Glossary terms

T2 lesion

Focal hyperintensity on T2-weighted MRI images. These lesions are non-specific, representing various brain parenchyma damage aetiologies. The appearance of new T2 lesions with temporospatial dissemination is part of the current the diagnostic criteria of multiple sclerosis (MS). Typical MS T2 lesions are small, oval or rounded, located around the ventricles, corpus callosum and/or subcortical white matter.

Demyelination

Damage to the myelin sheath surrounding nerves in the brain and spinal cord, which affects the function of the nerves involved. Demyelination occurs in multiple sclerosis, a chronic disease of the nervous system affecting young and middle-aged adults, and in experimental autoimmune encephalomyelitis, which is a mouse model of multiple sclerosis.

Experimental autoimmune encephalomyelitis

(EAE). An animal model of the human autoimmune disease multiple sclerosis. EAE is induced in experimental animals by immunization with myelin or peptides derived from myelin. The animals develop a paralytic disease with inflammation and demyelination in the brain and spinal cord.

Progressive multifocal leukoencephalopathy

A rapidly progressive, often fatal, human brain infection by the Jacob–Creutzfeldt (JC) virus, with tropism for oligodendrocytes. Common initial manifestations include cognitive, visual, motor and coordination dysfunction.

JC virus

A common human polyoma virus. Infection is usually subclinical in immunocompetent hosts, but it is associated with progressive multifocal leukoencephalopathy in immunocompromised individuals.

Tolerance

A term that denotes lymphocyte non-responsiveness to antigen, but implies an active process, not simply a passive lack of response.

CD4⁺CD25⁺ regulatory T (T_Reg) cell

A specialized type of CD4⁺ T cell that can suppress the responses of other T cells. These cells provide a crucial mechanism for the maintenance of peripheral self-tolerance and are characterized by expression of CD25 (also known as the -chain of the interleukin 2 receptor) and the transcription factor forkhead box P3 (FOXP3).

T cell

A T cell that expresses a T-cell receptor consisting of a -chain and a -chain. These T cells are present mainly in the intestinal epithelium as intraepithelial lymphocytes (IELs). Although the exact function of T cells (or IELs) is still unknown, it has been suggested that mucosal T cells are involved in innate immune responses by the mucosal immune system.

V2 T cells

This is a T-cell subset expressing the variable 2 chain in the surface T-cell receptor. The specific function of these cells remains unknown.

CD56^bright natural killer cell

This innate immune cell is characterized by lack of expression of CD3 and T-cell receptors and high expression of surface CD56 (also termed neural cell adhesion molecule; NCAM). This natural killer cell subset appears to have immunoregulatory function primarily, whereas CD56^dim natural killer cells function as potent cytolytic effectors.

Bystander suppression

The extension of tolerogen-induced suppression of immune responses that are directed against antigens not structurally related to the tolerogen but expressed by the same target cell or organ.

Anergy

A state of unresponsiveness to antigen. Anergic T cells or B cells cannot respond to their cognate antigens under optimal conditions of stimulation.

Altered peptide ligands

(APLs). APLs are peptide analogues that are derived from the original antigenic peptide. They commonly have amino-acid substitutions at T-cell receptor (TCR)-contact residues. TCR engagement by these APLs usually leads to partial or incomplete T-cell activation. Antagonistic APLs can specifically antagonize and inhibit T-cell activation that is induced by the wild-type antigenic peptide.

Plasmapheresis

The extracorporeal removal of blood plasma proteins from the circulation. Removal of circulating autoantibodies is used as therapy in several autoimmune disorders.

T_H3 cell

A regulatory T-cell subset that was originally described in oral tolerance, and that primarily secretes transforming growth factor- (TGF-). TGF- produced by T_H3 cells provides help for IgA class switching and has suppressive properties for both T_H1 and T_H2 cells. The expression of CD25 and forkhead box P3 (FOXP3) is induced in T cells under experimental T_H3-cell differentiation conditions.