Cell Recognition And The Immune System Flashcards
(33 cards)
What is an infectious disease and what causes it?
Infectious disease: Caused by pathogens — bacteria, viruses, fungi.
How does the immune system protect the body?
The immune system protects the body from these threats using specialised white blood cells
What is an antigen?
Antigen is a molecule (often protein) on a surface of a pathogen that triggers an immune response when detected by the immune system.
Where can antigens be found?
On the surface of pathogens, abnormal body cells (e.g. cancer), toxins, and cells from other individuals (e.g. transplants).
Describe the process of phagocytosis.
- Phagocyte detects foreign antigens on pathogen.
- Cytoplasm engulfs the pathogen → forms phagocytic vacuole.
- Lysosome fuses with vacuole → releases lysozymes → digests pathogen.
- Phagocyte presents antigens on surface → becomes antigen-presenting cell (APC).
Phagocytosis begins when a phagocyte recognises and binds to foreign antigens on the surface of a pathogen. The phagocyte then engulfs the pathogen by surrounding it with its cytoplasm, forming a phagocytic vacuole. A lysosome fuses with this vacuole and releases lysozymes, which hydrolyse the pathogen’s components and break it down. The phagocyte then presents the pathogen’s antigens on its surface, becoming an antigen-presenting cell (APC).
What is a T-cell and what is its role?
A T-cell is a type of white blood cell with receptor proteins that bind to complementary antigens on Antigen presenting cells.
• Helper T-cells: Activate B-cells.
• Cytotoxic T-cells: Kill abnormal or foreign cells.
How do B-cells respond to antigens?
- Antibodies on B-cell bind to complementary antigen.
- Helper T-cell activates B-cell → clonal selection.
- B-cell divides into plasma cells.
- Plasma cells produce monoclonal antibodies specific to the antigen.
B-cells have antibodies on their surface that bind to complementary antigens on pathogens. This antigen-antibody binding, along with stimulation from a helper T-cell, activates the B-cell — a process known as clonal selection. The activated B-cell then divides by mitosis to produce a clone of identical cells, including plasma cells. These plasma cells secrete large quantities of monoclonal antibodies that are specific to the original antigen.
What is the structure of an antibody and how does it help?
• Variable regions: Bind to specific antigens.
• Constant regions: Same in all antibodies.
• Two binding sites allow agglutination of pathogens → enhances phagocytosis.
Antibodies have variable regions at the ends of their two arms, which are specific and complementary to antigens — allowing them to bind effectively. The constant region is the same in all antibodies and allows attachment to immune system cells such as phagocytes. Each antibody has two antigen-binding sites, enabling it to bind to two pathogens at once, causing them to clump together (agglutination). This enhances phagocytosis by making it easier for phagocytes to engulf multiple pathogens at once.
Describe the difference between the primary and secondary immune responses.
• Primary response is Slow, symptoms occur, memory cells produced.
• Secondary response is Faster, stronger, no symptoms → memory cells rapidly produce plasma cells and antibodies.
The primary immune response occurs when the body is exposed to an antigen for the first time. It is slow because there are no memory cells, so the body takes time to activate B and T cells and produce antibodies. As a result, symptoms often develop during this time. However, memory cells are produced.
The secondary immune response happens upon re-exposure to the same antigen. It is faster and stronger, as memory B and T cells are quickly activated. This leads to a rapid production of plasma cells and antibodies, so the pathogen is destroyed before symptoms occur.
What is the structure of an antibody and how does it help?
• Variable regions: Bind to specific antigens.
• Constant regions: Same in all antibodies.
• Two binding sites allow agglutination of pathogens → enhances phagocytosis.
What is vaccination and how does it work?
Vaccination is the Introduction of antigens (free or attached to weakened/killed pathogen) to produce memory cells without causing disease. Prevents future infection.
What is herd immunity?
Heard immunity is when most of the population is vaccinated, the spread of disease is reduced → protects those who are unvaccinated.
Herd immunity occurs when a large proportion of the population is vaccinated, which reduces the overall spread of a disease. As a result, unvaccinated individuals are less likely to come into contact with the pathogen, so they are indirectly protected.
Compare active and passive immunity.
Active immunity requires exposure to an antigen, whereas passive immunity does not.
Active immunity develops slowly because the immune system takes time to respond, while passive immunity provides immediate protection.
Memory cells are produced in active immunity, leading to long-term protection.
In contrast, passive immunity does not produce memory cells, so the protection is short-term as the antibodies are eventually broken down.
What is antigenic variation and how does it affect immunity?
Pathogen changes surface antigens → memory cells don’t recognize → must undergo primary response again → leads to repeated infections (e.g. flu).
Antigenic variation is when a pathogen changes its surface antigens. As a result, memory cells from a previous infection no longer recognise the pathogen. This means the immune system must carry out a primary response again, which is slower and allows symptoms to develop. Antigenic variation can lead to repeated infections, such as with the influenza virus.
What are monoclonal antibodies and how are they used?
Monoclonal antibodies Identical antibodies from one B-cell clone. Used in:
• Targeting cancer drugs to tumor antigens (fewer side effects)
• Pregnancy tests: Detect hCG hormone using antibodies bound to blue beads.
Monoclonal antibodies are identical antibodies produced from a single clone of B-cells. They are specific to one antigen.
They are used in:
• Targeted cancer treatment: Monoclonal antibodies can be attached to anti-cancer drugs and designed to bind to antigens (e.g. tumor markers) on cancer cells. This ensures the drug is delivered directly to the cancer cells, reducing damage to healthy cells and limiting side effects.
• Pregnancy tests: Monoclonal antibodies are used to detect the hormone hCG in urine. These antibodies are attached to coloured particles (often blue beads) and produce a visible line if hCG is present.
How does HIV cause AIDS?
- HIV infects T-helper cells by binding to specific receptors on their surface.
- Inside the cell, HIV’s RNA is reverse transcribed into DNA by the enzyme reverse transcriptase.
- The viral DNA is integrated into the host cell’s genome, where it remains dormant or is used to produce new viruses.
- Over time, HIV replicates and destroys more T-helper cells, severely reducing their number.
- With too few T-helper cells, the immune system becomes weakened, and the body is unable to fight off opportunistic infections — this stage is called AIDS (Acquired Immune Deficiency Syndrome).
Why don’t antibiotics work on viruses like HIV?
Viruses use host cells to replicate → no metabolic pathways or cell walls for antibiotics to target.
Antibiotics do not work on viruses like HIV because viruses replicate inside host cells and do not have their own metabolic pathways or cell walls. Antibiotics target structures like bacterial cell walls or ribosomes, which viruses lack, so they are ineffective against viral infections.
What is an infectious disease and what causes it?
“Infectious disease: Caused by pathogens — bacteria, viruses, fungi.”
How does the immune system protect the body?
“The immune system protects the body from these threats using specialised white blood cells.”
How do cellular and humoral responses interact?
The cellular and humoral responses interact through the action of helper T cells (TH cells). When activated by antigen-presenting cells, TH cells stimulate B cells, which are part of the humoral response. The B cells then differentiate into plasma cells that produce antibodies. These antibodies bind to antigens on pathogens, tagging them for destruction. This enhances phagocytosis by phagocytes, linking the cellular and humoral arms of the immune system.
Define active immunity and give its two types.
“Active Immunity: is when the immune system is exposed to a new antigen triggering an immune response producing its own memory cells and antibodies specific to the antigens for long-term protection
Types:
• Natural active immunity – develops after catching a disease.
• Artificial active immunity – develops after receiving a vaccine containing a harmless form of the antigen.
Define passive immunity and give its two types.
“Passive Immunity: Immunity from receiving antibodies made by another organism. Provides immediate protection but is short-term
Types: • Natural passive immunity – when antibodies are transferred from mother to baby via the placenta or breast milk.
• Artificial passive immunity – when antibodies are injected into a person (e.g., for tetanus treatment) to provide immediate protection.
What are the steps of a direct ELISA and how is a positive result indicated?
the test for a direct ELISA
1. Antigens from the patient sample are bound to the surface of a well in a microtiter plate.
2. An enzyme-linked antibody that is specific to the antigen is added and allowed to bind.
3. After washing away any unbound antibody, a substrate is added. A colour change in the well indicates a positive result, confirming the presence of the target antigen.
Define passive immunity and give its two types.
“Passive Immunity: Immunity from receiving antibodies made by another organism. Types: Natural — from mother’s antibodies via placenta and breast milk; Artificial — injection of antibodies (e.g., tetanus treatment).”
