Active immunity: Immunity developed through production of antibodies in response to the antigens of a pathogen.

Agglutinin: Antibodies that cause pathogens to clump together.

Antibiotic: A chemical which prevent the growth of microorganisms.

Antibodies: Globular protein molecules (immunoglobulins) produced by plasma cells in response to stimulation by an antigen.

Antigen: Molecule that stimulates an immune response.

Antitoxin: Antibodies that render toxins harmless.

Antigen presenting cell: A cell that has ingested a pathogen and displays the pathogen’s antigens on its cell surface membrane.

B lymphocyte: Type of leucocyte that is produced and matures in the bone marrow.

Callose: Large polysaccharide deposited in phloem sieve tubes to block them.

Chemotaxis: The movement of cells or organisms towards or away from a particular chemical.

Clonal expansion: The multiplication of selected T and B lymphocytes in the specific immune response.

Clonal selection: The selection of T and B lymphocytes appropriate to an antigen in the specific immune response.

Cytokines: Cell signalling molecules which are used for communication between cells, allowing some cells to regulate the activity of others.

Endemic: A disease that is always present in a population.

Epidemic: The rapid spread of a disease through a high proportion of a population.

Herd immunity: A form of immunity that occurs when a significant portion of a population have been vaccinated and provides a measure of protection for individuals who have not developed immunity.

Histamine: Released by mast cells as part of the inflammatory response. Attracts neutrophils to the site of infection by chemotaxis and increases permeability of capillaries.

Immunoglobulins: Soluble glycoproteins molecules.

Immunological memory: Ability of the immune system to respond very quickly to antigens that it has encountered before due to the presence of memory cells.

Incidence rate: The number of new cases of a disease in a given population in a certain time period.

Inflammatory response: A tissue reaction to injury or an antigen that may include the release of histamine, pain, swelling, itching, redness, heat and loss of function.

Interleukins: A type of cytokine used to communicate between lymphocytes.

Lysozyme: An enzyme produced in tears which digests bacterial walls. keeping the eye free from infection.

Morbidity: The incidence or prevalence of a disease or of all disease in a population.

Mortality: The number of deaths in a population.

Opsonin: Molecule that binds to a pathogen, making it more susceptible to phagocytosis.

Pandemic: An epidemic that has spread worldwide.

Passive immunity: Immunity acquired by the transfer of antibodies.

Pathogen: An organism that causes disease.

Phagocytosis: Phagocytes engulf a pathogen in a vesicle called a phagosome. Lysosome fuse with the phagosome releasing digestive enzymes.

Plasma cells: Differentiated B lymphocytes that produce and secrete antibodies as part of the humoral response.

Ring vaccination: A vaccination of all susceptible individuals in a prescribed area around an outbreak of an infectious disease.

Specific immune response: An integrated immune response to an antigen, especially one mediated by lymphocytes.

T lymphocytes: Type of leucocyte that is produced in the bone marrow and matures in the thymus.

Toxins: A poisonous substance produced within living cells or organisms.

Transmission: Transfer of a pathogen from an infected individual to an uninfected individual.

T regulatory cells: T lymphocytes which suppress the function of other T cells to limit the immune response.

Vaccination: The administration of antigenic material (a vaccine) to stimulate an individual’s immune system to produce antibodies to a pathogen.

Vaccine: A safe form of an antigen, which is taken orally or injected into the bloodstream to provide artificial active immunity against a pathogen bearing the antigen.

Vector: An organism that transfers a pathogen from one host to another.