Glossary

antigen processing

The process by which antigen is presented to lymphocytes in a form they can recognise. Most CD4+ T cells must be presented with antigen on MHC class II molecules, while CD8+ CTL cells only recognise antigen on MHC class I molecules. Antigen must be processed into peptide fragments before it can associate with MHC molecules

apoptosis

Type of cell death where particular cell populations die in a reproducible manner in every individual. Because of its predictable nature, this form of death was believed to occur as the result of a death ‘programme’, and so was named programmed cell death. Well-known examples are the loss of the cells between the digits (e.g. during the development of fingers). In adult tissues, cell death usually balances cell division, ensuring that tissues and organs retain the same size and structure as old cells are replaced. Apoptosis is a normal response in cells with DNA damage, serving to protect the body from cancer.

B cells

One of two main types of lymphocyte (cf. T cells) which, when activated, synthesises and releases huge quantities of soluble antibodies.

IgA

class of antibody that is prevalent in mucous secretions, and protects against infections in the gut, respiratory tree and genitourinary tract.

IgG

The main antibody in blood and tissue fluid. It has a large number of functions, including neutralising many toxic molecules, preventing viruses from attaching to cells, allowing phagocytes to recognise and internalise pathogens, and protecting the fetus and newborn babies. (It is the only antibody class that can cross the placenta.)

IgM

A class of antibody that is the first to be produced in an immune response.

immunoglobulins

An alternative name for soluble antibodies present in serum and tissue fluids.

immunological memory

the ability of the adaptive immune system to make an improved immune response on repeated encounters with the same antigen or pathogen.

lymphatic system

the connected system of lymphoid organs and lymphatic ducts present throughout the body.

lymphocytes

A major population of leukocytes including T cells, B cells and NK cells.

lymphoid organs

encapsulated organs such as thymus, lymph nodes and spleen and tonsils which contain collections of lymphocytes and cells involved in development of immune reactions.

lymphoid tissues 

include both the encapsulated organs of the immune system (eg lymph nodes) and unencapsulated collections of lymphocytes found in mucosal tissues.

MHC molecules

A group of proteins involved in antigen presentation to T cells.

NK cells

A group of lymphocytes that have the intrinsic ability to recognise and destroy some virally infected cells and some tumour cells.

proteasome

an intracellular organelle that breaks down proteins into polypeptide fragments.

T cells

Lymphocytes that differentiate primarily in the thymus and are central to the control and development of immune responses. The principle subgroups are cytotoxic T cells (Tc) and T helper cells (Th).