allergen desensitization An immunotherapeutic technique that aims either to change an allergic immune response to a symptom-free non-allergic response, or to develop immunologic tolerance to an allergen that has been causing unpleasant clinical symptoms. The procedure involves exposing an allergic individual to increasing doses of allergen.
allergic asthma An allergic reaction to inhaled antigen, which causes constriction of the bronchi, increased production of airway mucus, and difficulty in breathing.
allergic conjunctivitis An allergic reaction involving the conjunctiva of the eye that occurs in sensitized individuals exposed to airborne allergens. It is usually manifested together with nasal allergy symptoms as allergic rhinoconjunctivitis or hay fever.
allergic contact dermatitis A largely T-cell-mediated immunological hypersensitivity reaction manifested by a skin rash at the site of contact with the allergen. Often the stimulus is a chemical agent, for example urushiol oil from the leaves of the poison ivy plant, which can haptenate normal host molecules to render them allergenic.
allergic reaction A specific response to an innocuous environmental antigen, or allergen, that is caused by sensitized B or T cells. Allergic reactions can be caused by various mechanisms, but the most common is the binding of allergen to IgE bound to mast cells, which causes the cells to release histamine and other biologically active molecules that cause the signs and symptoms of asthma, hay fever, and other common allergic responses.
allergic rhinitis An allergic reaction in the nasal mucosa that causes excess mucus production, nasal itching, and sneezing.
allergy The state in which a symptomatic immune reaction is made to a normally innocuous environmental antigen. It involves the interaction between the antigen and antibody or primed T cells produced by earlier exposure to the same antigen.
alloantibodies Antibodies produced against antigens from a genetically nonidentical member of the same species.
alloantigens Antigens from another genetically nonidentical member of the same species.
allogeneic Describes two individuals or two mouse strains that differ at genes in the MHC. The term can also be used for allelic differences at other loci.
allograft A transplant of tissue from an allogeneic (genetically nonidentical) donor of the same species. Such grafts are invariably rejected unless the recipient is immunosuppressed.
allograft rejection The immunologically mediated rejection of grafted tissues or organs from a genetically nonidentical donor. It is due chieﬂy to recognition of nonself MHC molecules on the graft.
alloreactivity The recognition by T cells of MHC molecules other than self. Such responses are also called alloreactions or alloreactive responses.
altered peptide ligands (APLs) Peptides in which amino acid substitutions have been made in T-cell receptor contact positions that affect their binding to the receptor.
alternative pathway A form of complement activation that is initiated by spontaneous hydrolysis of C3 and which uses factor B and factor D to form the unique C3 convertase C3bBb.
alternatively activated macrophages See M2 macrophages.
alum Inorganic aluminum salts (for example aluminum phosphate and aluminum hydroxide); they act as adjuvants when mixed with antigens and are one of the few adjuvants permitted for use in humans.
amphipathic Describes molecules that have a positively charged (or hydrophilic) region separated from a hydrophobic region.
anakinra A recombinant IL-1 receptor antagonist (IL-1RA) used to block IL-1 receptor activation and used in treating rheumatoid arthritis.
anaphylactic shock See anaphylaxis.