Antigen: A substance that the immune system perceives as being foreign or dangerous. The body combats an antigen with the production of an antibody.
- Antigen-antibody complex
Antigen-antibody complex: The complex formed by the binding of an antibody to an antigen. Antigen-antibody complexes initiate immune responses. Also known as an immune complex.
- Antigen-presenting cell
Antigen-presenting cell: A cell that can “present” antigen in a form that T cells can recognize it. The cells that can “present” antigen include B cells and cells of the monocyte lineage (including macrophages).
- Antigenic drift
Antigenic drift: A mechanism for variation by viruses that involves the accumulation of mutations within the antibody-binding sites so that the resulting viruses cannot be inhibited well by antibodies against previous strains making it easier for them to spread throughout a partially immune population. Antigenic drift occurs in both influenza A and influenza B viruses.
- Antigenic shift
Antigenic shift: A sudden shift in the antigenicity of a virus resulting from the recombination of the genomes of two viral strains. Antigenic shift is seen only with influenza A viruses. It results usually from the replacement of the hemagglutinin (the viral attachment protein that also mediates the entry of the virus into the cell) […]
Drugs that combat the histamine released during an allergic reaction by blocking the action of the histamine on the tissue. Antihistamines do not stop the formation of histamine nor do they stop the conflict between the IgE and antigen. Therefore, antihistamines do not stop the allergic reaction but protect tissues from some of its effects. […]