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Human Immune Responses

www.user.gwdg.de/~hbruegg/ct/start.htm

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What is a pathogen?

• Any disease -producing agent. – Non-cellular agents

• Prions, viruses, viroids

– Cellular agents• Bacteria, eukaryotes

http://www.bio.miami.edu/ecosummer/lectures/lec_symbiosis.html

http://kenyonfarrow.com/tag/african-americans/

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A bit of history• The Black Death killed about a third of

Europe’s population, between 1347 and 1351. But it was not until 1894 that the pathogen (a bacterium) that caused the plague was identified.

• Scientists showed that fleas escaping from dead infected rats carried the bacterium to humans.

• So, 550 years earlier, not knowing anything about bacteria, the population had no idea about the control and prevention of the disease.

• They used masks, closed all door and windows to keep the wind out, attacked foreigners and people of different religions and whipped each other believing it was God’s punishment.

http://bcm.bc.edu/issues/spring_2008/linden_lane/close-up.html

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A bit of history

• Before biologists such as Louis Pasteur discovered bacteria and other pathogens people had many strange ideas about preventing and controlling diseases.

• Ignaz Semmelweis (a Hungarian doctor) insisted that doctors washed their hands in a chlorine solution before examining pregnant women. This procedure greatly reduced “childbirth fever” and the deaths of women in childbirth.

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A bit of history

• Malaria is a tropical disease that affects millions of people worldwide. The term malaria originates from Mediaeval Italian: mala aria — “bad air“. It used to be called marsh fever due to its association with swamps and marshland.

• What’s the association?

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A bit of history

• The influenza pandemic of 1918 - 1919 (Spanish Flu)(H1N1) killed between 20 – 40 million people (12,000 in Australia).

• Today 250,000 to 500,000 die annually worldwide. Most of these are people over 65.

• Today: Avian flu (H5N1) and Swine flu (H1N1). Pandemic??

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What is an antigen?

A protein, toxin, or cellular or non-cellular agents, to which the body reacts by producing antibodies. The exception being prions.

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Membrane receptors

• These are glycoproteins (MHCs) that are unique to individuals.

• They allow the body’s immune system to distinguish between SELF and NON-SELF.

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Major Histocompatibility Complex (MHC) proteins

• MHC proteins occur on the membranes of all nucleated cells.

• These enable the system to ensure that “self” cells are not destroyed by the immune system.

http://commons.wikimedia.org/wiki/File:TCR-MHC_bindings-tr.png

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MHC markers

• Class 1 markers are on the membranes of all nucleated cells (not RBCs)

• Class 2 markers are on membranes of B cells, T cells and some macrophages.

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Non-self

• Proteins or toxins (antigens) that have NOT been produced by the body are recognised as non-self.

• Such proteins that belong to pathogens initiate a series of reactions – the immune response – which are responsible for the destruction and removal of the invader.

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Non-specific immunity

• First line of defence–skin

–mucous membranes

–natural secretions

–natural flora

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Non-specific immunity

• Second line of defence– phagocytes– Natural Killer (NK) cells– complement proteins– interferon– cytokines– inflammation

– clotting

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Non-specific immunity

http://www.uic.edu/classes/bios/bios100/lecturesf04am/lect23.htm

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Specific immunity

• Third line of defence– B cells – humoral (antibody-mediated)

response• Plasma cells antibodies (immunoglobulins)• memory B cells

– T cells – cell-mediated response• helper T (CD4+) cells• cytotoxic T (CD8+) cells• memory T cells

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The lymphatic system• The lymphatic system is

essential to both the circulatory and immune systems.

• The lymph nodes drain fluid from most of our tissues. They are an immunological filter where the immune responses mostly occur.

• Antigens are filtered out of the lymph in the lymph node before returning the lymph to the circulation.

www.naturalhealthschool.com/8_4.html

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B and T cells

• B and T cells are lymphocytes.

• All lymphocytes are produced in bone marrow.

• B cells mature in the bone marrow.

• T cells mature in the thymus.

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B cells and antibodiesEach B cell contains multiple copies of one kind of antibody as a surface receptor for antigen. The entire population of B cells has the ability to specifically bind to millions of different antigens.

When a B cell is matched with its specific antigen two reactions are triggered:

– plasma cell proliferation• Antibody (monoclonal antibodies)

production – memory B cell production

This process is called clonal selection.

The production of antibodies by B cells is called HUMORAL IMMUNE RESPONSE.

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B plasma cells

Since antibodies are proteins, B plasma cells have a massive protein manufacturing infrastructure. Note the:– rough ER– Golgi bodies– mitochondria

http://cytochemistry.net/Cell-biology/

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Antibodies

• Antibodies are specific for each different antigen.

• This specificity occurs at the variable portion of the antibody.

• The disulphide bonds allow the chains to move apart (like a hinge) to enable them to capture and accommodate the antigen.

http://science.kukuchew.com/tag/immunoglobulin/

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Antibody response

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T cells – cell mediated response• Cells that present an antigen

on their cell membranes are called antigen presenting cells (APCs).

• Macrophages engulf attacking pathogens.

• Some of pathogens’ surface proteins (antigen) are added to macrophages’ membranes.

• Helper T (Th) cells recognise these proteins (antigens) as non-self as well as the macrophages class 2 marker.

• Th cells secrete a protein, cytokine, that stimulates the cloning of B cells into plasma cells and memory B cells. They also stimulates the cloning of cytotoxic (Tc) cells into active Tc cells and memory T cells.

http://www.agen.ufl.edu/~chyn/age2062/lect/lect.htm

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T cells – cell mediated response

• Appropriate B cells then proliferate and produce antibodies for that specific antigen.

• Increased number of memory T cells are then circulating to reduce time in finding that pathogen.

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T cells – cell mediated response

• Cells that have been infected with a virus add part of the viral protein coat (antigen) to their membranes.

• Cytotoxic T (Tc) cells then recognise infected cells by the presence of the added antigen and the cells’ class 1 marker.

• Tc cells then release a protein that disrupt the infected cells’ membranes (lysis) and the cells then die before the viral particles have time to replicate.

• This process also happens with cancer cells and grafted cells.

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Immune response

http://www.biologycorner.com/

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http://www.biol.sc.edu/

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Acquired immunity

• Active – when antibodies are produced by a person– natural– induced

• Passive – when antibodies are received from an external source– natural– induced

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Acquired immunity

• Natural active immunity– when a person is infected by a pathogen and

the B cells produce antibodies. B and T memory cells are also produced.

• Induced/artificial active immunity– when a person is immunised against a

disease by vaccination. The body then produces antibodies primary antibody response.

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Acquired immunity

• Natural passive immunity – gives immediate protection– a foetus receives maternal antibodies across

the placenta.

• Induced passive immunity – also immediate– antibodies injected into a person.

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Plants and pathogens

• Mechanical barriers - similar to our skin– cuticle (waxy layer) of leaves– epidermal cells (including bark)

• Chemical barriers – similar to antibiotics– many plants produce chemicals that can ward

off or kill pathogens.• eg, the tobacco plant produces nicotine to kill

insects that eat its leaves.

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Control of diseases

• Quarantine– strict controls at points of entry into Australia

to ensure exotic diseases and pests are not allowed to enter.

• Departments of Health and Agriculture– maintain statistics and, therefore, awareness

of changes of disease patterns in humans and farm fauna and flora.

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Unit 3 Biology

Exams

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Examination time – 1½ hoursExamination time – 1½ hoursContribution to study score – Contribution to study score – 33%33%Approved materials and Approved materials and equipment – pencil to use on equipment – pencil to use on multiple-choice answer sheet.multiple-choice answer sheet.

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Students will be required to recall facts, definitions, and examples; explain biological concepts,principles and processes; apply understanding of these concepts to unfamiliar situations; analyserelationships; analyse and evaluate experimental procedures; and synthesise ideas.

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Total No. of marks: 75Total No. of marks: 75

Total No. of minutes: 90Total No. of minutes: 90

Time per mark: 1 min.Time per mark: 1 min.

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Examiners’ Report

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Most important in first few minutes

• Try and relax– this will help you focus

• Read the exam paper cover sheet– understand what the structure of the paper is and

what’s expected of you.

• Read through the paper– you’ll start to feel more relaxed – you’ll know the

answers to some of the questions.– you’ll probably find links between different questions

in different sections which may help you answer these questions.

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When you start writing

• Write your VCAA number on the paper – in numbers and words.

• Answer the questions that you know the answers to first. You can start anywhere in the paper. You’ll then feel more relaxed and ready to tackle the rest of the paper.

• If you’re stuck on a MC question then leave it for a while but mark the question so as not to forget to come back to it..

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During the exam

• Keep an eye on the time!– remember to try and keep to the pace of:

• ONE MARK = ONE MINUTE

• Multiple choice questions– read each question carefully– if you don’t know the answer try and eliminate

at least two of the distractors

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During the exam

• Short answer questions– Keep answers short and to-the-point– ‘1 mark’ usually means one point to make– ‘2 marks’ – two points

• Near the end of the exam you should have about 10 mins left. Have a look at your answers but do NOT change any answers on impulse. Think carefully!

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Overall • ENJOY doing the paper.

• Show the examiner what you know and feel good about doing it. You’ve worked hard to get to that point.