Modifiers matching antigen:

• indoor,
• possible,
• exogenous,
• foreign,
• infectious,
• noninfectious,
• extraneous,
• outside,
• environmental,
• endogenous,
• harmless,
• single,
• microbial,
• strong,
• oral,
• nutritional,
• harmful,
• several,
• outdoor,
• small,
• simple,
• viral,
• particulate,
• soluble,
• diverse,
• internal,
• main,
• lethal,
• peripheral,
• extrinsic,
• perennial,
• dangerous,
• active,
• proteinaceous,
• bacterial,
• free,
• innocuous,

Simple categories matching perennial:

• pest,
• ornamental,
• allergen,
• plant,
• herb,
• vegetable,
• native,
• veggie,
• species,
• issue,
• grass,
• bunchgrass,
• wildflower,
• tree,
• river,
• seed,
• flower,
• planting,
• crop,
• antigen,
• weed,
• group,
• legume,
• shrub,
• fruit,
• clover,
• forage,
• pasture,
• host,
• vine,