Glossary

adaptive immune system

The adaptive immune defence refers to the tailoring of an immune response to the particular foreign invader. It involves differentiating self from non self and involves B cells and T cells (lymphocytes). A key feature of the adaptive immune system is memory. Repeat infections by the same virus are met immediately with a strong and specific response.

antigen

Originally defined as any molecule which the body recognised as ‘non-self’, and against which an antibody was produced. This definition was extended to include any molecule that the body could recognise as foreign. This includes the fragments of molecules that are recognised by T lymphocytes. In the broadest sense, it has always been known that the immune system can recognise self molecules, even if it does not usually react against them. Consequently, the widest definition of an antigen is a molecule that can be recognised by the immune system, of which there are conventional non-self antigens and self molecules or autoantigens.

anti-viral proteins

A group of proteins that are induced by interferon, which when activated, inhibit protein synthesis and viral replication.

chronic

One that continues to produce disease symptoms and tissue damage over many months or years; some chronic infections (e.g. malaria) are characterised by periods of remission and relapse but the pathogen is never completely eliminated from the body.

cytokines

short-lived, short-range signalling molecules primarily synthesised and secreted by leukocytes that affect the activity of other cells participating in an immune response.

glycoproteins

A protein with one or more covalently attached carbohydrate groups (usually short sugar chains). Addition of such groups to proteins, termed glycosylation, is a form of post-translational modification.

innate immune system

The elements of the immune system that are continuously active and that do not depend on immune recognition of antigens by lymphocytes. Innate immune responses do not improve with repeated encounters with the same antigen or pathogen.

interferons

Cytokines that interfere with viral replication by the induction of anti-viral proteins. There are 3 main types of interferon IFNα, IFNβ and IFNγ. IFNγ, produced by active T lymphocytes and NK cells has many additional effects in controlling immune responses and inflammation.

latent

One in which the pathogens persist in or on the host’s body, but without producing symptoms; during the latent period, the host may or may not be infectious (i.e. capable of transmitting the pathogens to others).

nucleocapsid

The core of a virus containing its genetic material (DNA or RNA), within a protein coat (capsid).

receptor-binding domain (RBD)

For Sars CoV2, this is the region of the spike protein that binds to the ACE2 receptor on a cell, as the first step in virus infection of the cell.

sterile immunity

The complete elimination by the host’s immune response of the pathogens responsible for an infectious disease (e.g. the influenza virus is eliminated from the body as the illness resolves).

toll-like receptors

A group of receptors, located on the plasma membrane or on intracellular vesicles, that recognise components of pathogens (PAMPs) and transduce signals for inflammation.

type-1 interferon (IFN)

A cytokine produced by many cell types that signals to other cells to inhibit replication of viruses.

viral envelope

A phospholipid membrane that surrounds the nucleocapsid of some groups of virus. It is derived from the plasma membrane of the virus-infected cell.

viral tropism

The tendency of a particular virus to target specific cells which it can infect and then replicate within.