[mass noun](Immunology)the antibody which is involved in allergic reactions, causing the release of histamine when it combines with antigen in tissue, and capable of producing sensitivity to the antigen when introduced into the skin of a normal individual (免疫学)反应素;反应抗体 ■the substance in the blood which is responsible for a positive response to the Wassermann test 梅毒反应素
派生 reaginic adjective 语源
early 20th cent.: coined in German from reagieren 'react'