SECRETORY IGA INDUCES DEGRANULATION OF IL-3-PRIMED BASOPHILS

We examined whether secretory IgA (sIgA), known to mediate eosinophil stimulation, has an effect on basophil functions. An immobilized prepa ration of sIgA, but not of monomeric Igh, induced histamine release (a pproximately 15% of total histamine contents) from human basophils in vitro. sIgA-induced basophil histamine release was totally dependent o n pretreatment with IL-3, IL-5 and granulocyte-macrophage CSF also pri med basophils for sIgA-mediated release. Exogenous divalent ions, i.e. , Ca2+ and Mg2+, were essential for sIgA-mediated basophil degranulati on, and the degranulation was completed within 45 min. A newly synthes ized lipid mediator, leukotriene C-4, was also liberated front IL-3-pr imed, sIgA-stimulated basophils, Enzyme digestion experiments revealed that the (Fc)(2).secretory component portion of sIgA is important for sIgA-mediated basophil activation, but the functional binding sites o f sIgA on basophils were surmised to be different from Fc alpha R, The se observations reveal the novel finding that sIgA is able to stimulat e basophils as well as eosinophils. Since sIgA is the most abundant Ig isotype in the secretions from mucosal tissues, and basophils are act ive participants in allergic late-phase reactions, sIgA-mediated basop hil mediator release is potentially involved in exacerbation of the in flammation associated with allergic disorders.