R112inhibitsdegranulationinducedbyanti-IgEcross-linkinginmastcells(tryptaserelease,effectiveconcentrationfor50%inhibition[EC50]=353nmol/L)orbasophils(histaminerelease,EC50=280nmol/L),andbyallergen(dustmite)inbasophils(histaminerelease,EC50=490nmol/L).R112alsoblocksleukotrieneC4productionandallproinflammatorycytokinestested.Itsonsetofactionisimmediate,andtheinhibitionisreversIBLe.R112isabletocompletelyinhibitallthreeIgE-inducedmastcellfunctions:degranulation,lipidmediatorproduction,andcytokineproduction.R112doesnotinhibitphosphorylationoftheLyntargetSyk(Y352),butinhibitsthephosphorylationoftheSyktargetLAT(Y191),indicatingthatSykkinaseistheprimarytargetofR112.MostphosphorylationeventsdownstreamofSykareinhibitedwithsimilarpotencybyR112.Invitrokinaseassaysdonotalwayscorrelatewiththecorrespondingactivityinsidecells.R112inhibitstheLynkinaseinvitroassaywithanIC50of0.3μmol/L;however,asmentionedpreviously,inCHMCs(Culturedhumanmastcells),R112doesnotinhibitthephosphorylationofSyk(Y352),andthereforemostlikelydoesnotinhibitLynactivity^[1].