The TLR7 antagonist IRS661 partially reverses R837-mediated relaxation and completely reverses PolyUs- and PolyAs-mediated relaxation but does not reverse β2-adrenergic receptor–mediated relaxation of isolated guinea pig tracheas in vitro. Tracheal segments were preincubated with vehicle (open bars), IRS661 (solid bars), or propranolol (gray bars). Contraction of tracheal segments was induced by methacholine, and the effect of R837, PolyUs/As, or isoproterenol was measured (n = 3; maximum, 1.49 ± 0.10 g; R837 ± IRS661, P ≤ .01; PolyUs/As ± IRS661, P ≤ .001; isoproterenol ± propranolol, P ≤ .001). MCh, Methacholine.