The immune system: flashcards, quiz and summary

Flashcards

1. 1Why is innate immunity described as fast and general, while adaptive immunity is slower but specific?

   Innate immunity uses barriers and general cells and chemicals that respond to many kinds of pathogens right away. Adaptive immunity relies on B and T cells that each have receptors for one antigen shape, so it takes time to activate and multiply the right cells, but it targets a particular pathogen very precisely.

2. 2What is an antigen, and why does each B or T cell respond to only one kind?

   An antigen is a molecule, usually a protein or polysaccharide, that triggers an immune response. Each B or T cell has receptors for only one antigen shape, so only the lymphocyte that matches a given antigen is activated.

3. 3What happens to a lymphocyte when it meets its matching antigen?

   It is activated and divides into many identical copies. This is clonal selection, and it is how the body builds up enough cells to fight a specific pathogen.

4. 4How do B cells and plasma cells produce the antibody response?

   Activated B cells become plasma cells that release large numbers of antibodies, and some B cells become memory B cells. Antibodies neutralize viruses and toxins, clump pathogens together, and tag them for phagocytes, mainly targeting pathogens in blood and body fluids.

5. 5What is the role of helper T cells in the cell-mediated response?

   Helper T cells are activated when an antigen-presenting cell, such as a macrophage, shows them an antigen piece. They release cytokines that switch on B cells and cytotoxic T cells. Because HIV infects helper T cells, both responses are weakened.

6. 6How do cytotoxic T cells deal with virus-infected cells?

   They recognize body cells that display foreign antigens and kill them directly. This is different from antibodies, which act on pathogens in body fluids.

7. 7What makes the secondary immune response faster and stronger than the primary response?

   Memory cells from the first exposure are already present, so they react within days. Antibody levels rise faster, reach higher levels and last longer, which is why you often never feel sick the second time.

8. 8How does a vaccine protect a person without causing the disease?

   A vaccine presents an antigen, such as killed or weakened pathogens, pathogen pieces, inactivated toxins, or mRNA coding for one pathogen protein. The body mounts a primary response and forms memory cells, so a real infection meets a fast secondary response.

9. 9What is the difference between active and passive immunity?

   Active immunity means your own body makes antibodies and memory cells, either from infection or a vaccine, and it lasts a long time. Passive immunity means you receive ready-made antibodies, such as from a mother or an antivenom injection, which works immediately but fades in weeks to months because no memory cells are made.

Practice quiz

Pick an answer to check it.

1. 1Which statement best describes the difference between innate and adaptive immunity?

   1. Innate immunity is slow and specific, while adaptive immunity is fast and general.
   2. Innate immunity builds memory cells, while adaptive immunity only uses physical barriers.
   3. Innate immunity is fast and general, while adaptive immunity is slower at first but specific and builds memory.
   4. Both are equally fast, but only adaptive immunity uses white blood cells.
   Show the answer

   C. Innate immunity is fast and general, while adaptive immunity is slower at first but specific and builds memory. Innate immunity responds quickly and generally, using barriers and cells like neutrophils. Adaptive immunity is slower at first, targets specific antigens, and forms memory cells.

2. 2A patient's B cells have just been activated by an antigen. Which cell type will release antibodies into the blood?

   1. Cytotoxic T cells
   2. Plasma cells
   3. Natural killer cells
   4. Helper T cells
   Show the answer

   B. Plasma cells Activated B cells become plasma cells, which pour out antibodies. Cytotoxic T cells kill infected cells directly, helper T cells release cytokines, and natural killer cells are part of innate immunity.

3. 3Why does a person often not feel sick on a second exposure to the same pathogen?

   1. Phagocytes permanently disappear after the primary response.
   2. Antigens are destroyed by stomach acid during the first infection.
   3. The body stops making antibodies after the first infection.
   4. The secondary response is faster and larger because memory cells already exist.
   Show the answer

   D. The secondary response is faster and larger because memory cells already exist. Memory cells from the primary response react within days. Antibody levels rise faster, go higher and last longer, which often prevents illness.

4. 4A doctor gives a patient antivenom after a snake bite. What type of immunity does this provide, and what is its main limitation?

   1. Passive immunity, which works right away but fades in weeks to months
   2. Active immunity, which lasts for life
   3. Active immunity, which only works after 1 to 2 weeks
   4. Passive immunity, which creates lasting memory cells
   Show the answer

   A. Passive immunity, which works right away but fades in weeks to months Antivenom is ready-made antibody given by injection, so it is artificial passive immunity. It works immediately but fades because no memory cells are formed.

5. 5Which best explains why HIV weakens the immune system?

   1. HIV blocks phagocytes from engulfing bacteria in the blood.
   2. HIV makes cytotoxic T cells attack healthy body cells.
   3. HIV infects helper T cells, which weakens both the antibody and cell-mediated responses.
   4. HIV destroys B cells in bone marrow before they can mature.
   Show the answer

   C. HIV infects helper T cells, which weakens both the antibody and cell-mediated responses. Helper T cells release cytokines that switch on B cells and cytotoxic T cells, so losing them weakens both responses.

6. 6Which situation is an example of an autoimmune disease?

   1. The immune system attacking the nerve coatings in multiple sclerosis
   2. Sneezing and itchy eyes after breathing in pollen
   3. Swelling and redness after a cut becomes infected
   4. A severe whole-body reaction to a bee sting
   Show the answer

   A. The immune system attacking the nerve coatings in multiple sclerosis Autoimmune disease means the immune system attacks the body's own cells, as in multiple sclerosis. Pollen allergy and anaphylaxis are overreactions to harmless antigens, and swelling from a cut is inflammation.

Test traps

What teachers like to test on this, and the mistakes students make.

• Confusing antigen and antibody: the antigen is the target molecule, and the antibody is the protein that binds to it.
• Mixing up which cell does what: plasma cells (from B cells) make antibodies, while cytotoxic T cells kill infected cells directly, and students often swap these in short answers.
• Saying antibiotics fight viruses. Antibiotics work against bacteria, not viruses, and they are medicines rather than part of the immune system.
• Forgetting why passive immunity fades: it makes no memory cells, so the protection disappears over weeks to months, unlike active immunity.
• Describing the primary response as immediate. Antibody levels take about 1 to 2 weeks to peak, which is why you may get sick the first time.

Summary

• The immune system defends against pathogens such as bacteria, viruses, fungi and parasites, using innate immunity (fast and general) and adaptive immunity (slower at first, but specific and with memory).
• Innate defenses include physical and chemical barriers like skin, mucus, stomach acid and lysozyme, plus internal responses such as phagocytosis, natural killer cells, inflammation and fever.
• Antigens are molecules that trigger a response, and each B or T cell has receptors for only one antigen shape. When a matching lymphocyte meets its antigen, clonal selection makes many identical copies of it.
• The antibody response is carried out by B cells becoming plasma cells that release Y-shaped antibodies, which neutralize pathogens and tag them for phagocytes.
• The cell-mediated response uses helper T cells to switch on other immune cells and cytotoxic T cells to kill body cells displaying foreign antigens, and HIV weakens it by infecting helper T cells.
• The primary response to a first exposure is slow, while the secondary response is faster, bigger and longer-lasting because memory cells are already present.
• Vaccines trigger a primary response without causing disease, creating memory cells, and herd immunity protects people who cannot be vaccinated.
• Active immunity comes from your own body making antibodies and memory cells and lasts a long time, while passive immunity is received ready-made and fades within weeks to months.

Key terms

Pathogen

A microbe that can cause disease, such as a bacterium, virus, fungus or parasite.

Antigen

A molecule, usually a protein or polysaccharide, that triggers an immune response.

Antibody

A Y-shaped protein with two binding sites for one specific antigen, which neutralizes pathogens and tags them for phagocytes.

Phagocyte

A cell that engulfs and digests invaders through phagocytosis, such as neutrophils and macrophages.

Lymphocyte

A white blood cell made in bone marrow that includes B cells and T cells, the core cells of adaptive immunity.

Clonal selection

The process in which a lymphocyte that meets its matching antigen is activated and divides into many identical copies.

Plasma cell

An activated B cell that pours out antibodies.

Cytotoxic T cell

A T cell that kills body cells displaying foreign antigens, such as virus-infected cells.

Memory cell

A long-lived B or T cell formed after an exposure that allows a faster response on later exposure to the same antigen.

Active immunity

Immunity in which your own body makes antibodies and memory cells, either after infection (natural) or a vaccine (artificial).

Passive immunity

Immunity from ready-made antibodies received from another source, such as across the placenta, in breast milk, or by injection; it works immediately but fades.

Autoimmune disease

A condition in which the immune system attacks the body's own cells, such as the insulin-making cells in type 1 diabetes.

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