The Immune System Practice Questions

25 multiple-choice questions on The immune system for paramedic and EMT students, from Chapter 26 (Immunologic Emergencies). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

25 practice questions

1. The main function of the immune system is to:

   1. A. Return tissue fluid to the blood
   2. B. Break down toxins in the liver
   3. C. Produce the clotting factors
   4. D. Defend the body against invaders
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   Answer: D. Defend the body against invaders

   The immune system recognizes and destroys bacteria, viruses, toxins, and abnormal cells while sparing the body's own tissues. Returning tissue fluid to the blood is a job of the lymphatic vessels. Breaking down toxins is a liver function, and the liver also makes the clotting factors.

2. A patient with large partial-thickness burns is at high risk of infection mainly because:

   1. A. The skin barrier has been lost
   2. B. Heat inactivates circulating antibodies
   3. C. Burned skin releases too much IgE
   4. D. Burns stop bone marrow cell production
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   Answer: A. The skin barrier has been lost

   Intact skin is the body's first, innate barrier against microbes. Burns remove it, so bacteria can invade the wound directly, which is why burn care stresses clean dressings. Burns do not inactivate circulating antibodies or halt marrow production in the first hours, and IgE drives allergy rather than infection defense.

3. A child has strep throat twice in one year. Adaptive immunity from the first episode did not prevent the second most likely because:

   1. A. Antibiotics erase the body's immune memory
   2. B. Immune memory fades within days
   3. C. The new strain has different antigens
   4. D. Strep bacteria carry no antigens
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   Answer: C. The new strain has different antigens

   Adaptive immunity is specific: antibodies and memory cells recognize the exact surface antigens they were made against. Group A strep has many strains with different surface proteins, so immunity to one may not protect against another. Antibiotics do not erase memory, memory lasts far longer than days, and all bacteria carry antigens.

4. Before a kidney transplant, the donor and recipient are tested for matching tissue (HLA) antigens mainly to:

   1. A. Prevent allergy to the surgery drugs
   2. B. Lower the risk of graft rejection
   3. C. Confirm the donor's blood glucose
   4. D. Avoid passing on hepatitis B
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   Answer: B. Lower the risk of graft rejection

   HLA molecules are antigens on nearly all cells that the immune system uses to tell self from non-self. The closer the match, the less likely the recipient's T cells are to attack the graft. Infection screening and blood tests are done separately, and HLA typing has nothing to do with drug allergy.

5. Antibodies help neutrophils kill bacteria mainly by:

   1. A. Turning bacterial toxins into toxoids
   2. B. Coating them for easier engulfment
   3. C. Raising the body's core temperature
   4. D. Releasing histamine onto the bacteria
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   Answer: B. Coating them for easier engulfment

   Coating a microbe with antibody (or complement) is called opsonization. Phagocytes have receptors for the antibody's tail, so coated bacteria are engulfed far more easily. Antibodies do not make toxoids (toxoids are vaccine products) or set body temperature, and histamine comes from mast cells.

6. A woman with a cat allergy starts sneezing and wheezing within minutes of entering a friend's home. The reaction is so fast because:

   1. A. IgE is already bound to her mast cells
   2. B. Her T cells must first be activated by it
   3. C. Cat dander is a direct airway toxin
   4. D. She is making new IgM against the cat
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   Answer: A. IgE is already bound to her mast cells

   Sensitized people already carry allergen-specific IgE on their mast cells. When the allergen bridges those IgE molecules, the cells release histamine and other mediators within minutes. T-cell (type IV) reactions take a day or more, new antibody production takes days, and dander is harmless to people who are not sensitized.

7. A lab report shows IgM antibody against hepatitis A but no IgG. This pattern suggests:

   1. A. Immunity from a past vaccine
   2. B. Lifelong protection from an old infection
   3. C. A recent or current infection
   4. D. Antibodies passed from the mother
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   Answer: C. A recent or current infection

   IgM is the first antibody made in a new infection; IgG follows later and persists. IgM without IgG therefore points to a recent infection. Vaccine-derived and long-standing immunity show IgG, and the antibodies that cross the placenta are IgG.

8. A healthy 7-month-old is catching more colds than she did as a newborn. A normal reason is that:

   1. A. Her thymus has stopped making T cells
   2. B. Breast milk now blocks her antibodies
   3. C. Her vaccines have weakened her defenses
   4. D. Antibodies from her mother have faded
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   Answer: D. Antibodies from her mother have faded

   Maternal IgG crosses the placenta and protects the infant for the first few months, then breaks down. Until the infant builds her own antibodies, minor infections become more common around 6 months. The infant thymus is very active, breast milk adds protective IgA, and vaccines strengthen rather than weaken immunity.

9. Long-term use of an acid-reducing drug such as omeprazole raises the risk of some gut infections because:

   1. A. The drug destroys white blood cells
   2. B. The drug blocks antibody production
   3. C. Acid normally kills swallowed germs
   4. D. Low acid makes the bowel empty faster
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   Answer: C. Acid normally kills swallowed germs

   Gastric acid is a chemical part of innate immunity. With less acid, more swallowed bacteria survive into the intestine, which is linked to higher rates of C. difficile and other enteric infections. Proton pump inhibitors do not destroy white cells or block antibody production.

10. Anti-rejection drugs such as tacrolimus protect a transplanted kidney mainly by suppressing:

    1. A. T cells that would attack the graft
    2. B. Mast cells that release histamine
    3. C. Platelets that clot the graft vessels
    4. D. Red cell production in the marrow
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    Answer: A. T cells that would attack the graft

    Rejection is driven mainly by the recipient's T cells recognizing the donor organ as foreign. Calcineurin inhibitors such as tacrolimus block T-cell activation. The trade-off is a higher risk of infection, which is why these patients need careful infection control.

11. A splinter left in a finger for 3 days now has a pocket of pus. Pus consists mainly of:

    1. A. Leaked plasma from damaged vessels
    2. B. Lymph fluid from a blocked node
    3. C. Clotted blood and trapped platelets
    4. D. Dead neutrophils and bacteria
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    Answer: D. Dead neutrophils and bacteria

    Neutrophils rush to the site, engulf bacteria, and die. The thick fluid that collects is pus: dead white cells, bacteria, and tissue debris. Clear fluid leaked from vessels is serous fluid, and clotted blood is a hematoma, not pus.

12. Helper T cells (CD4 cells) are the main target of:

    1. A. Hepatitis B
    2. B. HIV
    3. C. Influenza
    4. D. Tuberculosis
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    Answer: B. HIV

    As HIV destroys CD4 cells, the patient becomes vulnerable to opportunistic infections.

13. A man with spring pollen allergy gets an itchy, tingling mouth each time he eats a raw apple, with no other symptoms. This is most likely:

    1. A. Oral allergy (pollen-food) syndrome
    2. B. Early hereditary angioedema
    3. C. Contact dermatitis of the lips
    4. D. An anaphylactoid reaction to the fruit
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    Answer: A. Oral allergy (pollen-food) syndrome

    Proteins in some raw fruits resemble tree-pollen proteins, so pollen-sensitized patients react in the mouth. Symptoms are usually mild and limited to the lips and mouth because the proteins break down in the stomach, and cooking destroys them. Hereditary angioedema does not itch, and contact dermatitis is delayed. Throat tightness or systemic signs would still call for anaphylaxis care.

14. A child has eczema, seasonal hay fever, and asthma. These conditions share:

    1. A. An infection with the same virus
    2. B. A lack of working T cells
    3. C. Damage caused by autoimmune antibodies
    4. D. A tendency to make IgE to allergens
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    Answer: D. A tendency to make IgE to allergens

    Atopy is an inherited tendency to become IgE-sensitized to ordinary environmental allergens. Eczema, allergic rhinitis, asthma, and food allergy often occur together. They are not caused by a shared infection, a T-cell deficiency, or autoimmunity.

15. Mast cells are found mainly in:

    1. A. The circulating blood only, as cells
    2. B. The bone marrow only
    3. C. Connective tissue near vessels
    4. D. The red blood cell membrane
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    Answer: C. Connective tissue near vessels

    Mast cells line the skin, airways, and GI tract, which is why these areas react first in anaphylaxis.

16. Two days after a cat scratch on the hand, a patient has a red streak running up the forearm and a tender lump in the armpit. This shows that:

    1. A. A clot has formed in a superficial vein
    2. B. Infection is tracking along lymphatics
    3. C. The patient is allergic to the cat's saliva
    4. D. Normal healing is under way at the wound
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    Answer: B. Infection is tracking along lymphatics

    A red streak toward the trunk (lymphangitis) with a tender axillary node means bacteria are moving through the lymphatic vessels to the regional lymph node, which swells as it fights them. This needs prompt antibiotics because it can progress to bacteremia. Allergy and normal healing do not cause a tracking streak and a tender node.

17. Leukotrienes released in anaphylaxis mainly cause:

    1. A. Prolonged bronchoconstriction
    2. B. Rapid, sustained bronchodilation
    3. C. Increased cardiac output
    4. D. Lower capillary leak and edema
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    Answer: A. Prolonged bronchoconstriction

    Leukotrienes act more slowly than histamine but cause stronger, longer-lasting bronchospasm.

18. The hepatitis B vaccine contains only one viral surface protein, not the whole virus. It can still protect because:

    1. A. It kills the virus on contact
    2. B. It supplies ready-made antibodies
    3. C. It blocks the liver's virus receptors
    4. D. The protein acts as an antigen
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    Answer: D. The protein acts as an antigen

    The immune system needs only the antigen, not the live virus, to make antibodies and memory cells. A single surface protein (HBsAg) is enough, and it cannot cause infection. The vaccine does not kill virus directly, contains no antibodies (that would be passive immunity, such as HBIG), and does not block liver receptors.

19. Before RSV season, a newborn receives nirsevimab, an injected ready-made antibody against RSV. This gives the infant:

    1. A. Active immunity that lasts for many years
    2. B. A mild RSV infection to build memory
    3. C. Passive immunity for about one season
    4. D. Memory B and T cells against RSV
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    Answer: C. Passive immunity for about one season

    Nirsevimab is a long-acting monoclonal antibody. Because the infant receives antibody rather than making it, protection is passive: it starts right away and wanes over about 5 months, roughly one RSV season. It does not cause infection or create memory cells.

20. A paramedic gets her flu vaccine the day before a large influenza outbreak at a nursing home she covers. She should assume that she is:

    1. A. Fully protected starting the next morning
    2. B. Not yet protected for about 2 weeks
    3. C. Contagious with flu from the vaccine
    4. D. Protected after 12 hours of rest
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    Answer: B. Not yet protected for about 2 weeks

    After vaccination the body needs about 2 weeks to make protective antibodies, so she should keep using PPE and hand hygiene in the meantime. Injected flu vaccines are inactivated and cannot give her influenza.

21. After a bone marrow (stem cell) transplant, patients usually repeat their childhood vaccines because:

    1. A. Their spleen was removed for transplant
    2. B. Old vaccines cause graft-versus-host disease
    3. C. Donor antibodies make them allergic
    4. D. Their old immune memory is lost
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    Answer: D. Their old immune memory is lost

    The conditioning chemotherapy wipes out the recipient's own immune cells, including memory cells from earlier vaccines and infections. The new marrow has to be taught again, so vaccines are repeated on a schedule after transplant. The spleen is not removed, and vaccines do not cause graft-versus-host disease.

22. A 30-year-old takes eculizumab, a drug that blocks complement, and now has a fever of 39.4 °C (103 °F) and chills that began 3 hours ago. The main concern is:

    1. A. Fast-moving meningococcal infection
    2. B. A mild viral cold that will pass
    3. C. A delayed allergic reaction to the drug
    4. D. A flare of the disease being treated
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    Answer: A. Fast-moving meningococcal infection

    Complement is needed to kill Neisseria bacteria. Blocking it raises the risk of meningococcal disease more than 1,000-fold, and the infection can progress to septic shock within hours, even in vaccinated patients. Fever in these patients is an emergency. A cold, drug reaction, or flare is possible but is not the threat to rule out first.

23. A 60-year-old has a red, hot, swollen knee, a fever of 38.9 °C (102 °F), and cannot bear weight. The most dangerous cause to consider is:

    1. A. A simple strain of the knee ligaments
    2. B. An osteoarthritis flare-up
    3. C. Septic (infected) arthritis
    4. D. A ruptured Baker's cyst
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    Answer: C. Septic (infected) arthritis

    Inflammation causes redness, heat, swelling, and pain, but fever with a hot joint and inability to bear weight suggests bacteria in the joint. Septic arthritis can destroy cartilage within days and can lead to sepsis, so it needs prompt hospital care. Strains and osteoarthritis do not cause fever.

24. In Graves disease, the thyroid becomes overactive because the patient's autoantibodies:

    1. A. Destroy cells of the pituitary gland
    2. B. Switch on the thyroid like TSH
    3. C. Block iodine from entering
    4. D. Attack and destroy the thyroid
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    Answer: B. Switch on the thyroid like TSH

    In Graves disease, autoantibodies bind the TSH receptor and stimulate the gland continuously, causing hyperthyroidism. Antibodies that destroy the thyroid cause the opposite, Hashimoto hypothyroidism. Autoimmunity can either damage or overstimulate its target.

25. Hypersensitivity is best defined as:

    1. A. A complete lack of immunity
    2. B. A normal response to infection
    3. C. A temporary loss of sensation
    4. D. An exaggerated immune response
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    Answer: D. An exaggerated immune response

    Allergic reactions are one form of hypersensitivity.