Immune System

Question 1

What are lymphocytes and what are their functions

Answer 1

Your Body’s immune system has cells to identify the presence of pathogens and potentially harmful foreign substances in the body and to then destroy or neutralise them to prevent harm. These cells are lymphocytes

Question 2

How can lymphocytes distinguish between pathogens and self-cells?

Answer 2

Each type of cell has specific molecules on its surface that identify it. These mcolules are usually proteins as their 3D tertiary structure enables lots of unique and identifiable shapes to be made

Question 3

How does the immune system recognise things that don’t belong in the body, and what kinds of things can it recognise?

Answer 3

Cells have surface molecules (antigens) on them
• Your immune system recognises your own antigens → no reaction
• If a cell has different antigens → it is recognised as non-self
• This triggers an immune response to destroy it
E.g:
1. Pathogens (e.g. bacteria, fungi or viruses such as HIV)
2. Cells from other organisms of the same species (harmful or those with organ transplants)
3. Abnormal body cells (e.g. cancer cells)
4. Toxins (some pathogens release toxins in the blood (e.g. cholera)

Question 4

What are antigens and where are they located

Answer 4

Antigens are foreign proteins that generate an immune response by lymphocyte cells when detected in the body.
They are located on the surface of cells

Question 5

Explain antigen variability

Answer 5

Pathogens DNA can mutate frequently. If a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change. Any previous immunity to this pathogen (either naturally through prior infection or artificially through vaccination) is no longer effective, as all the memory cells in the blood will have a memeory of the old antigen shape. This is known as antigen variability. This is known as antigen variability. The influenza virus mutates and changes its antigen very quickly and this is why a new flu vaccine has to be created each year.

Question 6

What are the barriers in the immune response

Answer 6

Is a pathogen gets last the chemical and physical barriers (e.g. skin and stomach acid) and enters the blood then the white blood cells are the second line of defence

Question 7

What type of response is do phagocytes and lymphocytes have ?

Answer 7

Phagocytes: non-specific
Lymphocytes: specific

Question 8

What is a phagocyte and where are they found:?

Answer 8

A phagocyte is a macrophage (type of white blood cells) that carries out phagocytosis
They are found in the blood and in tissues

Question 9

Describe phagocytosis

Answer 9

Phagocytosis is a non-specific response. Any non-self cell (e.g. pathogen) that is detected will trigger the same response to destroy it

Question 10

Explain phagocytosis step by step

Answer 10

1.Phagocytes are in the blood and tissues and any chemicals or debris released by pathogens or abnormal cells attract the phagocytes and they will move towards these cells.
2. There are many receptor binding points on the surface of phagocytes. They will attach to chemicals or antigens on the pathogen via these receptors.
3. The phagocyte changes shape to move around and engulf the pathogen.
4. Once engulfed the pathogen is contained with a phagosome vesicle.
5. A lysosome within the phagocyte will fuse with the phagosome and release its contents.
6. The lysozyme enzyme is released into the phagosome. This is a lytic enzyme which hydrolyses the pathogen.
7. This destroys the pathogen.
8. The soluble products are absorbed and used by the phagocyte

Question 11

What are lymphocytes and where are they made

Answer 11

Lymphocytes are white blood cells involved in the specific immune response
All lymphocytes are made in the bone marrow, but T cells mature in the thymus

Question 12

What does the cell mediated response involve

Answer 12

The cell mediated response is the response involving T cells and body cells

Question 13

What are antigen presenting cells and give examples

Answer 13

Antigen presenting cells (APC)
any cell that presents a non-self antigen on their surface:
Infected body cells will present the viral antigens on their surface
A macrophage which has engulfed and destroyed a pathogen will present the antigens on their surface
Cells of a transplanted organ will have different shaped antigens on their surface compared to your self-cell antigens
Cancer cells will have abnormal shaped self-cell antigens

Question 14

Explain the cell mediated response

Answer 14

1. Once a pathogen has been engulfed and destroyed by a phagocyte, the antigens are positioned on the cell surface.
   This is now called an antigen presenting cell (APC)
2. Helper T cells have receptors on their surface which can attach to the antigens on APC.
3. Once attached this activates the helper T cells to divide by mitosis to replicate and make large numbers of clones
4. Cloned helper T cells differentiate into different cells
   • Some remain as helper T cells and activate B lymphocytes
   • Some stimulate macrophages to perform more phagocytosis
   • Some become cytotoxic T cells (killer T cells)

Question 15

What are cytotoxic T cells

Answer 15

Cytotoxic T cells destroy abnormal or infected cells
They release a protein, perforin, which embeds in the cell surface membrane and makes a pore (a hole) so that any substance can enter or leave the cell surface membrane
This causes the cell death
This is most common in viral infections because viruses infect body cells
Body cells are sacrificed to prevent viral replication
This is why you get a sore throat when you have a cold the cytotoxic T cells detour the infected body cells in your throat

Question 16

What is the humoral response

Answer 16

The humoral response is the response involving B cells and antibodies.
Antibodies are soluble and transport in bodily fluids, ‘humour’ is an old term for body fluids, hence the name humoral response

Question 17

Explain B cell activation

Answer 17

There are approximately 10 million different B cells which are have antibodies on their surface complementary to 10 million different antigens.
Antigens in the blood collide with their complementary antibody on a B cell.
. The B cell
takes in the antigen by endocytosis and then presents it on it’s cell surface membrane.
When this B cell collides with a helper T cell receptor, this activates the B cell to coal expansion and siterentiation (clonalugr selection)
B cells undergo mitosis to make large numbers of cells, these differentiate into plasma cells or memory B cells.
Plasma cells make antibodies
B memory cells can divide rapidly into plasma cells when re-infected with the sáme pathogen to make large numbers of antibodies rapidly.

Question 18

What are memory B cells

Answer 18

Memory B cells can live for for decades in your body, whereas plasma cells are short lived
Memory B cells do not make antibodies, rather they will divide by mitosis and make plasma cells rapidly if they collide with an antigen they have previously encountered
This results in large numbers of antibodies being produced so rapidly that the pathogen is detoured before any symptoms can occur

Question 19

What are antibodies

Answer 19

Quaternary structure protein
Variable regions (bind to different shaped antigens
Constant regions (same in every antibody
Light chain
Heavy chain
Antigen binding sites

Question 20

Explain agglutination

Answer 20

Antibodies are flexible and can bind to multiple antigens to clump them together
This makes it easier for phagocytes to locate and destroy the pathogens
Form antigen-antibody complex
They don’t kill the antigen they make it efffieicent for phagocytosis

Question 21

Explain passive immunity

Answer 21

Antibodies are introduced into the body
The pathogen doesn’t enter the body so plasma cells and memory cells are not made
No long-term immunity
e.g antibodies passed to a fetus through the placenta or through breast milk to a baby

Question 22

Explains active immunity

Answer 22

Immunity created by your own immune system following exposure to the pathogen or its antigen

Natural active immunity:
Following infection and the creation of the bodies own antibodies and memory cells

Artificial active immunity:
Following the introduction of a weakened version of the pathogen or antigens via a vaccine

Question 23

Explain vaccination

Answer 23

A weakened or dead pathogen is introduced into the body.
Phagocytes engulf the pathogen by phagocytosis and present the antigens on their surface.
T helper cells with complementary receptors bind to the and become activated.
The activated T helper cells divide by mitosis to produce clones of T cells.
B cells with complementary receptors bind directly to the antigen and are activated (with help from T helper cells).
The B cells undergo clonal expansion and differentiate into plasma cells and memory B cells.
Plasma cells produce specific antibodies which bind to the antigen forming antigen–antibody complexes.
Memory cells remain in the body, producing a faster and larger secondary response if exposed to the pathogen again.

Note VERY IMPORTANT:

1️⃣ “T cells differentiate into B cells”

This is wrong.
T cells and B cells are different lymphocytes — one does NOT turn into the other.

Correct idea:
• Helper T cells activate B cells.
• B cells then divide and differentiate.

⸻

2️⃣ Antigen–antibody complex & agglutination timing

Agglutination happens after plasma cells produce antibodies, not when B cells first bind antigen on a phagocyte.

Also:
• B cells bind directly to free antigen, not antigen on a phagocyte.
• T cells recognise antigen presented on phagocytes.
• B cells recognise antigen directly.

—> Phagocytosis
→ APC
→ Activates T helper cell
→ B cell binds complementary antigen
-> B cell presents the antigen on its surface
→ T helper cell binds to B cell
→ activated T cells activate B cells

Question 24

Explain Herd immunity

Answer 24

If enough of the population are vaccinated the pathogen cannot spread easily amongst the population

This provides protection for those who are not vaccinated e.g. those who already too ill to have a vaccine, or those who are too young

Question 25

Explain HIV’s structure

Answer 25

HIV is a retrovirus with a lipid envelope derived from the host cell membrane. This envelope contains glycoproteins which are crucial for the virus to attach to and enter host cells. HIV consists of four key structures: 1. Core = genetic material (RNA) and the enzyme reverse transcriptase, which are needed for viral replication. 2. Capsid = outer protein coat. 3. Lipid envelope = extra outer layer made out of lipids taten from the host's cell membrane. 4. Protein Attachments = on the exterior of the envelope to enable the virus to attach to the host's helper T cell.

Question 26

Explain the replication of HIV in replication in helper T cells

Answer 26

HIV is transported around in the blood until it attaches to a CD4 protein on the helper T cells. The HIV protein then fuses with the helper T cell membrane, enabling the RNA and enzymes from HIV to enter. The HIV enzyme reverse transcriptase copies the viral RNA into a DNA copy and moves to the helper T cell nucleus, this is why it is called a retrovirus. Here mRNA is transcribed, and the helper T cell starts to create viral proteins and these are assembled to make new viral particles. 🦠 Step-by-Step Explanation of How HIV Infects a Cell 1️⃣ Attachment (Finding the Target) HIV travels through the blood until it finds a specific immune cell called a helper T cell (CD4 cell). • Helper T cells have a protein on their surface called CD4. • HIV has proteins on its outer surface that recognize and bind to CD4. • This is like a key (HIV) fitting into a lock (CD4). ⸻ 2️⃣ Fusion (Getting Inside the Cell) After attaching: • The outer membrane of HIV fuses with the membrane of the helper T cell. • This allows HIV to release its contents into the cell. • Inside are: • Viral RNA (its genetic material) • Special enzymes (including reverse transcriptase) ⸻ 3️⃣ Reverse Transcription (RNA → DNA) Here’s the unusual part: • Most living cells use DNA → RNA → Protein. • HIV is different because it carries RNA instead of DNA. The enzyme reverse transcriptase: • Converts the viral RNA into DNA. • This is why HIV is called a retrovirus (“retro” means backward). ⸻ 4️⃣ Integration (Hiding in the Nucleus) • The newly made viral DNA enters the nucleus of the helper T cell. • It inserts itself into the cell’s own DNA. • Now the cell can’t tell the difference between its own genes and the viral genes. The virus is now basically “hiding” inside the cell’s genetic material. ⸻ 5️⃣ Transcription & Translation (Making Viral Parts) Because the viral DNA is now part of the cell’s DNA: • The cell makes mRNA from the viral DNA. • The cell’s ribosomes read that mRNA. • Viral proteins are produced. • New copies of viral RNA are also made. The cell is now being used as a virus factory. ⸻ 6️⃣ Assembly & Release (New Viruses Form) • Viral RNA + viral proteins assemble into new HIV particles. • These new viruses leave the cell. • They go on to infect more helper T cells. ⸻ 🧠 Why This Is Dangerous Helper T cells are extremely important because they: • Coordinate the immune response • Help fight infections

Question 27

Explain AIDS

Answer 27

HIV specifically targets and destroys helper T cells, which activate B cells. As the number of helper T cells decreases, the immune system becomes weaker, making the body more susceptible to infections and diseases. This results in immunodeficiency, where the body no longer has an effective immune response. This results in AIDS (Acquired Immunodeficiency Syndrome), where individuals become vulnerable to opportunistic infections and cancers. Symptoms of AIDS: chronic infections, weight loss, fever, and night sweats appear. These are often followed by more serious illnesses like pneumonia, tuberculosis, and certain cancers. HIV positive is when a person is infected with HIV. AIDS is when the replicating viruses in the helper T cells interfere with the normal functioning of the immune system.

Question 28

Explain Monoclonal antibodies

Answer 28

A monoclonal antibody is a single type of antibody that can be isolated and cloned. Antibodies are proteins which have binding sites complementary in shape to certain antigens. • •• Antigens Antigen z Antigen-binding site (varible) This has been manipulated to create monoclonal antibodies for: Light poly-peptide chain Medical treatment Heavy poly-peptide chain Medical diagnosis Antibody Pregnancy tests

Question 29

Explain targeted medication specifically direct monoclonal antibody therapy:

Answer 29

Some cancer can be treated using monoclonal antibodies which are designed with a binding site complementary in shape to the antigens on the outside of cancer cells. The antibodies are given to the cancer patient and attach to the cancer cells. While the antibodies are bound to the cancer antigens, this prevents chemicals binding to the cancer cells which enable uncontrolled cell division Therefore, the monoclonal antibodies prevent the cancer cells growing, and as they are designed to only attach to cancer cells they do not cause harm to other normal cells.

Question 30

Explain targeted medication specifically indirect monoclonal antibody therapy

Answer 30

Cancer can also be treated with monoclonal antibodies complementary in shape to the antigens on the outside of cancer cells which have drugs attached to them. The cancer drugs are therefore delivered directly to the cancer cells and kill them. This reduces the harmful side effects that traditional chemotherapy and radiotherapy can produce. This is often referred to as 'bullet drugs'

Question 31

What can monoclonal antibodies be used to test for

Answer 31

Monoclonal antibodies can be used to test for: - pregnancy - influenza - hepatitis - Chlamydia - prostate cancer e.g. Covid 19 antibody test This works via an ELISA test

Question 32

Explain the ELISA TEST step by step

Answer 32

Add the test sample from a patient to the base of the beaker. 2. Wash to remove any unbound test sample. 3. Add an antibody complementary in shape to the antigen you are testing the presence of in the test sample. 4. Wash to remove any unbound antibody. 5. Add a second antibody that is complementary in shape to the first antibody and binds to the first. The second antibody has an enzyme attached to it. And wash to remove any unbound antibody which has the enzyme attached 6. The substrate for the enzyme, which is colourless, is added. This substrate produces coloured products in the presence of the enzyme. 7. The presence of the colour indicates the the intensity of ane elour indicates ample and quantity present.

Question 33

What are the ethical issues involved in monoclonal antibodies

Answer 33

Creating monoclonal antibodies requires mice to produce the antibodies and tumour cells, which leads to ethical debates as to whether this use of animals is justified to enable the better treatment of cancers in humans and to detect disease.