Biology Eduqas Immunology and disease

What are natural barriers

Defences that are always present and are the same for all organisms

Describe the specific immune response

Second line of defence against pathogens that triggers foreign antigens

Two types: humoral immune response and cell-mediated immune response

What are T-lymphocytes

Lymphocytes that mature in the thymus gland

What are B-lymphocytes

Lymphocytes that are produced in the bone marrow and mature in the spleen and lymph nodes

Outline the process of the cell-mediated response

Complementary T lymphocytes bind to foreign antigens on antigen-presenting cell. T cells undergo colonal expansion.Three main types of T-lymphocytes produced: T killer cells, T helper cells and T memory cells

Explain the role of antigen-presenting cells

• Macrophage (phagocyte) displays antigen from pathogen on its surface (after hydrolysis in phagocytosis)

• Enhances recognition by T helper cell, which cannot directly interface with pathogens/antigens in body fluid

• Secrete cytokines that are involved in stimulating specific immune response

What are T effector cells

• T killer cells or cytoxic T lymphocytes

• Causes lysis of damaged or infected cells

Role of T helper cells

• Regulate immune response through the release of cytokines

• Cytokines stimulate the proliferation of B lymphocytes

Describe the role of T memory cells

Stay dormant until the host comes in contact with antigen again

Remain in blood and provide immunological memory

Outline the process of humoral immune response

1. Complementary T helper lymphocytes bind to foreign antigen on antigen-presenting T cells

2. Cytokines released that stimulate clonal expansion of complementary B lymphocytes

3. B lymphocytes differentiate into plasma cells

4. Plasma cells secrete antibodies with complementary variable region to antigen. Antibodies destroy the pathogen

Describe the structure of an antibody

• Y shaped

• Two light chains bonded to two longer heavy chains

• Two binding sites

• Specific to a particular antigen

Describe the primary and secondary immune responses

Primary immune response- initial response when a pathogen is first encountered. A small amount of antibodies are produced slowly

Secondary immune response- pathogen encountered for a second (third, fourth…etc) time. Immunological memory gives a rapid production of a large number of antibodies.

What is happening during the latent period of the primary immune response

• Antigen-presenting cells carry out phagocytosis

• T helper cells detect antigens and secrete cytokines

• Proliferation and differentiation of specific B and T cells

Define active immunity

Resistance in an organisms that has developed through the production of specific antibodies in response to a pathogen

It provides long-lasting immunity as memory cells are produced

What are the two types of active immunity

Natural active immunity- production of antibodies by the immune system following infection

Artificial active immunity- production of antibodies by the immune system following the exposure to a weakened, attenuated, or dead pathogen

Give an example of artificial active immunity

Vaccination against rubella

How do vaccinations that produce antigens provide long-lasting immunity?

• Antigens in vaccine trigger primary immune response without infection

• If pathogen is encountered, the secondary immune response destroys pathogen before symptoms develop

Define passive immunity

Resistance in an organism acquired via the transfer of antibodies

Provides short term immunity as no memory cells are produced

Two types of passive immunity

Natural- mothers antibodies passed to the foetus through the placenta and milk

Artificial- foreign antibodies are injected

Example of artificial passive immunity

Treatment of rabies

How do vaccinations that use antibodies provide short term immunity

• Antibodies provide rapid protection against a harmful microorganism

• Allows time for the development of an active immune response

Describe the different levels of effectiveness of vaccination programmes against different diseases

• Single round of vaccinations protects against pathogens that have low levels of antigenic variation/mutation eg Rubella

• Repeated vaccinations used against pathogens that have various antigenic types and mutate frequently, eg Influenza

Outline the ethical considerations that must be considered when designing vaccination programmes

• Cost of developing vaccine

• Effectiveness of vaccine

• Rights of individual vs rights of entire population to be protected

• Possible side effects

• Religious concerns

• Testing on animals and unaffected individuals

What does the natural skin flora do as a natural barrier

Prevent pathogenic bacteria colonising the skin surface by outcompeting them

What does the skin and connective tissue do as a natural barrier

skin is a tough, physical barrier; vitamin C is needed to maintain strong connective tissue

What is localised inflammation and how does it act as a natural barrier

It occurs at sites of damage where there are localised breaks in physical barriers (e.g., skin or mucous membranes).
It helps to prevent infection by:

• Increasing blood flow (vasodilation)

• Allowing white blood cells to reach the site

• Promoting phagocytosis and healing

• Containing the infection to stop it spreading

What is phagocytosis and how does it act as a natural barrier to infection?

When phagocytes engulf and destroy pathogens.

How does blood clotting act as a natural barrier to infection?

Platelets and clotting factors cause blood to clot in damaged blood vessels. This prevents blood loss and forms a barrier that stops pathogens entering wounds.

How do lysozymes act as a natural barrier to infection?

Lysozyme is an enzyme that kills bacteria by breaking down their cell walls. It is found in tears, saliva, and mucus, including in the stomach lining.

How does the ciliated epithelium act as a natural barrier to infection?

Ciliated epithelial cells line mucous membranes and trap microbes in mucus from inhaled air. The cilia move the mucus out of the airways to prevent infection.

What are the natural barriers to infection in the body

Tears, skin, large intestine, saliva, respiratory tract stomach and bladder

How are tears a natural barrier to infection?

wash away irritating substances and microbes

lysozyme kills many bacteria

How is skin a natural barrier to infection?

provides a physical barrier to the entrance of microbes

acidic pH discourages the growth of organisms

sweat, oil, and fatty acid secretions kill many bacteria

How is the large intestine a natural barrier to infection?

normal bacteria inhabitants keep invaders in check

How is saliva a natural barrier to infection?

washes microbes from the teeth and mucous membranes of the mouth

How is the respiratory tract a natural barrier to infection?

mucus traps organisms

cilia sweep away trapped organisms

How is the stomach a natural barrier to infection?

acid kills organisms

How does the bladder act as a natural barrier to infection?

urine washes microbes from urethra

Examples of bacterial infection

Cholera, Tuberculosis

Examples of viral infections

Influenza, smallpox

Give an example of a protoctistan infection

Malaria

What is cholera

Disease cause by strands of gram negative bacterium, Vibrio Cholerae, the toxins of which cause severe diarrhoea leading to dehydration

How is cholera treated

Rehydration (fluid and electrolytes)

Antibiotics

Source of infection and mode of transmission for cholera

contaminated water and food; faecal/ oral transmission

What is tuberculosis

A bacterial disease, caused by Mycobacterium tuberculosis and M. Bovis, that damages lymph nodes in the lungs and neck, and weakens the immune system

Source of infection and mode of transmission for tuberculosis

airborne droplet transmission

Methods of tuberculosis prevention and treatment

Prevention- BCG vaccination of children

Treatment- extensive course of antibiotics

What is smallpox

A disease caused by the virus Variola major that affects the skin and multiple other organs

Source of infection and mode of transmission for smallpox, variola major

droplet transmission and bodily fluids

Symptoms of smallpox

Headache, fever and pockmarking of the skin

How has smallpox been eradicated

A successful vaccination program

What properties of the smallpox virus made the eradication possible

Little variation in antigens

Low rate of antigenic mutation

Immunogenic nature of antigens

No animal reservoir

Source of infection and mode of transmission for influenza

droplet transmission contaminated surfaces

What tissue is affected by influenza

Upper respiratory tract

Symptoms for influenza

Headache, fever, sneezing and coughing, vomiting, sore throat, muscular and joint pain

May cause secondary bacterial infections

How is influenza treated

Quarantine, antiviral medication, antibiotics treat secondary bacterial infections, management of symptoms eg painkillers

Name the malarial parasite

Plasmodium spp.

Source of infection and mode of transmission for Malaria

Bites of female mosquitoes carrying plasmodium

Parasite reproduces asexually in red blood cells in liver, causing lysis

Describe the effects of Malaria on an infected individual

Causes recurrent episodes of fever and can be fatal

How is endemic Malaria controlled

Preventing mosquito bites- mosquito nets, insect repellent

Controlling mosquito numbers- pesticides, chemical treatment of standing water and sewage and introduction of predators for mosquitoes

Drug treatment

What is a pathogenic organism

An organism that has the ability to cause damage to a host

What is an infectious diease

Disease that can be transmitted between individuals

Define carrier

An infected individual that is asymptomatic but can spread the disease.

What is the disease reservoir

The environent (host) in which an infectious pathogen is found

Define endemic

A disease that is ever-present in an area

Define epidemic

A rapid rise in the incidence of a communicable disease at a local or national level

What is a pandemic

An epidemic that occurs worldwide, affecting a large number of individuals

Define vaccination

The deliberate exposure of an individual to non-pathogenic forms, antigens or products of pathogens to provide artificial active immunity

What is an antibiotic

substance produced by microorganisms that affects the growth of other microorganisms

What is an antigen

Chemical present on the surface of a cell that induces an immune resonse

Define antibodies

Immunoglobulins (antibodies) produced by B-lymphocytes in response to a specific antigen, triggering an immune response

What are antibiotic-resistant bacteria

Bacteria that mutate to become resistant to an antibiotic, survive and reproduce very rapidly, passing on their antibiotic resistance

Define vector

A living organism that trasmits a disease from one organism to another

What is a toxin

a poisonous substance produced by microorganisms that damages their host

What are antigenic types

Organisms that possess the same or similar antigens on their surface eg strains of bacteria

How are antigenic types usually identified

Using antibodies from serum

What is a host

The organism from which a pathogen or parasite obtains nutrients and/or shelter

Define viruses

non-living infectious agents that invade host cells and takeover cell metabolism, replicating within them

Outline the forms that the pathogenicity of viruses can take

Cell lysis

Cell transformation

Production of toxins

Immune system suppression

What is cell lysis

Disruption of cell membranes, destroying the cell

Virions released

Describe cell transformation

Viruses can stimulate healthy cells to become cancerous

Give an example of a virus that suppresses the immune system of a host

HIV

State the two types of antibiots

Bactericidal and bacteriostatic

How do bacteriostatic antibiotics work?

Prevent bacteria from multiplying; interfere with processes required for their growth such as metabolism or DNA replication, the infection doesn’t spread and the hosts immune system kills the bacteria

What are bactericidal antibiotics?

Kill bacteria directly

What is a narrow-spectrum antibiotic

Only effective against a narrow range of bacteria usually gram-positive

What is a broad-spectrum antibiotic

Effective against a wide range of bacteria

What are bacterial cell walls made up of?

A 3D mesh of peptidoglycan, a polymer of amino acids and sugars

Define gram-positive bacteria

Bacteria that have a thick peptidoglycan wall and a purple appearance following gram staining

Define gram-negative bacteria

Bacteria that have a thin peptidoglycan wall with an outer lipopolysaccharide membrane and a red appearance following gram staining

What type of antibiotic is penicillin

Narrow-spectrum antibiotic

Describe how penicillin affects bacteria

Kills gram-positive bacteria and damages gram-negative bacteria

Prevents the formation of cross-links between molecules in the peptidoglycan wall, so when osmotic changes occur, the cell undergoes lysis

How does penicillin prevent the formation of cross-links in the peptidoglycan wall

Transpeptidase catalyses the formation of cross-links in the peptidoglycan wall

Penicillin is a competitive inhibitor of transpeptidase

Why doesn’t penicillin kill gram-negative bacteria

Gram-negative bacteria do not completely lose their cell wall due to the presence of an outer lipopolysaccharide membrane

What type of antibiotic is tetracycline

Broad-spectrum antibiotic

Describe the effect of tetracycline in bacteria

Inhibits translation during protein synthesis

Competitive inhibitor of an anticodon-binding site on the 30S ribosomal subunits, preventing the formation of new proteins

Why do antibiotics not affect viruses

They do not have metabolic pathways

Why are some bacteria resistant to treatment by antibiotics

1. Random genetic mutation, often on plasmid, confers resistance eg antigen shape changes

2. These bacteria have selective advantage in the presence of antibiotics, reproduce and pass allele for resistance to offspring

3. Directional selection results in resistant strain