"reagin" in the noun sense
an immunoglobulin E that is formed as an antibody against allergens (such as pollen attaches to cell membranes causing the release of histamine and other substances responsible for the local inflammation characteristic of an allergy
Source: WordNet® (An amazing lexical database of English)
Princeton University "About WordNet®."
WordNet®. Princeton University. 2010.
View WordNet® License