Module 4

Active immunity

Resistance in an organism that has developed through the production of

specific antibodies in response to a pathogen. It provides long-lasting immunity as memory

cells are produced.

Agglutinins

Chemicals that cause pathogens to aggregate together, aiding phagocytosis.

Antibodies can act as agglutinins.

Antibiotic

A chemical or compound produced by a living organism that kills or prevents the

growth of bacteria.

Antibiotic-resistant bacteria

Bacteria that mutate to become resistant to an antibiotic,

survive and reproduce very rapidly, passing on their antibiotic resistance.

Antibodies

Immunoglobulins produced by B-lymphocytes in response to a specific antigen,

triggering an immune response.

Antigen

A chemical present on the surface of a cell that induces an immune response.

Antigen-presenting cell

A macrophage that displays foreign antigens.

Anti-toxins

Chemicals produced by white blood cells that neutralise toxins released by

pathogens.

Artificial active immunity

The production of antibodies by the immune system following the

exposure to a weakened, attenuated or dead pathogen, e.g

by vaccination.

Artificial passive immunity

The immunity acquired from the administration of specific

antibodies from another organism, e.g

by vaccination.

Athlete’s foot

A form of ringworm in humans that affects the feet, resulting in cracking and

scaling of the skin.

Autoimmune disease

A condition in which the immune system attacks and destroys

healthy body tissue, e.g

arthritis, lupus.

Bacteria

Prokaryotic cells that have cell walls but lack organelles. Some bacteria are

pathogenic, producing toxins that damage host cells.

Bacterial meningitis

A severe form of meningitis caused by bacterial infection of the

meninges. Complications of bacterial meningitis include septicaemia; a symptom of this is a

rash of purple discolouration that does not fade when a glass is pressed against it.

B effector cells

A type of B lymphocyte that divides to form plasma cells.

Black sigatoka

A fungal disease in tomatoes caused by Mycosphaerella fijiensis , the

hyphae of which penetrate and digest host leaf cells, turning them black.

B lymphocytes

Lymphocytes that mature in the bone marrow. There are three main types;

plasma cells, B effector cells and B memory cells.

B memory cells

B lymphocytes that provide immunological memory.

Callose

A plant polysaccharide that contains β-1,3 and β-1,6 linkages between glucose

molecules. It is deposited between the cell walls and cell membrane in cells adjacent to

infected cells, serving as a defence against pathogens. It is also found in the cell walls of

infected cells and the plasmodesmata between infected cells.

Chitinases

Enzymes that degrade chitin in fungal cell walls.

Clonal expansion

The mass proliferation of specific antibody-producing cells.

Clonal selection

The identification of an antibody-producing cell with complementary

receptors to the shape of a specific antigen.

Clostridium difficile

A type of bacteria found in the gut of some individuals which is

resistant to most antibiotics.

Communicable disease

A disease that is caused by a pathogen and transmitted directly

between organisms.

Cytokines

Cell-signalling molecules produced by mast cells in damaged tissue. They attract

white blood cells to the site of damage.

Direct transmission

The transfer of a pathogen directly from one organism to another. This

can occur via direct contact, ingestion or the sharing of contaminated needles.

Epidemic

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

level.

Expulsive reflexes

Coughs or sneezes initiated upon irritation of the respiratory tract. They

remove microorganism-containing mucus from the gaseous exchange system.

Fungi

Eukaryotic, often multicellular organisms that may cause disease. They digest and

destroy cells, and produce spores that can spread rapidly between organisms.

Glucanases

Enzymes produced by plants that decompose glucans, polysaccharides found

in oomycete cell walls.

Histamine

A chemical produced by mast cells in damaged tissue. It makes blood vessels

dilate and causes their walls to become leakier.

Human Immunodeficiency Virus (HIV)

An infectious virus that destroys T helper cells,

weakening the immune system of the body. HIV makes an individual more susceptible to

opportunistic infections and can lead to AIDS (Acquired Immunodeficiency Syndrome).

Indirect transmission

The transfer of a pathogen indirectly between organisms via fomites,

vectors, droplet infection or soil contamination.

Inflammation

A localised response of vascular tissue to pathogens, damage or irritants. It is

characterised by pain, redness, heat and swelling.

Influenza

A common viral infection caused by the family of viruses, Orthomyxoviridae, that

destroys ciliated epithelial cells in the gaseous exchange system, exposing the airways to

secondary infection.

Interleukins

Cytokines produced by T helper cells that stimulate B cells.

Lymphocytes

White blood cells that contribute to the specific immune response.

Lysosome

A membrane-bound organelle that contains hydrolytic enzymes.

Malaria

A disease caused by the protoctista Plasmodium that lives within two hosts,

mosquitoes and humans. It causes recurrent episodes of fever and can be fatal.

Mast cells

Specialised cells in connective tissue that are important in the inflammatory

response, releasing histamines and cytokines.

MRSA

A type of bacteria that is resistant to the antibiotic methicillin.

Mucous membranes

The membranes lining body cavities that secrete a sticky mucus.

Natural active immunity

The production of antibodies by the immune system following

infection.

Natural passive immunity

The immunity acquired by an infant mammal when antibodies

are transferred through the placenta and the colostrum from the mother.

Non-specific defences

Defenses that are always present and are the same for all

organisms, e.g

skin, blood clotting, inflammation, mucous membranes and expulsive

reflexes.

Opsonins

Chemicals that bind to and tag foreign cells, making them easily recognisable to

phagocytes.

Passive immunity

Resistance in an organism acquired via the transfer of antibodies. It

provides short-term immunity as no memory cells are produced.

Pathogen

A disease-causing microorganism. Includes bacteria, viruses, fungi and

protoctista.

Penicillin

The first conventional, effective and safe antibiotic derived from the mould

Penicillium chrysogenum . It was discovered by Alexander Flemming.

Personalised medicine

A form of medical care that enables doctors to provide healthcare

that is customised to an individual's genotype.

Phagocytes

Specialised white blood cells that engulf and destroy pathogens. There are two

types

neutrophils and macrophages.

Phagocytosis

The process by which phagocytes engulf and destroy pathogens.

Phagolysosome

A vesicle within a phagocyte formed by the fusion of a phagosome and