1. A child who has no thymus gland suffers from frequent infections. Why?
The thymus is where T lymphocytes (T cells) mature. Without a functional thymus, the body cannot produce enough mature T cells, making it difficult to recognize and destroy infected cells and pathogens.
2. Why do swollen lymph nodes usually indicate that the body is fighting an infection?
Lymph nodes filter lymph and trap pathogens. During an infection, white blood cells multiply rapidly inside the lymph nodes, causing them to enlarge and become tender.
3. Why are newborn babies protected against some diseases even before receiving vaccines?
Babies receive antibodies from their mother through the placenta before birth and through breast milk after birth. This provides temporary passive immunity.
4. A vaccinated person becomes infected with the same pathogen years later. Why is the illness usually much milder?
Vaccination creates memory B cells and memory T cells. These cells recognize the pathogen immediately and produce a much faster immune response, preventing severe disease.
5. Why are people who have had their spleen removed at greater risk of infection?
The spleen filters pathogens from the blood and contains many immune cells. Without it, bacteria and damaged blood cells are removed less efficiently, increasing the risk of infection.
6. Why should antibiotics be taken for the full prescribed course?
Stopping antibiotics too early may leave some bacteria alive. These bacteria can multiply again and may become resistant to antibiotics, making future infections harder to treat.
7. Why does HIV weaken the immune system?
HIV attacks and destroys helper T cells (CD4 cells), which coordinate many immune responses. As these cells decrease, the body becomes vulnerable to opportunistic infections.
8. Why do allergies occur even when pollen or dust is not actually dangerous?
In allergies, the immune system mistakenly identifies harmless substances as dangerous and releases chemicals such as histamine, producing symptoms like sneezing, itching, and swelling.
9. Why can transplanted organs sometimes be rejected?
The recipient's immune system recognizes proteins on the transplanted organ as foreign antigens and attacks them. Immunosuppressant medicines are used to reduce this response.
10. Why does inflammation cause redness, heat, swelling, and pain?
During inflammation, blood vessels widen and become more permeable. Increased blood flow brings immune cells to the injured area, while fluid leaks into tissues, causing swelling and pain.
11. Why do tonsils often become enlarged during a throat infection?
Tonsils contain large numbers of lymphocytes that trap and destroy pathogens entering through the mouth and nose. During infection, immune cells multiply inside the tonsils, causing them to swell.
12. Why can removing lymph nodes during cancer treatment cause swelling in an arm or leg?
Lymph nodes help drain excess tissue fluid. When they are removed, lymph cannot flow normally, causing fluid to accumulate in tissues. This condition is called lymphedema.
13. Why is bone marrow considered one of the most important immune organs?
Bone marrow produces all blood cells, including white blood cells. It is also where B lymphocytes develop before entering the bloodstream.
14. A patient has a very low neutrophil count. What health problem are they most likely to experience?
Neutrophils are the body's first line of defense against bacteria. A low neutrophil count greatly increases the risk of bacterial infections.
15. Why do vaccines usually provide longer-lasting protection than antibody injections?
Vaccines stimulate the body's own immune system to produce antibodies and memory cells. Antibody injections provide only temporary passive immunity because no memory cells are formed.
16. Why do autoimmune diseases attack healthy body tissues?
In autoimmune diseases, the immune system fails to recognize the body's own cells and mistakenly attacks them as if they were harmful pathogens.
17. Why are fungal infections more common in people with weakened immune systems?
A weakened immune system cannot effectively control fungal growth, allowing fungi that are normally harmless to cause infections.
18. Why are macrophages often called the "clean-up cells" of the immune system?
Macrophages remove bacteria, viruses, dead cells, and cellular debris through phagocytosis, helping keep tissues clean while also activating other immune cells.
19. Why are complement proteins important even though they are not cells?
Complement proteins help destroy pathogens by damaging their cell membranes, attracting immune cells to the infection site, and marking microbes so they can be engulfed more easily.
20. Why do doctors sometimes prescribe immunosuppressant drugs after an organ transplant?
Immunosuppressant drugs reduce the activity of the immune system, preventing it from attacking and rejecting the transplanted organ while allowing it to function normally.
