immunity

What is a pathogen

Disease causing microorganisms

What are the four types of pathogens

• bacteria → produce toxins that damage the body

• Viruses →use host cells to replicate before bursting out and destroying our cells

• Protoctists → take over cells and break them open

• Fungi → digest living cells to destroy them and some produce toxins

Whats a non-specific defence mechanism

• act quickly to defend body

• Respond same way for all pathogens

• Second line of defence → invading pathogens are targeted by macrophages

Whats a specific defence mechanism/ response

• slower to defend body

• Produce specific response for each pathogen

• Second line of defence → Lymphocytes produce chemicals called antibodies that target specific pathogens

What are examples of non-specific defence mechanisms

• skin

• Mucous membranes

• Expulsive reflexes

• Blood cutting and wound repair

• Inflammation

• The nose

• Trachea and bronchi

• Stomach

How is the skin a non defence mechanism

• physical barrier to block out pathogens from entering body

• Chemical barrier by producing sebum, an antimicrobial, oily substance that lowers pH yo inhibit the growth of pathogens

How is mucous membranes a non specific barrier

• parts of the ears, nose, throat and digestive tract are lined by mucous membranes

• These membranes secrete mucous to trap pathogens and use lysosomes to destroy them

How are expulsive reflexes a non-specific defence barrier

• Coughing and sneezing are methods for expelling foreign objects from the gas exchange system

• Vomiting and diarrhoea expel the contents of the gut along with any pathogen present

How is blood clotting and wound repair a non specific defence barrier

• cut to skin provides entry for pathogen so blood clots to seal wound

• Clot dries out to form scab to block entry

• After scab has formed, skin is capable of repairing itself to reform skin (physical barrier) epidermal cells underneath scab divide while damaged blood vessels regrow and collagen fibres are used to provide strength to new tissue

• Once epidermis is the required thickness, the scab breaks off and wound is healed

How is inflammation a non-specific defence barrier

Inflammation consists of swelling, heat, redness and pain at site of infections and wounds. It can be triggered by damaged tissues which release chemicals affecting blood in two ways

• blood vessels dilate which increased blood flow to this area, making it hotter to prevent pathogens from reproducing

• Blood vessel wall become more permiable sp they start to leak tissue fluid, causing swelling and isolating any pathogen in damaged tissue

Whats an antigen

• proteins molecule found on the surface of cells thats recognised as foreign by the immune system

How are antigens a specific defense system

Antigens allow immune system to recognise various cells and molecules

• pathogens → immune system recognises as foreign and activates cells to destroy pathogen

• Abnormal body cells → cancer versus or infected cells display abnormal antigens that activate an immune response

• Toxins → these are antigen molecules (not cells) and can be recognised by the immune system

• Cells from other organisms of the same species → these cells may have different antigens to body’s own cells and so identified as foreign. This causes rejection of transplants

What are the steps of specific defence

1. Phagocytosis → Phagocytes absorb and ingest the pathogen

2. Antibodies → lymphocytes release antibodies. They are complimentary to antigens on pathogen. The antibodies bind ton the antigen and cause the pathogen to burst

3. Antitoxins → when bacteria enters your body they release toxins. Body releases antitoxins to destroy toxins

What ways can disease be spread

most infections are communicable and need to enter through a body opening

• vectors → living organisms which transfer microbes

• Fomites → inanimate object e.g towel

• Direct contact → skin to skin/ bodily fluids

• Inhalation → breathing in

• Indigestion → consuming it on food

• Inoculation → through broken skin

What are the steps of phagocytosis

• phagocyte tracks pathogen

• Phagocyte binds to pathogen

• Phagocyte engulfs pathogen

What is phagocytes

• phagocyte is a type of white blood cell that performs phagocytosis

• Phagocytosis is a non-specific defence mechanism where phagocytes engulf and destroy pathogens → has same response for all pathogens

• Located in blood and body tissue

• Two types, neutrophils and macrophages

Whats a neutrophil phagocyte

• rapid responders

• Rush to site of infection to engulf pathogen

What are macrophages

• engulf pathogens

• Can also present pathogens antigens on their surface

• Helps activate other immune cells

Kept stages of phagocytosis

1. Pathogens release chemicals attracting phagocytes to site of infection

2. The phagocyte recognises the pathogens antigens as non-self. This causes the phagocyte to bind to the pathogen

3. The phagocyte engulfed the bacterium to form a phagosome

4. Lysosomes ,move towards phagosome and fuse with it

5. Hydrolytic enzymes released by lysosomes digest bacterium

6. Soluble products from the breakdown of the pathogen are absorbed into cytoplasm

7. Antigens from bacteria are displayed in phagocyte cell membrane

What are the two types of specific defence mechanisms

• cellular respiration

• Humoral response

The type of specific immune response depends on a type of white blood cell known as a lymphocyte

What’s re the two types of lymphocytes

• T lymphocytes or T cells → T cells mature in the thymus gland. They are involved in the cellular response where they respond to antigens presented on body cells

• B lymphocytes or B cells → B cells mature in the bone marrow. They are involved in the humoral response where they produce antibodies found in the body fluids

What are helper T cells

• These cells have receptors on their cell surface that bind to complimentary antigens on antigen-presenting cells.

• After binding, they can form memory cells, stimulate B cells or phagocytes, and activate cytotoxic T cells

Cytotoxic T cells

• these kill abnormal and foreign cells by producing a protein called perforin → this protein makes holes in cell-surface membrane, causing it to become freely permeable and causing cell death

Memory T cells

• these cells provide long-term immunity against specific pathogens. They provide a rapid response if the body is re-infected by the same pathogen

Whats a cellular response

When T cells only respond to antigens presented on body cells rather than antigens within body fluid

What are the steps of cellular response

1. Phagocytes engulf pathogens and display antigens on the cell surface. They are now known as antigen-presenting cells

2. Helper T cells with complimentary receptors bind to these antigens

3. On binding, helper T cell is activated to divide by mitosis to form genetically identical clones

What functions do the cloned T cells carry out

• develop into memory cells - these circulate in the body to provide long term immunity

• Stimulate phagocytosis - cloned cells stimulate phagocytes to engulf pathogens

• Stimulate division of B cells - cloned cells stimulate B cells to divide and produce antibodies

• Activate cytotoxic T cells - this allows cytotoxic T cells to kill infected cells

What is the humoral response

• protects body from disease

• Involves production of specific antibodies to destroy pathogens

• Use of B lymphocytes or B cells produce abd are covered in proteins known as antibodies

• Antibodies found in body fluids

What cells are involved in humoral response

• B cells

• Plasma cells

• Memory cells

• Helper T cells

What are B cells

• cells have antibodies on cell surface membrane that bind to complimentary antigens

• Engulf antigens and display them on their cell-surface to become antigen-presenting cells

• Once activated, B cells can divide into plasma cells and memory cells

What are plasma cells

• type of B cells that can produce and secrete antibodies against a specific antigen

• They have a short lifespan of only a few days

What are memory cells

• types of B cell that provide long-term immunity against specific pathogens

• Much longer life span than plasma cells

• They rapidly divide into plasma cells if the body is re-infected by same pathogen

What are helper T cells

• cells that bind antigen-presenting cells to activate division of B cells

Whats the difference between clonal selection and colonial expansion

• colonial selection - B cell with correct antibody is selected for cloning (by being activated by a T helper cell)

• Colonial expansion - The division of specific B cells to produce genetically identical clones

What are the two types of immune responses

• primary immune response → when body is exposed to pathogen for the first time. Response is low and infected individual experiences symptoms

• Secondary immune response → when body has been exposed to same pathogen as before. Repose is much faster and pathogens destroyed before any symptoms appear

What is the primary immune response

1. Production of antibodies is low after first exposure to pathogen

2. Concentration of antibodies increase slowly

3. This due to very few B cells specific to pathogens antibody

4. Takes time for B cells to divide into plasma cells to produce correct antibody, so individual experiences symptoms of disease Takes

5. Some B cells divide into memory cells to make individual immune

What is the secondary response

1. Production of antibodies is much quicker after exposure of pathogen

2. Concentration of antibodies increases quickly

3. This is because memory cells recognise pathogens antigens and quickly divide into plasma cells

4. These plasma cells secrete larger numbers of antibodies to quickly destroy the pathogen before the individual experiences any symptoms

What’s the structure of an antibody

• y shaped, glycoproteins m,ade up of 4 poly peptide chains.

• 4 poly peptide chains → 2 heavy chains and two light chains

• Poly peptide chains held together by disulphide bridges

• Made up if 2 regions → constant region and variable region

Whats the constant region

• same for all antibodies

• Binds to receptors on calls such as B cells

Whats the variable region

• different for each antibody as shape is complimentary to specific antigen

• Part of antibody that binds to antigen

How does the antigens shape effect its binding to antigens

• antibody co plimentary active site to specific antigen.

• Forms antibody- antigen complex

What’s the functions of antibodies

• agglutination of pathogens

• Neutralisation of toxins

• Preventing pathogens from binding

Whats agglutination of pathogens

• antibodies act as agglutinins, causing pathogens to clump together. This makes it easier for phagocytes to locate pathogens and allows them to engulf a number of pathogens at once

Whats neutralisation of toxins (antobodies)

Antibodies act as antitoxins when they bind to toxins o produced by pathogens. This binding neutralises toxins to prevent them from damaging body cells

How are pathogens prevented from binding to cells

Antibodies block pathogens antigens, they block cell-surface receptors needed to bind to host cells. This means pathogen cannot bind to or invade host cells

What are monoclonal antibodies

• antobodies produced from a single clone of plasma cells

• Each antibody was identical to one another so will bind to a specific molecule

What are the uses of monoclonal antibodies

• diagnosis of disease → monoclonal antibodies bind to specific cell types to identified infected cells

• Treatment of disease → monoclonal antibodies bind to specific cells, bringing therapeutic drugs to them

• Pregnancy testing → monoclonal antibodies bind to a pregnancy hormone

• Detecting cancers → monoclonal antibodies can bound to a specific cancer antigen to identify types of cancer

What are ELISA tests

• The enzyme-linked immunoSorbant Assay (ELISA) tests use monoclonial antibodies to detect both the presence and quantity of protein in a sample.

• It’s often used to find out if a patient has antigens for a pathogen and hence has the disease

What are the two types of ELISA tests

1. Direct test - uses only one antibody

2. Indirect test - uses two antibodies

What are the steps of the ELISA tests

1. Add sample (containing target protein) to a well plate where the target protein can attach well

2. Add antibody thats specific to target protein. These antibodies bind to target proteins attached to the well plate

3. Wash well to remove unbound antibodies

4. Add a second antobodies that binds to first antibody. The secondary antibodies attached to an enzyme

5. Wash well again to remove any unbound secondary antibody

6. Add a solution containing substrate to well. The enzyme attached to secondary antibody will act on substrate to cause colour change. Intensity of colour indicates quantity of protein present

Whats active immunity

• Develops when immune system makes its own antibodies after exposure to pathogens antigens

• Takes a while too become immune but has long term protection because memory cells are produced

What’s passive immunity

• when individual is given antobodies made by a different organism

• Provides immediate immunity to the disease, but it is short erm protection because antibodies are broken down and memory cells are not produced

What are vaccines

1. Contain antigen from pathogen

2. Macrophages present those antigens on its surface

3. T-cell with complimentary receptors proteins bind to antigen

4. T cells stimulate b cells with complimentary antibodies on its surface

5. B cells (plasma cells) secrete large amounts of antibodies

6. B cells divide to form clones, all secreted from the same antibody

What are ethics of vaccines

• human testing required → could result in side effects

• Deciding who should take priority when pandemic comes

• Due to herd immunity not everyone has to have vaccine. Some may deem this as unfair

• Tested on animals first

Difference between active and passive immunity

• active involves memory cells, passive doesn’t

• Active involved production of antibodies by plasma or memory cells

• Passive involves antibodies from another organism

• Active is long term as antibody produced in response to antigen

• passive is short term as antibody is broken down

• Active slow passive fast

Where are lymphocytes (white blood cells) produced

Bone marrow

Whats herd immunity

• When a large population is vaccinated, those who aren’t vaccinated are also protected

Whats is structure of HIV

• genetic material → 2 single strands of RNA

• Enzymes → one of these enzymes reverse transcriptase which allows virus to convert RNA into DNA

• Capsid → layer of protein molecules that surrounds and protects genetic material

• Envelope → outer layer of phospholipids

• Glycoproteins → help virus bind to host cells

How does HIV replicate

• uses T helper cells to replicate

1. Attachment proteins on HIV attach to receptors on helper T cell

2. HIV releases RNA into help T cells

3. Reverse transcriptase converts this RNA into DNA

4. Viral DNA inserted into helper T cells genome

5. helper T cells DNA translated to make viral proteins

6. Proteins used to assembly new HIV particles

7. Fully assembled HIV particles leave cell in order to infect other cells