A mismatched double-stranded ribonucleic acid, which is an agonist for Toll-like receptor 3 (TLR3), is used in vitro or in vivo as an antimicrobial agent, antiproliferative agent, and/or immunostimulant. Poly(l:C11-14U) is a more selective agonist of TLR3 as compared to poly(l:C) even though the both double-stranded RNA are structurally analogous.