Biology- Cell Recognition

non-specific barriers

prevent pathogens from getting in- immediate and works for most pathogens

specific barriers

immune response to kill pathogens- slower and pathogen specific

non-specific barrier examples

skin, stomach, eyes, breathing system- physical barrier or phagocytes

specific barrier examples

Immune system: white blood cells, antitoxins, memory lymphocytes. Cell mediated or humoral response

Pathogen

A microorganism that causes disease

Infection

interaction or invasion of the body by a pathogenic organism. Cannot be killed by medication

immunity

the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.

2 options upon infection

1. pathogen overwhelms defences-\> death
2. defences overwhelm the pathogen-\>recovery

What must lymphocytes be able to do?

distinguish between self and non-self cells

what would happen if lymphocytes were unable to distinguish between self and non-self?

our immune system wouldn't combat pathogens and would destroy our own tissues

how can lymphocytes distinguish between pathogens and self-cells?

markers are present on cell surfaces

antigen

molecule on the surface of pathogens that triggers an immune response.

clonal selection

antigens bind to specific receptors, causing a fraction of lymphocytes to clone themselves

Why do we not want lymphocytes to be complementary to self cells?

Because the lymphocytes would attack self cells and leave our immune system weak

Lymphocyte production in adults

In the bone marrow

Apoptosis

programmed cell death

How does cell recognition impact transplant patients?

The organ may often get rejected as the lymphocytes see it as a non-self cell. This causes the person to be very ill due to the strong immune response so they have to take immunosuppressant drugs.

Immunosuppressant drugs

drugs which suppress the immune system of the recipient of a transplanted organ to prevent rejection

White blood cells

fight infection and combat pathogens

Types of WBC

Lymphocytes and Phagocytes

Phagocytes

White blood cells that attack invading pathogens, non-specific and travel in blood but can move out to other cells due to segmented nucleus

Phagocytosis

Process in which a pathogen is engulfed

Phagocytosis step 1

Pathogen releases chemoattractants and the phagocyte is attracted to them so moves towards the pathogen.

Phagocytosis step 2

Receptors on the phagocyte attach to chemicals on the pathogen surface.

chemoattractants

chemical signals and products of a pathogen

Phagocytosis step 3

formation of phagosome because the bacteria is engulfed. Lysosomes move closer to the phagosome

Phagocytosis step 4

Lysosomes fuse with the phagosome, and they release lysozymes (lytic enzymes) into the phagosome which hydrolyses the bacterium.

Phagocytosis step 5

The hydrolysis products of the bacterium are absorbed by the phagocyte. Antigens are presented on cell membrane of phagocyte

Purpose of presenting bacterium products

signals other areas of the immune system that there is an infection that they must fight & also they can produce antibodies.

Impact of pH change on immune response

could alter charges on the active site which break down pathogens so this could prevent pathogen hydrolysis.

What is a specific response?

A slower response that is specific to each pathogen

Advantage of specific response

Develops immunity in the long term

Disadvantage of specific response

Slower as it targets certain pathogens

Which cells are required to initiate a specific response?

Requires lymphocytes

T lymphocytes

cell-mediated immunity
Mature in thymus gland

What do t lymphocytes respond to?

Responds to foreign material inside body cells so it only responds if pathogen is directly affecting body cells

Antigen presenting cells

Cells that display foreign antigens on their surface

T cells and phagocytes

When phagocytosis occurs, the pathogen is engulfed by a phagocyte and displays antigens. This means the T cells can bind

T cells and body cells invaded by viruses

They would display the antigens of the virus to alert the body to the virus invasion. Acts as a distress signal

T cells and cancer cells

They are different from healthy cells as they present antigens on the surface

T cells and transplanted cells

These are bodily cells but look completely different because they come from elsewhere so they contain different antigens

cell mediated immunity stage 1

pathogen invades body cells/taken in by phagocytes or engulfed

cell mediated immunity stage 2

phagocyte presents pathogen's antigens on it's cell surface membrane

cell mediated immunity stage 3

receptors on specific helper T cells fit exactly onto antigens because they are complementary

cell mediated immunity stage 4

activates the T cell to undergo clonal selection (divide through mitosis)

4 things cloned T cells can do

develop into memory cells
stimulate the phagocytes
stimulate the B cells to divide
activate cytotoxic t cells

Cytotoxic T cells

attack abnormal body cells.
Produce a protein called perforin that makes holes in the cell surface membrane and make it a freely permeable membrane

Perforin

One of the proteins released by cytotoxic T cells on contact with their target cells. It forms pores in the target cell membrane that contribute to cell killing.

B lymphocytes

form in the bone marrow and release antibodies that fight bacterial infections, respond to foreign material outside body cells

How do T and B cells work together?

B cells find an antigen in the body and join with it to form an antigen-antibody complex. It is taken up through endocytosis.
B cells present the antigens on the surface and the T cells attach to B cells and help B to divide in clonal selection.

What happens in the second part of humoural immunity?

cloned B plasma cells produce specific antibodies for a quick response and they attach to the antigen of the pathogen and destroy it (primary response)

Humoural immunity

The type of response which involves B lymphocytes and antibodies.

what happens in the third stage of humoural immunity?

some B cells remain and become memory cells. They respond in the future and create the secondary response

Plasma cells

secrete antibodies into blood plasma but survive for only a few days. Part of primary response

Memory cells

live for decades, circulate in blood and tissue fluids. dont produce antibodies directly - divide into both plasma and memory cells for secondary response

Secondary immune response

memory cells facilitate a faster, more efficient response

Issues with memory cells?

Many pathogens have many cell surface proteins which acts as antigens and they can change and mutate meaning memory cells may not always recognise cells

Antigen variation

changing its appearance by altering surface antigens

Antibodies

Specialized proteins that aid in destroying infectious agents

antibodies

specialised proteins that aid in destroying infections (antigens or pathogens)

Where are antibodies found?

plasma cells

Describe the structure of an antibody in terms of protein hierarchy

They have a quaternary structure (3d shape and formed of many polypeptide chains). Two heavy polypeptide chains bonded to two light chains.

variable region of antibody

antigen binding site

constant region of antibody

terminal that contains 2 heavy chains; binds to receptors on cells

Explain why the Antibody will only detect a certain antigen (3 marks)

Antibody and it's variable region has a specific amino acid sequence
This gives a specific shape (tertiary structure) which is complementary to the antigens
It forms a complex between antigen and antibody

Do antibodies directly destroy antigens?

No they lead to antigen structure through other means

Agglutination

Clumping of microorganisms or blood cells, typically due to an antigen-antibody interaction. Easier for phagocytes to locate and engulf as they are less spread out

Markers (roles of antibodies)

Antibodies act as markers that stimulate phagocytes making it easier to engulf the pathogen

Monoclonal antibodies

Antibodies produced by a single clone of B lymphocytes and that are therefore identical in structure and antigen specificity. Single type. Often produced outside the body

Polyclonal antibodies

a series of antibodies are produced responding to a variety of different sites on the antigen. Produced from a variety of B cells

Monoclonal antibody therapy

A type of treatment by which monoclonal antibodies are administered, the antibodies form an antibody-antigen complex with cancerous cells which prevents further growth and stimulates chemical destruction of the cancer

Herceptin

Antibody for treating:
Ovarian Cancer
Breast cancer

What can Herceptin do?

Engulf cancer cells and mark them for destruction
Block the chemical signals that stimulate uncontrolled growth

Advantages of antibody therapy

Non-toxic
Highly specific

Indirect monoclonal antibody therapy

- a radioactive or cytotoxic drug is attached to a monoclonal antibody that is bound to antigens
Kills cancer cells

How do pregnancy tests work?

1) Monoclonal antibodies are used to detect human chorionic gonadotropin (hCG) found in the urine of a pregnant woman
2) When urine is applied to the application area, the antibodies bind to any hCG, forming antigen-antibody complexes
- these antibodies are attached to blue-coloured beads
3) The urine moves up to the test strip, where immobilised antibodies bind to any hCG antigen-antibody complexes
- the test strip turns blue from the concentration of coloured beads

What can antibodies identify?

Flu, hepatitis, cancer, chlamydia

ELISA test

Enzyme Linked Immunosorbent Assay uses antibodies to detect presence and quantity of a protein in a sample

1st stage of ELISA test

Apply sample to well surface.
Antigens in sample attach to surface
Wash to remove any unattached antigens

2nd stage of ELISA test

Add the antibody that is specific to the antigen we wish to detect.
Leave to allow binding then wash.

3rd stage of ELISA test

Add a second antibody to bind with the 1st. This one will have an enzyme attached to it. Wash again.

4th stage of ELISA test

Add substrate to enzyme (must be colourless)
This enzyme acts on substrate and causes a colour change for a positive result

ELISA positive result

Colour change

Ethical implications of monoclonal antibodies

Mice are used to test- animal cruelty
Deaths associated with use of monoclonal antibodies
Drug testing can impact even healthy people

Passive immunity

the short-term immunity that results from the introduction of antibodies from an outside source. No memory cells produced so it is short term but immediate.

Active immunity

production of antibodies stimulated by the individual. Requires direct contact with pathogen and takes time. Has 2 forms.

natural active immunity

production of one's own antibodies or T cells as a result of infection or natural exposure to antigen

artificial active immunity

Production of one's own antibodies or T cells as a result of vaccination against disease

Vaccines

A preparation that prevents a person from contracting a specific disease- contain small amounts of weakened or dead forms of a pathogen

When a vaccine is given to a person, it leads to the production of antibodies against a disease-causing organism. Describe how.

1. Vaccine contains antigen from pathogen;2. Macrophage presents antigen on its surface;3. T cell with complementary receptor protein binds to antigen;4. T cell stimulates B cell;5. (With) complementary antibody on its surface;6. B cell secretes large amounts of antibody;7. B cell divides to form clone all secreting / producing same antibody

Corona Virus vaccine

Developed a synthetic version of some of the virus' mRNA. Our cells read it as an instruction to start building spike proteins (antigens). The body then ammounts an immune response against them

How do you make a vaccination programme successful?

Cheap
Few side effects
Be able to produce, store and transport vaccines
Administer them correctly

Herd immunity

The resistance of a group to an attack by a disease to which a large proportion of the members of the group are immune

How do you achieve herd immunity?

Vaccinate large amounts of a population all at the same time

Why are vaccination programs rarely 100% successful?

Some people have defected immune systems
Pathogens can mutate and change their antigens
Pathogens have different strains
Some hide from immune systems
People object to vaccinations

Ethics of vaccinations

Production uses animals
Side effects
Who should be tested on?
Can people be forced to get a vaccine?
Should expensive vaccination programmes still continue if a disease is eradicated?

HIV

human immunodeficiency virus

AIDS

acquired immune deficiency syndrome

Impact of HIV/AIDS on immune system

Gradually destroys the sufferers immune system

How did HIV reach humans?

chimpanzees
Jumped the species barrier