is encountered again.

What happens during the primary immune response?

On first exposure to an antigen, there is a lag period while specific lymphocytes become activated. Antibody levels then gradually rise as plasma cells produce antibodies, and memory cells are formed.

What happens during the secondary immune response?

On re-exposure to the same antigen, memory cells respond faster and more strongly, producing a rapid, higher antibody response.

What is immunological memory, and what is the role of memory cells?

Immunological memory is the ability to remember a previously encountered antigen. Memory B and T cells remain after the initial response and allow a faster, stronger immune response upon re-exposure.

What is active immuntiy?

Active immunity occurs when your own immune system responds to an antigen and produces antibodies and memory cells.

What is passive immunity?

Passive immunity occurs when a person receives pre-made antibodies from another source, providing immediate but generally temporary protection

Give an example of active immunitiy…

An infection or vaccine

Give an example of passive immunity…

• Maternal antibodies or an antibody injection

• Newborn baby receiving antibodies from its mother through the placenta or breast milk

How does a vaccine produce active immunity?

A vaccine exposes the body to a harmless form or piece of a pathogen's antigen, activating the immune system to produce antibodies and memory cells that provide protection during future exposure.

Why does active immunity last longer than passive immunity?

Active immunity creates memory cells, allowing long-term protection. Passive immunity provides pre-made antibodies but does not create immune memory, so protection is temporary.

What are the four types of acquired immunity?

• Natural active: infection → make your own antibodies/memory cells

• Artificial active: vaccine → make your own antibodies/memory cells

• Natural passive: maternal antibodies → receive antibodies naturally

• Artificial passive: antibody treatment → receive pre-made antibodies by medical intervention

Memory trick:

Active = you make it.

Passive = you receive it.

Natural = happens naturally.

Artificial = Medical intervention.

What is herd immunity?

When enough people in a population are immune to a disease, the pathogen spreads less easily, which can provide indirect protection to people who are not immune.

What is an allergy/hypersensitivity?

An overreaction of the immune system to a normally harmless antigen (allergen), causing inflammation and other symptoms.

What is autoimmune disease and give an example…

A disease in which the immune system attacks the body's own tissues. Example: Type 1 diabetes, where immune cells attack pancreatic beta cells.

Why does the secondary immune response usually prevent you from feeling sick upon re-exposure?

Memory B and T cells respond faster and more strongly, producing antibodies and attacking the pathogen before it can multiply enough to cause significant symptoms.

How does immunological memory explain how vaccines work?

Vaccines expose the immune system to a safe form or component of a pathogen, creating memory B and T cells without causing the full disease. If exposed to the real pathogen later, these memory cells trigger a faster, stronger secondary immune response, often preventing illness or making it much milder.

What is immunodeficiency? Use HIV/AIDS as an example.

Immunodeficiency is a condition in which the immune system is weakened or unable to function properly. HIV causes immunodeficiency by attacking CD4 (helper) T cells, which are important for coordinating immune responses. As CD4 cells decline, the immune system becomes less able to fight infections, potentially leading to AIDS and opportunistic infections.

What is the role of histamine in an allergic reaction, and why do antihistamines help?

Histamine is released by mast cells during an allergic reaction. It causes itching, redness, swelling, mucus production, and increased blood vessel permeability. Antihistamines block histamine receptors, reducing these symptoms.

How does HIV cause immunodeficiency by destroying helper T cells?

HIV infects and destroys CD4 (helper) T cells, which normally coordinate immune responses by activating other immune cells. As CD4 cells decrease, the immune system becomes less able to fight infections, causing immunodeficiency and potentially leading to AIDS.

What are some examples of autoimmune diseases?

Autoimmune diseases occur when the immune system attacks the body's own cells or tissues. Examples include:

• Type 1 diabetes — attacks insulin-producing pancreatic cells

• Rheumatoid arthritis — attacks joints

• Multiple sclerosis (MS) — attacks the protective covering of nerve cells

Define innate immunity…

Innate immunity is the body’s general, non-specific defense system that provides immediate protection against pathogens. It includes barriers like skin, as well as inflammation, fever, and immune cells such as phagocytes.

Define adaptive immunity…

Adaptive immunity is a specific immune response that targets particular pathogens. It involves B cells and T cells and creates immune memory for faster protection during future exposures.