5.2 Antigens, pathogens and allergens

immune system

the body system that helps resist infection and disease through specialised cells and proteins

pathogens

agents that cause diseases in their hosts

antigens

molecules or parts of molecules that stimulate an immune response

antibodies

proteins produced by plasma cells in response to antigens and which react specifically with the antigen that induced their formation

self-antigens

antigens on cells that are recognised by self-receptors as being part of the same body

non-self antigens

antigens that do not belong to the bodys own cells

cell surface receptors

regions of a trans-membrane molecules exposed at the surface of a cell that act in cell signalling by receiving and binding to extracellular molecules

autoimmune disease

diseases in which the immune system fails to identify ‘self’ material and makes antibodies against the bodys own tissues

cell surface markers

proteins present on the plasma membrane that distinguish various cell types and discriminate between self and non-self antigens

cellular pathogens

any disease-causing agent made up of cells that can reproduce independently without relying on the host machinery

viruses

non-cellular pathogens that use the host cell in order to replicate their genetic material

prions

infectious particles made of protein that lack nucleic acids

non-enveloped viruses

viruses that lack an outer membrane

enveloped viruses

viruses with an outer envelope composed of part of the plasma membrane of the host cell when the viral particles bud from the cell

allergen

an antigen that elicits an allergic response

inflammation

an innate reaction by the immune response to foreign particles or injury resulting in redness and swelling

cytotoxic T cells

T cells that are activated by cytokines to bind to an antigen-MHC-I complexes on infected host cells and kill infected body cells

major histocompatibility complex (MHC)

receptor proteins on the surface of cells that identify the cells as ‘self’

MHC-I

a type of MHC found on nucleated cells

MHC-II

a type of MHC found on specific white blood cells involved in the adaptive immune response

antigen-presenting cells

cells of the immune system that use MHC-II markers on their surface to present antigens to helper T cells to elicit an immune response

macrophages

phagocytic antigen presenting cells derived from monocytes that may be found in various tissues throughout the body and can engulf foreign material

dendritic cells

a type of antigen-presenting cell and phagocyte that can activate T lymphocytes in the adaptive immune response

lysis

destruction of cells by rupturing the membrane of the cell