Cell recognition and the Immune System

Question 1

What’s an infection

Answer 1

interaction between the pathogen and the bodies defence mechanisms

Question 2

What’s immunity

Answer 2

Having overwhelmed the pathogen the body’s defences seem to be better prepared for a second infection from the same pathogen and can kill it before it causes any harm

Question 3

Defence mechanisms

Answer 3

Longer lasting responses involve a type of white blood cell called a lymphocyte and take two forms:

• cell mediated responses involving T lymphocytes
• humoral responses involving B lymphocytes

Question 4

Recognising your own cells

Answer 4

To defend the body, lymphocytes must be able to distinguish the body’s own cells (self) from those that are foreign (non-self)
- each cell, self or non self has specific molecules on its surface that identify it, they may have proteins on its surface, proteins have variety and tertiary structure. it’s the variety of specific 3-D structure that distinguish one cell from another
These protein molecules which usually allow the immune system to identify:
- pathogens e.g HIV
- non self material such as cells from other organisms of the same species
- toxins including those produced by certain pathogens
- abnormal body cells such as cancer cells
> specific lympocytes are not produced in response to an infection but they already exist

Question 5

Stages in recognising

Answer 5

1) identification in removing the threat they pose
2) immune system recognises these as non self even though they have come from individuals of the same species
3) it attempts to destroy the transplant

Question 6

When destroying the pathogen

Answer 6

the lymphocyte will most likely have a protein on the surface that’s complementary to one of the proteins of the pathogen

Question 7

Clonal selection

Answer 7

one type of lymphocyte already present that has complementary proteins to those of the pathogen is stimulated to divide to build up its numbers to a point where it can be effective in destroying it

Question 8

How lymphocytes recognise cells belonging to the body

Answer 8

• in the fetus, lymphocytes are constantly colliding with other cells
• some of the lymphocytes will have receptors that exactly fit those of the body’s own cells
• These lymphocytes either die or are suppressed
• no clones of these anti-self lymphocytes will appear in the blood, leaving only those that might respond to non- elf antigens

Question 9

two types of white blood cell

Answer 9

phagocytes and lymphocytes

Question 10

Phagocytosis

Answer 10

• chemicals of pathogens or dead cells act as attractants causing phagocytes to move towards the pathogen
• phagocytes have several receptors on their cell surface membrane that recognise and attach to chemicals on the surface of the pathogen
• they engulf the pathogen to form a vesicle known as phagosome
• lysosomes move towards the vesicle and fuse with it
• lysozymes are present within the lysosome. they destroy ingested bacteria by hydrolysis of cell walls
• the soluble products from the breakdown of the pathogen are absorbed into the cytoplasm of the phagocyte

Question 11

Antigens

Answer 11

foreign proteins that stimulate an immune response

• Antigens are part of cell surface membranes on invading cells
• presence of an antigen triggers the production of an antibody as part of the defence system

Question 12

Lymphocytes

Answer 12

• phagocytosis is a non specific response
• the body has specific responses that react to specific antigens, they’re slow but provide long term immunity
• Lymphocytes are produced by stem cells in the bone marrow and there are two types of Lymphocytes:
• B Lymphocytes (B cells) are associated with humoral immunity involving antibodies that are present in body fluids or ‘humour’ such as blood plasma
• T Lymphocytes they’re present in thymus gland. There associated with cell mediated immunity

Question 13

T Lymphocytes can distinguish these invader cells from normal cells

Answer 13

• phagocytes that have engulfed and hydrolysed a pathogen present some of a pathogen’s antigens on their own cell surface membrane
• body cells invaded by a virus present some of a viral antigens on their own cell surface membrane
• transplanted cells from individuals of the same species have different antigens on their cell surface membrane
• cancer cells are different from normal body cells and present antigens on their cell surface membranes

Question 14

cells that display foreign antigens on their surface are called

Answer 14

antigen-presenting cells

Question 15

What response is when T Lymphocytes will only respond to antigens that are presented on a body cell

Answer 15

Cell mediated or cellular response

Question 16

The role of receptors on T cells

Answer 16

• the receptors on each t cell respond to a single antigen

Question 17

Stages in response of T Lymphocytes to infection by a pathogen

Answer 17

• pathogen invade body cells
• phagocyte places antigen from the pathogen on its cell surface membrane
• receptors on a specific helper T cell fit exactly onto these antigens
• The attachment of T cell to divide rapidly by mitosis and form a clone of genetically identical cells
• The cloned T cells:
  > develop into memory cells that enable a rapid response
  > stimulate phagocytes to engulf pathogens by phagocytosis
  > stimulate B cells to divide and secrete their antibody
  > activate cytotoxic T cells

Question 18

How cytotoxic T cells kill infected cells

Answer 18

• they kill abnormal cells and body cells that are infected by pathogens
• producing a protein called perforin that make holes in the cell surface membrane
• the holes mean the membrane become freely permeable and cell die as a result
• The action of T cells is most effective against viruses because viruses replicate inside cells

Question 19

Humoral Immunity

Answer 19

• involves antibodies and they’re soluble in the blood and tissue fluid

Question 20

A clone produces

Answer 20

• one specific antibody these antibodies are referred to as monoclonal antibodies

Question 21

Plasma cells

Answer 21

• Plasma Cells: secrete antibodies into blood plasma. These antibodies lead to the destruction of the antigen. The plasma cells are responsible for the immediate defence of the body. The production of antibodies and memory calls is known as the primary immune response

Question 22

Memory Cells

Answer 22

responsible for the secondary immune response. Memory cells live longer than plasma cells

• When they encounter the same antigen, they divide rapidly and develop into plasma cells and more memory cells
• memory cells provide long term immunity against the original infection

Question 23

B cell in humoral immunity

Answer 23

1) The surface antigens of an invading pathogen are taken up by a B cell
2) B cell processes the antigens and presents them on its surface
3) Helper T cells attach to the processed antigen on the B cell and activating it
4) The B cell is not activated and is dividing by mitosis
5) Cloned plasma cells produce and secrete the specific antibody that exactly fits the antigen on the pathogens surface
6) The antibody attaches to antigens on the pathogen and destroys them
7) Some b cells develop into memory cells. These can respond to future infections by dividing. This is the second

Question 24

Antibodies

Answer 24

Antibodies are proteins with specific binding sites synthesised by B cells

• antibody binding sites are complementary to a specific antigen
• antibodies are made up of four polypeptide chains
• each antibody has a specific binding site that fits precisely onto a specific antigen to form an antigen-antibody complex
• each binding site consists of a sequence of amino acids that form a specific 3-D shape that binds directly to a specific antigen
• The rest of the antibody is known as the constant region
• This binds to receptors on cells such as B cells

Question 25

How the antibody leads to the destruction of the antigen

Answer 25

• they prepare the antigen for destruction
  Antibodies assist in its destruction in two ways:
• They cause agglutination of the bacterial cells are formed making it easier for the phagocytes to locate them
• they serve as markers that stimulate phagocytes to engulf the bacterial cells to which they attach

Question 26

Monoclonal antibodies

Answer 26

• each antigen will induce a different B cell to multiply and form a clone itself. Each of these clones will produce a different antibodies. these are known as monoclonal antibodies

Question 27

Targeting medication to specific cell types by attaching a drug to an antibody

Answer 27

As an antibody is very specific to a particular antigen, monoclonal antibodies can be used to target specific substances and specific cells. they can target cancer cells
Monoclonal antibody therapy:
- monoclonal antibodies are produced that are specific to antigens on cancer cells
- these antibodies are given to a patient and attach themselves to the receptor on their cancer cells
- They attach to the surface of the cancer cells and block the chemical signals that stimulate their uncontrolled growth

Question 28

Herceptin

Answer 28

a monoclonal antibody used to treat breast cancer. an adv of direct monoclonal therapy is that antibodies aren’t toxic and are highly specific

Question 29

Medical diagnosis

Answer 29

• they’re used for the diagnosis of influenza, hepatitis and chlamydia
• men with prostate cancer often produce more of a protein called prostate specific antigen

Question 30

Pregnancy testing

Answer 30

• The kits rely on the fact that the placenta produced a hormone called human chlorionic gonadatrophin and this is found in the mother’s urine.
• Monoclonal antibodies present on the test strip of a home pregnancy testing kit are linked in colour particles
• if hCG is present in the urine it binds to these antibodies
• the hCG- antibody colour complex moves along the strip until it is trapped by a different type of antibody created a coloured line

Question 31

Ethical use of monoclonal antibodies

Answer 31

• the production involves the use of mice and they’re used to produce both antibodies and tumour cells
• monoclonal antibodies have been used successfully to treat a number of diseases, including cancer and diabetes

Question 32

Passive Immunity

Answer 32

• no direct contact with pathogen or its antigen to reduce immunity
• immunity is acquired immediately
• no memory cells are formed and so there is no lasting immunity
• e.g passive immunity include anti venom given to the victims of snake bites and the immunity acquired by the fetus when antibodies pass across the placenta from the mother

Question 33

Active immunity

Answer 33

is produced by stimulating the production of antibodies by the individuals own immune system
- Direct contact with the pathogen or its antigen is necessary
> Natural active immunity: results from an individual becoming infected with a disease under normal circumstances. The body produces its own antibodies and may continue to do so for many years
> Artificial active immunity: forms the basis of vaccination. it involves introducing an immune response in an individual

Question 34

Vaccinations

Answer 34

• the intention is to stimulate an immune response against a disease
• a vaccine contains one or more types of antigen from the pathogen

Question 35

Herd Immunity

Answer 35

herd immunity arises when a large proportion of the population has been vaccinated

Question 36

Why vaccination may not eliminate a disease

Answer 36

• Vaccination fails to induce immunity in certain individuals, for example people with defective immune systems
• some may develop the disease immediately after vaccation but before their immunity levels are high enough to prevent it
• antigenic variability: mechanism by which an infectious agent such as a protozoan, bacterium or virus alters its surface proteins in order to avoid a immune response.
• individuals may have objections to vaccination for religious, ethical or medical reasons

Question 37

The ethics of using vaccines:

Answer 37

• they have side-effects that may sometimes cause long term harm
• To be fully effective the majority of population should be vaccinated
• how can individual health risks from vaccination be balanced

Question 38

Structure of HIV

Answer 38

• on the outside is a lipid envelope embedded with attachment proteins
• inside the envelope is a protein layer called the capsid which holds two single strands of RNA
• one enzyme is reverse transcriptase so it catalyses the production of DNA to RNA

Question 39

Replication of HIV

Answer 39

it can’t replicate itself unless its in a living host cell
It does this by:
- HIV enters the bloodstream and circulates the body
- CD4 the protein binds to the protein on HIV. HIV attaches to helper T cells
- protein capsid fuses with cell surface membrane and RNA and enzymes of HIV enter helper t cell
- HIV reverse transcriptase converts RNA to DNA
- The newly made DNA is moved into the helper t cell’s nucleus where it’s inserted into cells DNA
- HIV DNA in nucleus creates messenger RNA using cells enzymes. mRNA contains info to make new proteins and RNA go into new HIV
- mRNA passes out of nucleus through nuclear pore and uses the cells protein synthesis to make HIV particles
- HIV particles break away from helper T cell with a piece of its cell surface membrane surrounding them which forms their lipid envelope

Question 40

How HIV causes

Answer 40

HIV is a virus that affects the human immune system. It eventually leads to AIDS
AIDS is a condition where the immune system deteriorates and eventually fails. Someone with aids is more vulnerable to other infections like pneumonia.

Question 41

intial infection

Answer 41

During the initial infection period, HIV replicates rapidly and the infected person may experience severe flu-like symptoms
Latency period: HIV replication drops to a lower level
During the latency period the infected person won’t experience any symptoms.

Question 42

Symptoms of AIDS

Answer 42

• Minor infections of mucous membranes (e.g inside of the nose, ears and genitals) and recurring respiratory infections
• As AIDS progresses the number of immune system cells decreases further~ patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and tuberculosis

Question 43

Antibiotics on HIV/ AIDS

Answer 43

• Antiviral drugs can be used to slow down the progression of HIV infection and AIDS
• Antibiotics kill bacteria by interfering with their metabolic reactions. They target the bacterial enzymes and ribosomes. Antibiotics are designed to only target the bacterial ones so they don’t damage human ones
  Viruses don’t have their own enzymes and ribosomes- they use the ones in the host cells. Human viruses use human enzymes and ribosomes to replicate, antibiotics can’t inhibit them. Most antiviral drugs are designed to target the few virus-specific enzymes that exist