T cell
A type of white blood cell known as a lymphocyte that expresses an antigen binding complex (T cell receptor – CD3 ) on the cell-surface. T cells bind processed antigen (antigenic peptides) presented by special cell surface (Major Histocompatibility Complex) molecules on antigen presenting cells or target cells.

T cell dependent/independent
T cell dependent antigens need immune recognition by both T- and B cells to produce an immune response. T cell independent antigens can directly stimulate B cells to produce specific antibody. However, T cell independent antigens are poorly immunogenic in infants and fail to induce immunological memory.

Titer
A measure of the strength of an antibody response e.g. the reciprocal of the last dilution of an antiserum capable of producing a specific effect (neutralizing antibody titer,etc.).

Toxin
A poisonous substance. Toxins may be of biological origin (biotoxins). Biotoxin may be produced by microorganisms, fungi and higher plants.

Vaccination
The use of a vaccine to induce specific immunity to prevent (prophylactic vaccination) or to treat (therapeutic vaccination) a disease.

Vaccine
A preparation of antigenic material or nucleic acid used to induce immunity against disease causing microorganisms (or their products) or cancer cells.

Vector
A DNA molecule, typically a plasmid or a viral replicon, used to propagate inserted DNA fragments (e.g. genes) in a host cell.

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